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Mercury intrusion and permeability of Louiseville Clay
Abstract
Permeability and mercury-intrusion porosimetry tests were performed on a Champlain Sea clay for both intact and remoulded conditions after compression of the specimens to strains varying from 0 to 42%. The results show that for either intact or remoulded soil conditions, there is a relationship between the pore-size parameters and the permeability of the clay. However, there is no unique relationship for both intact and remoulded clays and for the silt and clay considered in previous studies. Consequently, mercury-intrusion porosimetry alone cannot be used to evaluate the permeability of soils in general. -from Authors
... If the PSD of a soft clay is bimodal, (a), compression progressively closes the inter-aggregate pores without significantly changing the total volume and the size of the intra-aggregate pores (b). From experience with Eastern Canada clays (Delage & Lefebvre, 1984;Lapierre et al., 1990;Locat, 1995), the aggregates forming the soft clays are at a water content close to the plastic limit of the soil. It is when the inter-aggregate pores are essentially closed (c) that the size and the total volume of the intraaggregate pores decrease (d). ...
... Probably one important aspect that could be added to the authors' soil fabric model is the effect of soil deposition in an environment with limited bioturbation that may give rise to surfaces of lower strength (bedding). Leblond (2002;see Leroueil et al., 2003) performed undrained torsional shear hollow cylinder tests on Louiseville clay, Quebec, at a depth close to that of the samples tested by Lapierre et al. (1990). The natural clay tested had a liquidity index of 1.1, a vertical yield stress ' vy of 180 kPa and was consolidated under an isotropic effective stress equal to 0.3 ' vy before shearing with the axis of the major principal stress axis at an angle to the vertical that varied from 0° (conventional compression) to 75°. ...
... A partial explanation may come from the observation (at least for Eastern Canada clays; e.g. Lapierre et al., 1990) that the observed roughness along horizontal planes is smaller than along vertical planes. More generally, it may come from the slow deposition process and the smoothing of the sea bottom by water currents and animals. ...
... There are several parameters that can affect the soil-water retention curve, such as soil structure, soil type, initial water content, void ratio, mineralogy, the distribution of pore sizes and densities, the density of organic material, the clay content, and the contact angle (e.g., [65][66][67]). For a uniform soil with a narrow range of pore sizes, the SWRC curve consists of three different sections: a straight segment up to the air entry pressure, a nearhorizontal behavior within the middle part, and a relatively vertical end section. ...
... There are several parameters that can affect the soil-water retention curve, such as soil structure, soil type, initial water content, void ratio, mineralogy, the distribution of pore sizes and densities, the density of organic material, the clay content, and the contact angle (e.g., [65][66][67]). For a uniform soil with a narrow range of pore sizes, the SWRC curve consists of three different sections: a straight segment up to the air entry pressure, a near-horizontal behavior within the middle part, and a relatively vertical end section. ...
... Soil compressibility and pore size distribution in response to suction influence the shape of SWRC. The mineralogy, soil structure, initial water content, and stress history have an impact on these two porous material features (e.g., [65][66][67]). Soil pore size distribution has an effect on the shape of SWRCs, which tend to form in a S shape. ...
The soil water retention curve (SWRC) or soil–water characteristic curve (SWCC) is a fundamental feature of unsaturated soil that simply shows the relationship between soil suction and water content (in terms of the degree of saturation and volumetric or gravimetric water content). In this study, the applications of the SWRC or SWCC have been extensively reviewed, taking about 500 previously published research studies into consideration. This was achieved on the basis of classification-based problems and application-based problems, which solve the widest array of geotechnical engineering problems relevant to and correlating with SWRC geostructural behavior. At the end of the exercises, the SWRC geostructural problem-solving scope, as covered in the theoretical framework, showed that soil type, soil parameter, measuring test, predictive technique, slope stability, bearing capacity, settlement, and seepage-based problems have been efficiently solved by proffering constitutive and artificial intelligence solutions to earthwork infrastructure; and identified matric suction as the most influential parameter. Finally, a summary of these research findings and key challenges and opportunities for future tentative research topics is proposed.
... It has been well documented that the hydraulic conductivity can be influenced by many factors, including the chemical properties of fluid, void ratio, mineralogy, grain size and shape, grain packing and orientation, pore size distribution and pore interconnection (Yin et al., 2009;Ren et al., 2016;Teng et al., 2019). Several investigators attempted to develop some empirical and theoretical models to predict the hydraulic conductivity from easily determinable physical characteristics of soils (Lapierre et al., 1990;Dolinar, 2009). In most empirical models, the hydraulic conductivity was related to the selected properties of soils, such as void ratio (Berilgen et al., 2006;Dolinar, 2009), effective grain size (Chapuis, 2004) and representative pore size (Deng et al., 2015). ...
... The parameter Np refers to the pore interconnection and reflects the pore tortuosity. To further analyse the influence of Np, Eq. (10) with Np=1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 was applied to compute the PSP of MX80 bentonite/COx claystone mixtures, Louiseville clay (Lapierre et al., 1990), Shanghai muddy clay (Tang and Yan, 2015), and Rajasthan monovalent bentonite (Jadda and Bag, 2020) using the respective pore size distributions. As an example, the details of calculating the PSP value with Np= 4 for the compacted MX80 bentonite/claystone mixture with a bentonite fraction of 30% and void ratio of 0.62 are described in Appendix A. In Fig. 8, the measured hydraulic conductivity is presented versus the PSP value for Np=1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, together with estimated hydraulic conductivity using Eq. ...
... Based on the Poiseuille's equation for laminar flow through a capillary tube, the hydraulic conductivity for a distribution of capillary tubes (kc) having different diameters di can be expressed as (Lapierre et al., 1990): (12) where n is the porosity; μ is the water viscosity; i is the counter from 1 to l; di and f(di) are the pore diameter and volumetric probability corresponding to i, respectively. According to Eq. (12), the following equation can be deduced to describe the ratio of the liquid-water hydraulic conductivity in unsaturated state to the saturated one (kr) (Burdine, 1953;: ...
In the French concept of deep geological disposal, the underground repository is planned to be constructed in Callovo-Oxfordian (COx) claystone formation. To reduce the excavation wastes, a mixture of MX80 bentonite and excavated COx claystone in compacted blocks has been proposed as a candidate sealing/backfill material by the French National Agency for Nuclear Waste Management (ANDRA). When the repository is closed, the compacted blocks are expected to swell, filling up the technological voids, resisting the propagation of excavation-damaged zone and preventing the release of radionuclides into the biosphere. To assess the suitability of the proposed material, a laboratory programme was set up in this PhD study to characterize the hydro-mechanical behaviour of compacted bentonite/claystone mixture under different environmental conditions.Compression, swelling pressure, hydraulic conductivity and mercury intrusion porosimetry (MIP) tests were performed on the compacted MX80 bentonite/COx claystone mixtures with various bentonite fractions, dry densities and water contents for the preliminary performance assessment of the material. By considering the interaction between bentonite and claystone during hydration, the claystone void ratio and volumetric fraction in the mixture were deduced and the swelling pressure of claystone grains was indirectly determined. Moreover, two analytical methods were proposed to predict the swelling pressure and hydraulic conductivity of bentonite/claystone mixtures. Additionally, based on the pore size distribution after hydration, the swelling pressure and hydraulic conductivity of bentonite/claystone mixtures were further evaluated.Afterwards, the aeolotropic swelling behaviour of compacted MX80 bentonite/COx claystone mixture with axial/radial technological voids was experimentally determined. Results show that axial technological voids could decrease the grain orientation and reduce the aeolotropy. By contrast, radial technological voids would increase the heterogeneity and enhance the aeolotropy.In addition, the homogenization process of compacted blocks with technological voids was experimentally and theoretically evaluated. The evolutions of axial and radial swelling pressures and hydraulic conductivity over time were investigated, together with the determination of the variations of water content, dry density, suction and microstructure distribution. Particular attention was paid to the effect of boundary friction between the samples and porous stones and an analytical method was proposed to estimate the final dry density distribution of samples with technological voids.To account for the influences of the pore water in COx claystone and the cementitious solution due to concrete degradation, compacted bentonite/claystone mixtures with various bentonite natures, dry densities and technological voids were hydrated with deionised water, synthetic site water and cementitious solution and the swelling pressure, hydraulic conductivity and microstructure were determined. Results show that the synthetic site water and cementitious solution slightly decreased the swelling pressure and increased the hydraulic conductivity due to the cation exchange and montmorillonite dissolution.Finally, water flow in the unsaturated MX80 bentonite/COx claystone mixture was investigated by carrying out infiltration and water retention tests under constant-volume conditions alongside microstructure observation. The hydraulic conductivity was experimentally determined. Based on the evolving pore structure upon hydration, two-phase hydraulic conductivities were predicted and a numerical model was developed to investigate the contribution of vapour and liquid water flux
... From literature review, 329 saturated hydraulic conductivity values, determined by laboratory tests [17,21,[24][25][26][27][28][29], were collected. The main geotechnical characteristics of the soils studied by different authors are shown in Table 2. Table 2. Main geotechnical characteristics of tested soils [17,21,[24][25][26][27][28][29]. ...
... From literature review, 329 saturated hydraulic conductivity values, determined by laboratory tests [17,21,[24][25][26][27][28][29], were collected. The main geotechnical characteristics of the soils studied by different authors are shown in Table 2. Table 2. Main geotechnical characteristics of tested soils [17,21,[24][25][26][27][28][29]. ...
... The clay tested by [24] was a grey marine plastic Champlain Sea clay from Louiseville (Quebec). IP is 38%, w L is 68%, and C F (percentage of particles smaller than 2 µm) is 80%. ...
Predictive models able to provide a reliable estimate of hydraulic conductivity can be useful in various geotechnical applications. Since most of the existing predictive methods for saturated hydraulic conductivity estimation are valid only for a limited range of soils or can be applied under certain restrictive conditions, a new method applicable to clayey soils and clayey or silty sands having a wide range of values of soil index properties is proposed in this study. For this purpose, 329 saturated hydraulic conductivity values, obtained by laboratory tests carried out on different soils, were collected in a database and used to develop five equations using a multiple regression approach. Each equation correlates the hydraulic conductivity with one or more geotechnical parameters. An equation was developed that predicts, within an order of magnitude, the saturated hydraulic conductivity in the range from 1.2 × 10 −11 to 3.9 × 10 −6 m/s, based on simple geotechnical parameters (i.e., clay content, void ratio, plastic limit, and silt content).
... Microscopic experiments based on these high-tech approaches revealed that the microfabric and the micropore structure essentially control the permeability of soils (Li et al., 2013;Yuan et al., 2018;Gao et al., 2019). This result prompted many researchers to focus on the correlation between soil permeability and various microstructural parameters (Garcia-Bengochea et al., 1979;Juang and Holtz, 1986;Lapierre et al., 1990;Schaap and Lebron, 2001;Gao and Hu, 2013;Ranaivomanana et al., 2016). Among these, the relation between permeability and the pore size distribution (PSD) has become an issue of great concern. ...
... Garcia- Bengochea et al. (1979) defined a pore size parameter (PSP) based on the MIP results and proposed a power law between the PSP and the permeability of fine-grained soils. However, as Lapierre et al. (1990) commented, the model of Garcia-Bengochea et al. (1979) usually overestimates the permeability of clay and cannot give a unique function. Juang and Holtz (1986) developed a probability-based model to link the permeability of soil with the pore size density function. ...
... This means that the microporosity yielded by MIP can be regarded as the effective porosity for fluid flow. Despite these limitations, many researchers have successfully characterized the PSD of clayey soils using this technique (Lapierre et al., 1990;Delage et al., 2010). The results of the MIP tests are usually represented by the cumulative and differential curves of intruded volume per unit mass of the sample. ...
This work aimed to propose a semi-empirical model that predicts the permeability of saturated clay using the data of mercury intrusion porosimetry (MIP). First, the pore size distribution (PSD) curve obtained from an MIP test was regarded as a discrete probability function of pore diameters; thus, its shape could be characterized by probability parameters (e.g., the expected value and the standard deviation). Subsequently, these probability parameters, combined with the microporosity calculated from the volume of intruded mercury, were correlated with the permeability of clay based on Hagen-Poiseuille's equation. Next, the performance of the proposed permeability model was verified using data reported in the literature. Thereafter, the model was applied to estimate the permeability of normally consolidated (NC) and overconsolidated (OC) kaolin subjected to various triaxial loading. The results highlighted that the proposed model is capable of characterizing the sensitive variation of kaolin permeability under different overconsolidation ratios (OCRs), stress paths, and stress levels.
... In the late seventies, pioneer SEM applications to the investigation of the effects of loading on clay microstructure, i.e., post-mortem investigations (Tovey, 1973;Sfondrini, 1975;Tavenas et al., 1979;Sides & Barden, 1971;Mitchell, 1976;Smart & Tovey, 1981;Cotecchia et al., 1982;Delage & Lefebvre, 1984), already provided evidence of the microstructural changes in the background of given clay stress-strain responses. Since then, SEM, later combined with Mercury Intrusion Porosimetry, MIP (Diamond, 1970;Romero & Simms, 2008), have been used in experimental studies of the dependence of clay macro-behaviour on clay microstructure (e.g., Delage & Lefebvre, 1984;Griffiths & Joshi, 1990;Locat, 1995;Lapierre et al., 1990;Cotecchia & Chandler, 1997, 1998Delage, 2010;Hattab & Fleureau, 2010;Hicher et al., 2000;Cetin, 2004;Monroy et al., 2010;Hattab et al., 2013;Cotecchia et al., 2016Cotecchia et al., , 2019Mitaritonna et al., 2014;Guglielmi et al., 2018Guglielmi et al., , 2023Guglielmi et al., , 2024Jia et al., 2020). Nonetheless, the exploration of micro-mechanical modelling of clays has become a main research issue only in the last decade, prompted by the parallel intense development of micro-mechanical modeling of coarse soil behaviour. ...
... The DPS tends to correspond to the porosity present within the stacks, as recognized by Guglielmi et al. (2024) through the micrograph inspections. Hence, these results enhance the previous knowledge about the changes in PSD of clays under 1D compression (Delage & Lefebvre, 1984;Lapierre et al., 1990;Tanaka & Locat, 1999;Hattab & Fleureau, 2010;Hattab et al., 2013), indicating that both the inter-aggregate and the intra-aggregate porosity change with compression. ...
This keynote lecture discusses the results of a long lasting experimental research, devoted to the investigation of clay microstructure and its evolution upon loading. Micro-scale analyses, involving scanning electron microscopy, image processing, mercury intrusion porosimetry and swelling paths to test the clay bonding, are presented on clays subjected to different loading paths, with the purpose of providing experimental evidence of the processes at the micro-scale which underlie the clay response at the macro-scale. Data from the literature on clays of different classes, either soft or stiff, are compared to original results on two stiff clays, Pappadai and Lucera clay, both in their natural state and after reconstitution in the laboratory. The results presented herein allow building a conceptual model of the evolution of clay microstructure upon different loading paths, providing microstructural insights into the macro-behaviour described by constitutive laws and advising their mathematical formalization in the framework of either continuum mechanics or micro-mechanics. For editorial purposes, the research results are presented in two parts. The first part, presented in this paper, concerns the results for reconstituted clays, whereas a second part, concerning the corresponding natural clays, is discussed in a second companion paper.
... In situ tests performed at each sites (see Figure 3 for location of these sites). X-ray diffraction of powder samples of the bulk specimen and of oriented samples of the clay fraction (CF), scanning electron microscope (SEM) observations and mercury intrusion porosity [17,18] were carried out on some samples to obtain information on the mineralogy and the micro-fabric of the soil. Specific surface area and cationic exchange capacity were also measured as well as organic matter, calcite content, and pore water salinity estimated from electric resistivity. ...
... Due to a greater burial depth than the sample shown in Figures 10a-c, this sample presents a more compact fabric which makes it more difficult to evaluate the clay-flake orientation. On the other hand, the compaction from burial depth reached a point where most of the inter-aggregate pores are closed, while the intra-aggregate pores size has likely remained similar since their formation [17,18,24]. It is also interesting to note that at a magnification of 5000, large aggregates of particles (up to 10 μm in diameter) are visible just below the large diatom skeleton (at coordinate [6,16] in Figure 10f). ...
On May 10th 2010, a landslide occurred along the Salvail River in the municipality of Saint-Jude, tragically killing the four members of a family. The Ministère des Transports du Québec in collaboration with Université Laval carried out a detailed investigation to characterize the soil involved in this landslide. The investigation included field observations, in situ testing, sampling using thin-wall tubes, as well as laboratory tests that enabled to obtain information on the stratigraphy of the deposit and the geotechnical, mineralogical, micro-fabric and physico-chemical properties of the soils involved in the landslide. The stratigraphy and geotechnical properties were found to be uniform around the landslide. The clayey deposit is composed of various minerals dominated by quartz and feldspar, with a clay fraction containing large amounts of illite (or mica-like minerals) and a flocculated fabric. The soil involved in the landslide consists mainly of sensitive grey clay, typical of Canadian Champlain Sea clays, with a liquidity index varying between 2 and 1 from top to bottom of the deposit, intact shear strength increasing linearly with depth from 25 to 65 kPa, and an OCR decreasing with depth from 1.9 to 1.2. High quality samples were also taken using the Laval sampler. Triaxial tests were performed on these samples to characterized the mechanical behaviour of the Saint-Jude clay and its critical and limit states. The critical state is defined by a friction angle in the normally consolidation range of 30.6° and a cohesion of 5 kPa. The limit state is centered around the normally consolidated coefficient of earth pressure at rest line, with a peak strength envelope beyond the critical state envelope and an isotropic limit state equal to 0.7σ’p,typical for Champlain Sea deposits.
... Surface topography and micro fractures related to the de-stressing and drying of geological samples were excluded (see Table 1). The Washburn equation [41,42] is derived for cylindrical pores and calculations were carried out assuming a contact angle 141° between mercury and the particle surface, and a surface tension of 0.485 N m −1 [24,43,44]. The mercury pressures were used to predict pore throats (constrictions) with equivalent diameters between 1093 nm at 1.379 MPa and 5.6 nm at 268.9 MPa. ...
... The pore throats are obvious restrictions in the pore structure and are typically a fraction of the pore size. The Washburn equation [42] was used to calculate the equivalent pore diameters for mercury entering pores at specific pressures [24,41,43,44]. At a pressure of 1.379 MPa mercury enters pores of > 1093 nm diameter and this allows the shale bulk density (ρ HgBulk ) to be determined. ...
... It has been well documented that the hydraulic conductivity can be influenced by many factors, including the chemical properties of fluid, void ratio, mineralogy, grain size and shape, grain packing and orientation, pore size distribution and pore interconnection (Yin, 2009;Ren et al., 2016;Teng et al., 2019). Several investigators attempted to develop some empirical and theoretical models to predict the hydraulic conductivity from easily determinable physical characteristics of soils (Lapierre et al., 1990;Dolinar, 2009). In most empirical models, the hydraulic conductivity was related to the selected properties of soils, such as void ratio (Berilgen et al., 2006;Dolinar, 2009), effective grain size (Chapuis, 2004) and representative pore size (Deng et al., 2015). ...
... To further analyse the influence of N p , Eq. (10) with N p = 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 was applied to compute the PSP of Z. Zeng, et al. Engineering Geology 278 (2020) 105826 MX80 bentonite/COx claystone mixtures, Louiseville clay (Lapierre et al., 1990), Shanghai muddy clay (Tang and Yan, 2015), Al-Ghat soil (Elkady et al., 2016), Wuhan clay , Nanyang clay , Maryland clay (Yuan et al., 2019) and Rajasthan monovalent bentonite (Jadda and Bag, 2020) using the respective pore size distributions. As an example, the details of calculating the PSP value with N p = 4 for the compacted MX80 bentonite/claystone mixture with a bentonite fraction of 30% and void ratio of 0.62 are described in Appendix A. In Fig. 8, the measured hydraulic conductivity is presented versus the PSP value for N p = 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10, together with estimated hydraulic conductivity using Eq. ...
Soil hydraulic conductivity depends not only on the state variables such as void ratio and pore size distribution, but also on its physical/geotechnical properties. In this study, Atterberg limits, hydraulic conductivity and mercury intrusion porosimetry (MIP) tests were performed on MX80 bentonite/Callovo-Oxfordian (COx) claystone mixtures. Based on the experimental results obtained in this study together with the test data compiled from literature, a general capillary model considering Np pores in series was used to evaluate the influence of soil plasticity on the relationship between hydraulic conductivity and pore size distribution. It was found that the best pore interconnection parameter Np was highly dependent on the soil property. The larger the plasticity index, the larger the best Np value and the more complex the pore interconnection. The relationship between the best Np value and plasticity index could be well described by an exponential equation. The general capillary model was then improved to estimate the hydraulic conductivity of different soils. The estimated values using the improved general capillary model were finally compared with the measured ones and the good agreement between the measurement and estimation revealed the good performance of the proposed model.
... Surface topography and micro fractures related to the de-stressing and drying of geological samples were excluded (see Table 1). The Washburn equation [41,42] is derived for cylindrical pores and calculations were carried out assuming a contact angle 141° between mercury and the particle surface, and a surface tension of 0.485 N m −1 [24,43,44]. The mercury pressures were used to predict pore throats (constrictions) with equivalent diameters between 1093 nm at 1.379 MPa and 5.6 nm at 268.9 MPa. ...
... The pore throats are obvious restrictions in the pore structure and are typically a fraction of the pore size. The Washburn equation [42] was used to calculate the equivalent pore diameters for mercury entering pores at specific pressures [24,41,43,44]. At a pressure of 1.379 MPa mercury enters pores of > 1093 nm diameter and this allows the shale bulk density (ρ HgBulk ) to be determined. ...
Abstract Shale gas is an important hydrocarbon resource in a global context. It has had a significant impact on energy resources in the US, but the worldwide development of this methane resource requires further research to increase the understanding of the relationship of shale structural characteristics to methane storage capacity. In this study a range of gas adsorption, microscopic, mercury injection capillary pressure porosimetry and pycnometry techniques were used to characterize the full range of porosity in a series of shales of different thermal maturity. Supercritical methane adsorption methods for shale under conditions which simulate geological conditions (up to 473 K and 15 MPa) were developed. These methods were used to measure the methane adsorption isotherms of Posidonia shales where the kerogen maturity ranged from immature, through oil window, to gas window. Subcritical methane and carbon dioxide adsorption studies were used for determining pore structure characteristics of the shales. Mercury injection capillary pressure porosimetry was used to characterize the meso and macro porosity of shales. The sum of the CO2 sorption pore volume at 195 K and mercury injection capillary pressure pore volumes (1093–5.6 nm) were equal to the corresponding total pore volume (
... Mitchell and Kuhn [15] used DEM to simulate creep in granular material. The inter-particle forces in clay include the mechanical forces, attractive (Van der Waals) force and diffuse double layer (DDL) repulsive force [5,19,23] Porosimetry of both natural and resedimented clay has indicated that water may be present in the micro-or macro-pores of a soil skeleton [24][25][26]. The water present in the micro-pores will have reduced mobility because of the physicochemical interactions between the clay crystals and the pores [17], as the surfaces of clay minerals allow them to adsorb water [16]. ...
... Different pore structures and particle gradations have a great influence on the k v [20][21][22]. Clement [23] investigated the relationship between the type of pore distribution and the k v under different consolidation stresses by means of mercury injection testing. The study of Kong Lingwei [24] also found that the k v does not change much when the content of fine particles in the sandy soil is less than 5%. ...
The study of deep soil mechanics is the basis of deep shaft construction. Exploring the nonlinear permeability mechanism of deep confined aquifers in depth is the prerequisite and foundation for carrying out calculations of the hydrophobic consolidation settlement of thick alluviums and preventing and controlling deep-well-damage disasters. Against the background of shaft damage caused by hydrophobic consolidation settlement of the bottom aquifer of thick alluviums, a joint HPLTC-HPPNP (high-pressure long-term consolidation and high-pore-pressure nonlinear permeability) test was carried out on the bottom aquifer of thick alluviums based on the ETAS test system. This paper studied the evolution law of the permeability coefficient (kv) of bottom aquifers under different heads of confined water, confining pressures (σr), permeability hydraulic gradients (i) and loading–unloading methods. The internal pore structure characteristics of clayey sand were obtained by using low-field nuclear magnetic resonance (NMR) technology to explore the clayey sand’s nonlinear permeability micro-mechanism. The research results showed that the bottom aquifer seepage volume (ΔQi) under high stress is affected by the head pressure difference and pore water dissipation, and kv decreases with an increasing σr according to the power function relationship. The influence of the hydraulic gradient (i) on kv is significantly influenced by σr. When σr < 4 MPa, kv decreased with an increasing i, and when σr > 4 MPa, kv increased with an increasing i first, then decreased, before then tending to be stable. Under different stress states, the T2 spectrum of clayey sand showed a bispectrum peak type, and the adsorbed water content decreased linearly with an increasing σr, while the capillary water decreased according to the power function. The content of capillary water in the permeable pores plays a key role in the permeability of clayey sand, and it has a power function relationship with σr. The research results of this paper provide a good experimental method for the study of deep soil permeability characteristics and parameter determination, provide a theoretical basis for deep alluvial hydrophobic consolidation and settlement, and further make up for the shortcomings of existing deep soil mechanics in permeability characteristics.
... The marine soft clay generally presents flocculated structure due to the salt-water environment [16,33,34]. The pore size below 0.4 μm belongs to the introaggregate pore, while the pore size over 0.4 μm belongs to the interaggregate pore [33,35]. Higher proportion of large interaggregate pores (d > 10 μm) in layer ③ was likely resulted from the higher silt content (over 70%), which could form a granular-link bound structure and large interparticle pores [34]; layer ④ exhibited higher content of interaggregate pores than layer ⑤, indicating a more flocculated structure than layer ⑤. ...
Aquifers in China’s southeast coastal areas are protected by the overlying marine soft clays formed in Holocene transgression. However, a fundamental understanding of the characteristics of DNAPL (dense nonaqueous phase liquid) contamination in marine soft clays is limited. The study was conducted on the site of a former pharmaceutical factory in Shanghai, where serious 1,1,2-trichloroethane (DNAPL) contamination was detected up to the depth of 22.0 m below the existing grade. Partitioning calculation method was used to identify the presence of pure phase, and the results showed that pure 1,1,2-trichloroethane was accumulated at the interface of the upper soft silty clay and lower soft clay. The vertical transport was believed to be the pure DNAPL displacing pore water following the principle of two-phase flow, rather than the convection and diffusion of aqueous phase. The contamination (NAPL-soil interaction) impacted the soil properties slightly, and this effect could not account for the deep contamination. Soil structure analysis showed that these clays contained a proportion of large interaggregate pores, providing pathways for the transport of pure DNAPL. Considering their flocculated structure, the marine soft clays are not capable to perform as a barrier to prevent the downward migration of pure DNAPL.
... Therefore, the water retention curve depends on pore size distribution, and this is the origin of the definition of the water retention curve, firstly defined as a tool to estimate soil permeability [16,17]. Naturally that the changes of water-retention properties were then investigated as a function of the evolution of pore size distribution caused by grading size distribution, as well as stress and suction changes [18][19][20]. Further studies allowed us to better understand the coupled hydro-mechanical behavior of the soils occurring during wetting and drying, particularly when volume changes caused by water absorption and desorption were relevant (clayey soils), and how this behavior was affecting the measurement of the water retention curves (for example, see References [15,[21][22][23][24]). ...
Biocementation is a soil treatment technique wherein bacteria living in soil pores promote the precipitation of calcium carbonate. One of the most recent applications of this treatment is to provide resistance against the erosion of slopes by creating a resistant cover but still allowing infiltration to avoid water runoff. For modeling infiltration, it is fundamental to know the water retention curve of the treated material. This may not be an easy task because the soils most suitable for biocementation treatment are sands, due to their large pore sizes and consequent high permeability. The water retention curves (WRCs) of such types of soil are characterized for having a very small air entry value, followed by an almost-horizontal zone, which cannot be measured by using the vapor equilibrium, most of the existing sensors, or a water dewpoint potentiometer. Data from mercury intrusion porosimetry (MIP) tests can be used as an alternative to find the WRC, and this is explored in this paper. The model for the water retention curve presented considers the deformability of the soil during the MIP test, assuming an isotropic elastic behavior. The WRC derived from the MIP tests is well-fitted to the points measured by using a water dewpoint psychrometer (only for suctions above 1 MPa) and vapor equilibrium.
... Delage and Lefebvre 18 studied the pore changes during the consolidation of Champlain clay samples using MIP and SEM, and explained the correlation between soil particle adjustment and changes in pore characteristics based on analysis of the pore change rule during clay deformation. Lapierre et al. 19 developed a mathematical formula relating the pore distribution characteristic parameters and the permeability coefficient of undisturbed soil and remolded soil under different consolidation stresses based on mercury injection tests. They stated that there were no unified mathematical models for the pore characteristic parameters and permeability coefficient of undisturbed soil and remolded soil. ...
This paper investigates the regularity of microstructural evolution of Shenzhen granite residual soil in an attempt to determine its macrostructural deformation characteristics. The pore distribution and microstructure characteristics of granite residual soil are examined experimentally under different consolidation stresses, coupled with mercury injection tests and scanning electron microscopy. It is found that a microstructure exists in the granite residual soil and that the structural characteristics of granite residual soil in Shenzhen. The calculated pre-consolidation stress and structural yield strength of the granite residual soil are similar, indicating a phenomenon that resembles over-consolidation in the granite residual soil. This is fundamentally different from the mechanism of conventional over-consolidation in soil. It is also found that the relationship between the increment of mercury in soil samples and the stress of the mercury under different consolidation stresses is mainly trimodal. The significance of the research presented in this paper lies in the development of a clear understanding of the influence of the microstructure characteristics of granite residual soil on its macrostructural deformation, thereby providing a theoretical basis for engineering applications involving granite residual soil and the analysis of foundation deformation.
... Soil microstructure strongly contributes to the mechanical and hydraulic properties of soils such as permeability (Garcia-Bengochea et al., 1979;Lapierre et al., 1990;Yuan et al., 2019b), compressibility (Delage, 2010;Delage and Lefebvre, 1984), water retention (Romero et al., 2011;Seiphoori et al., 2014;Yuan et al., 2019b) and strength (Liu et al., 2016a;Ng et al., 2020). As pointed out by, among others, Yuan et al. (2019aYuan et al. ( , 2019bYuan et al. ( , 2021a, wetting collapse behaviour, permeability and swelling behaviour are strongly affected by the macropores of soil. ...
Soil properties, such as wetting collapse behaviour and permeability, are strongly correlated to the soil microstructure. To date, several techniques including mercury intrusion porosimetry (MIP), can be used to characterize the microstructure of soil, but all techniques have their own limitations. In this study, the features of mercury that penetrated and has been entrapped in the pore network of the specimens through MIP testing were investigated by X-Ray microtomography (X-μCT), in order to give an insight into the geometry of macropores and possible ink-bottle geometry. Two conditions of water content and density were selected for the compacted Maryland clay. The distribution and geometry features of mercury entrapped in the microstructure after MIP were characterized and pore size distributions were also reconstructed. The results suggest that, for the two conditions studied in this paper, macropores were evenly distributed within the specimens, and most of them with a non-spherical shape, and with aspect ratio (ratio between the maximum and minimum thickness along a given segment) smaller than three. Different dominant entrance pore size of macropore was obtained from MIP and X-μCT, due to the specific experimental protocol used in tests and the effect of ink-bottle geometry. Only the large pore bodies with high aspect ratio were imaged in X-μCT, due to the extrusion of mercury during the process of depressurization and subsequent sample preparation for X- μCT. But entire pore space was accessible in MIP. The difference in dominant entrance pore size was more significant for specimens with lower void ratio due to a more pronounced aspect ratio.
... Subsequently, some researchers (eg. Collins and McGown, 1974;Ahmed et al., 1974;Pusch, 1982;Delage and Lefebvre, 1984;Alonso et al., 1987;Lapierre et al., 1990) imbibed this concept and have interpreted PSD curves with two distinctly different peaks, in most cases, for compacted soils. Gens and Alonso (1992) believed that the two peaks represent micro-and macro-voids, respectively. ...
Variability in moisture content is a common condition in natural soils. It influences soil properties significantly. A comprehensive understanding of the evolution of soil microstructure in wetting/drying process is of great significance for interpretation of soil macro hydro-mechanical behavior. In this review paper, methods that are commonly used to study soil microstructure are summarized. Among them are scanning electron microscope (SEM), environmental SEM (ESEM), mercury intrusion porosimetry (MIP) and computed tomography (CT) technology. Moreover, progress in research on the soil microstructure evolution during drying, wetting and wetting/drying cycles is summarized based on reviews of a large body of research papers published in the past several decades. Soils compacted on the wet side of optimum water content generally have a matrix-type structure with a monomodal pore size distribution (PSD), whereas soils compacted on the dry side of optimum water content display an aggregate structure that exhibits bimodal PSD. During drying, decrease in soil volume is mainly caused by the shrinkage of inter-aggregate pores. During wetting, both the intra- and inter-aggregate pores increase gradually in number and sizes. Changes in the characteristics of the soil pore structure significantly depend on stress state as the soil is subjected to wetting. During wetting/drying cycles, soil structural change is not completely reversible, and the generated cumulative swelling/shrinkage deformation mainly derives from macro-pores. Furthermore, based on this analysis and identified research needs, some important areas of research focus are proposed for future work. These areas include innovative methods of sample preparation, new observation techniques, fast quantitative analysis of soil structure, integration of microstructural parameters into macro-mechanical models, and soil microstructure evolution characteristics under multi-field coupled conditions.
... Delage and Lefebvre (1984) employed Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) to study the effect of consolidation on intact, remoulded and reconstituted Canadian sensitive clays. Since the seminal work of Delage and Lefebvre (1984), Electron Microscopy and MIP have greatly contributed to revealing the evolving microstructure of artificial and natural clays before and after mechanical perturbation (Lapierre et al., 1990;Tanaka and Locat, 1999;Mitaritonna et al., 2014;Cotecchia et al., 2019). Hattab and her co-workers (Hattab and Fleureau, 2010;Hattab et al., 2013) studied the evolution of the fabric orientation in relation to stress history for, respectively, reconstituted kaolin and reconstituted natural clays. ...
Unique 4D deformation data are collected during drained triaxial tests on intact specimens of a natural sensitive clay. This required the development of a miniature triaxial cell for advanced stress path testing, specifically designed for X-ray Computed Tomography (XCT). Salient features include the omission of membrane, and a mounting procedure that minimises disturbance from the experimenter. Three distinct drained stress ratios were studied for pseudo-isotropic, K 0, and highly deviatoric loading paths. The results indicate that the K 0 path shows the most uniform deformation mechanism, where the measured ratio of deviatoric and volumetric strain increments reaches the stress ratio applied at boundary value level for large magnitudes of total strain. The pseudo-isotropic test also reaches a strain ratio close to η at large total strain levels, however, the deformation field is less uniform. Furthermore, the highly deviatoric stress path shows the most heterogeneous deformation fields commensurate to the applied stress ratio, though the ratio of deviatoric and volumetric strain increments fell above the η applied. The mean value of the 3D spatial fields of strain corresponds well with the changes observed at boundary level, supporting prior research on drained stress-probing on clays for which there is no 4D deformation data available.
... et al., 1990) In order to study the properties of pore distribution and accurately describe the change of relative content of different size pores, it is necessary to classify the pores. However, there is no unified standard for the boundary value of pore size division of soft clay and sludge (Delage and Lefebvre, 1984;Griffths and Joshi, 1989;Hua yang et al., 2009;Lapierre et al., 1990). Shear et al. (1992) conducted a large number of experiments based on undisturbed and reconstituted specimens of soft gray Pleistocene clay, and classified According to the pore division standard above, the volume percentage content of each pore' type was calculated, as shown in Fig. 13. ...
The spacing of PVDs is an essential factor affecting the consolidation effect of vacuum preloading. For exploring the influence of spacing of PVDs on the impact of sludge drainage consolidation, FeCl3, a commonly used inorganic coagulant, was used to pretreat the sludge. In the experiment a vacuum filtration test was carried out to determine the optimal addition amount of FeCl3, and then the landfill sludge was pretreated according to the FeCl3 optimal addition amount. And two different spacing of PVDs were used to carry out a vacuum preloading contrast test. Then, the drainage and settlement were recorded, and water content and vane shear strength (VSS) were measured after the experiment. Finally, Mercury intrusion porosimetry (MIP) was carried out to explore the pore characteristics of the sludge further. The main conclusions are as follows: After conditioning by FeCl3, the sludge’s flocculent structure was destroyed, the intracellular water was released, and the effect of drainage capacity was significantly improved. After the spacing of PVDs is halved, the average volume reduction ratio and shear strength increases, and the effect of advanced dewatering and volume reduction of sludge improved significantly, leading to a better consolidation effect. In the progress of vacuum drainage consolidation, halving the spacing of PVDs results in large pores transformation into small pores, and the range of drainage consolidation is greatly expanded.
... Some studies have shown that there is a certain relationship between porosity, strength, and fracture energy (Rice 1989;Sun et al. 2016). Therefore, a significant amount of research has been conducted on the pore characteristics and pore size distribution of soil at room temperature or low temperatures by means of scanning electron microscopy and the mercury injection test (Lapierre et al. 1990;Sasanian and Newson 2013;Zhang et al. 2015a, b). Changes in temperature alter the pore structure and porosity of rocks and soil (Knapp and Knight 1977;Nishiyama and Yokoyama 2017). ...
Soil protection is a critical issue in the UN Sustainable Development Goals (SDGs). In this light, understanding the changes in the micropore structure of loess—which have a great influence on its macroscopic physico-mechanical properties—is crucial. Temperature is one of the main factors affecting the porous structure of loess; to ascertain the effects of high temperatures on the porous distribution of loess, Malan loess was sampled from the Shaanxi Province of China. The changes in porous characteristics of the loess samples after being subjected to high temperatures were tested using a non-destructive method—nuclear magnetic resonance (NMR)—and the tensile failure load of the loess at different temperatures were obtained. The results show that NMR can be used to characterize the variations in loess pores with temperature. In general, the porosity of loess decreases with increases in temperature. For temperatures above 600 °C, the pore radius begins to increase with increases in temperature; further, pore connectivity is improved at high temperatures, between 200 °C and 800 °C. The tensile failure load of loess not only increases exponentially with increases in temperature, but also there is an exponential relationship between porosity and tensile failure load.
... Based on the Poiseuille's equation for laminar flow through a capillary tube, the hydraulic conductivity for a distribution of capillary tubes (kc) having different diameters di can be expressed as (Lapierre et al., 1990): ...
A pre-compacted MX80 bentonite/Callovo-Oxfordian (COx) claystone mixture has been proposed as a candidate sealing material in a French deep geological repository for high-level radioactive waste. An in-depth understanding of the hydraulic property of this material is essential for accessing the over-pack corrosion and nuclide migration along the gallery. In this study, water flow in the compacted bentonite/claystone mixture was investigated by carrying out infiltration and water retention tests under constant-volume conditions alongside detailed microstructure observation. The evolution of total water hydraulic conductivity with suction was experimentally determined based on the instantaneous profile method. It was observed that the measured total hydraulic conductivity increased slowly at high suctions, then quickly at low suctions and finally approached the saturated value. A new method was developed based on the evolving pore structure, accounting for both vapour and liquid-water hydraulic conductivities. The total hydraulic conductivity predicted by the proposed method agreed well with the measured value, indicating the reliability of the predictive method. The vapour hydraulic conductivity was larger than the liquid-water one at a suction larger than 15·2 MPa, while liquid-water hydraulic conductivity became dominant at a suction lower than 15·2 MPa. In addition, based on the predicted vapour and liquid-water hydraulic conductivities, a numerical model was set up to simulate the water infiltration process. Comparison between the simulation and the measurement showed close agreement, validating the two-phase water flow mechanism in the bentonite/claystone mixture.
... Several theories have been proposed to correlate permeability with pore size distribution [30], [31]. Studies conducted by [32] show that permeability is a direct function of PSD. PSD obtained through mercury intrusion contributes to the interpretation of critical behavioural characteristics of unsaturated soils. ...
In highly porous soils with a susceptibility to collapse, there are points of volumetric variability, due to the present heterogeneity, regarding the diameters of the poral throat. The predominance of a pore size is closely related to certain values of the Water Retention Curve (WRC). However, to date, a possible correlation with particle size distribution (PaSD), obtained using modern, highly reliable gravitational sedimentation methods, has not been studied. The porous clay of lateritic origin under study, was characterized by means of index tests, to know its basic geotechnical behavior. Subsequently, it was analyzed by mercury intrusion porosimetry tests, to estimate the Pore Size Distribution (PSD); filter paper and pressure plate method to obtain the water retention curve; as well as the method of integral measurement of the pressure in the suspension (ISP), to obtain the fine grain size of the material. This article tries to present a proposal of relationship between these parameters, with the aim of improving the understanding in the characterization of this type of materials. The results showed that there is indeed a strong relationship between the particle size distributions, pore size distribution and the water retention curve. Mainly, this is reflected in the geometric places corresponding to the air value entries (AEV) of macropores and micropores. Which coincide with essential parameters of the behavior of the other curves (PaSD and PSD).
... PoreMaster 60 [26] 10 /m 1.5% 2.5% 5% 5% dV/dlg(d)/(mL g 1 ) 5% 5% ...
This paper studies the improvement mechanism of loess soil modified by the consolid system in
comparison with the loess soil modified by cement and lime. The mechanical strength test，disintegration test and
flexible-wall permeability test were conducted to measure the engineering property of soil. The water drop
penetration time test，X-Ray diffraction test，scanning electron microscope(SEM) test and mercury intrusion
porosimetry(MIP) test were carried out to investigate the microscopic properties，such as the surface energy，
mineral composition，microstructure and pore filling condition of loess soil. The loess soil modified by the
consolid system has higher strength，better durability of slaking and slightly lower permeability. The surface energy of soil particles is reduced greatly and the water repellency ability is obviously better than that of cement or lime modified loess soil. The phase peak groups are basically same in the X-ray diffraction patterns. The silt particle arrangement of loess soil remains unchanged with the increase of consolid system content，but the fineparticles coagulate with more adhering material. The volume of large，medium and small pores in loess soil are
reduced slightly while the micro pores are increased obviously. The improvement mechanism of loess soil
modified by consolid system is that the decrease of surface energy of loess soil enhances the water repellency and
water-resisting property，the consolid system reinforces the bonding strength of the microstructure of soil particle skeleton，the weak swelling and pore filling effect of consolid system lead to good permeability of loess soil. Apart from improving the mechanical and hydraulic properties，the consolid system solve the problem of improving the water resistance property and keeping the good permeability of loess soil to some extent.
Key words：soil mechanics；loess soil；consolid system；engineering properties；modified
... In clay-rich caprocks, chemical reactions tend to have smaller effects due to preferential flow paths and minimal pore surface area exposure (e.g. Lapierre et al., 1990;Yang and Aplin, 1998;Amann-Hildenbrand et al., 2013). Super-critical CO 2 can react with organic matter in mudrocks, causing changes in pore structure (Busch et al., 2008), although little organic content can be observed in the A and B shales on CT scans and the bulk density of the preserved shale (2.53 g/cc) is consistent with low organic content. ...
Geological storage of carbon dioxide (CO 2) is a long-discussed strategy for avoiding CO 2 discharge into the atmosphere and a few industrial scale projects are underway in this regard. In order to successfully perform such a strategy, it is important that site evaluation takes into account both reservoir and caprock properties in order to trap the CO 2. Many caprocks for such sites are clay-rich mudrocks, hence evaluating their seal capacity and seal integrity are critical for storage sites. Analytical studies on the impact of potential CO 2-water-rock interaction are an important part of site evaluation since potential geochemical reactions may degrade the seal quality and effectiveness. This paper investigates the impact of static exposure of mudrock seals to super-critical CO 2 (sCO 2) at high temperature and pressure (150 C, 29 MPa) on the mineralogy (illite-smectite, kaolinite, illite and quartz), major element geochemistry and geomechanical properties of mudrock seals over a six-month period. Mineralogy and geochemistry were determined stepwise from their preserved initial state and after 1, 4 and 6 months exposure to sCO 2 in a batch reactor, with no detectable changes in any of the minerals or elements observed. This is likely due to low reactivity in silicate systems and low volume of pore fluid available to facilitate chemical reactions. Samples for geomechanical testing were exposed to sCO 2 for 6 months only. Geomechanical properties changed significantly between preserved and sCO 2 exposed samples tested under equivalent effective stress conditions, with sCO 2 exposed samples being much stronger and stiffer than their preserved counterparts. Given that no mineralogical and geochemical changes were noted during exposure to sCO 2 , it is most likely that the loss of pore water during sCO 2 exposure resulted in the strengthening and stiffening of these mudrocks.
... The sizes of macro pores, medium pores, fine pores and micro pores are about 80-700 lm, 2-80 lm, 0.08-2 lm, and 0-0.08 lm, respectively. According to Lapierre et al. (1990), mercury intrusion porosimetry measures entrance pore diameter. It cannot measure the inside diameter of pores because it assumes that pore shape of soil is cylindrical. ...
This experimental study investigates the consequences of one-dimensional consolidation pressure on the macro and micro soil structure during the reconstitution process of marine clay as well as to determine the effect of pressure on the soil structure generated due to material self-weight at the lower portion of fillings. For this research, soft marine clay is selected, and specimens are reconstituted with low percentages of cement. The clay-cement slurries are consolidated under 98 kPa and 50 kPa vertical pressure with the drained condition. The consequences of consolidation pressure on macro and micro structure are determined by performing the oedometer tests, scanning electron microscope analyses, and mercury intrusion porosimetry tests. It is noted that consolidation pressure has a significant effect on the structure of marine clay concerning void ratio, compression index, yield stress, and pore size distribution. The total pore volume decreases with increasing the consolidation pressure as well as the medium pores larger than 1 μm also decreases and converts into fine and micro pores having the size among 1μm–0.01 μm.
... That is why permeability prediction with mercury intrusion data is a unique interdisciplinary approach. Lapierre et al. [16] showed that there is a relationship between the pore-size parameters and the permeability of the clay. Al Hinai et al. [17] correlated permeability with capillary pressure from mercury intrusion measurement. ...
The mercury intrusion technique is a crucial in-lab method to investigate the porous medium properties. The potentiality of mercury intrusion data has not been explored significantly in the traditional interpretation. Thus, a hierarchical statistical model that not only captures the quantitative relationship between petrophysical properties but also accounts for different geological members is developed to interpret mercury intrusion data. This multilevel model is established from almost 800 samples with specific geological characteristics. We distinguish the fixed effects and the random effects in this mixed model. The overall connection between the selected petrophysical parameters is described by the fixed effects at a higher level, while variations due to different geological members are accommodated as the random effects at a lower level. The selected petrophysical parameters are observed through hypothesis testing and model selection. In this case study, five petrophysical parameters are selected into the model. Essential visualizations are also provided to assist the interpretations of the probabilistically model. The final model reveals the quantitative relationship between permeability and other petrophysical properties in each member and the order of relative importance for each property. With this studied relationship and advanced model, the geological reservoir simulation can be greatly detailed and accurate in the future.
... As the SWCC at high suction ranges represents the micropores in soil, the variations in the initial void ratios would not change these micropores corresponding to the high suction levels. In addition, the works of Griffiths and Joshi (1990), Lapierre et al. (1990), Miao et al. (2007), Oualmakran et al. (2016, Sun and Cui (2017), and Li et al. (2018) showed that micropores were not compressed even when the applied load was large enough to destroy the interaggregate pores. As a result, it can be assumed that when the soil is subjected to compression (due to a mechanical load or suction load), the pores are compressed from the large pores to the small pores. ...
The soil-water characteristic curve (SWCC) contains information regarding the geometric pore space in a soil and it is commonly used to estimate the unsaturated soil properties such as unsaturated hydraulic conductivity and unsaturated shear strength. It is also noted that soil volume change can significantly affect the SWCC and engineering properties of soil. Different SWCCs can be obtained if the soil specimens are prepared with different initial void ratios. The volumetric shrinkage curve (VSC) is commonly used to convert SWCC in the form of gravimetric water content (w-SWCC) into a curve that is in the form of degree of saturation (S-SWCC). In this paper, a framework is developed, in which different S-SWCCs are generated based on the measured w-SWCC of soil in a relatively loose condition and the VSC. The proposed framework is based on the concept of pore size distribution function (PSDF). The estimated SWCCs corresponding to different initial void ratios from the proposed framework were verified by using the experimental data from published literatures.
... However, because the structural mass is microscopically a porous medium composed of soil particles of different sizes, these models do not represent actual behavior, and vary in significance with stress-strain trajectories. Each component of a single pore distribution is representative of a specific suction curve [21], this theory has incidence in the prefiguration of a constituent archetype that relates both permeability and relative suction. The general concept of the theory of percolation was proposed by [22], to understand the stochastic field of random means linked to the network models that symbolize the porous tissue of the geotechnical volume, and that are complementary to the theory of filtration. ...
In geotechnical structures, the permeability-dependent stability analysis is generally evaluated under vertical trajectories, because most permeameters are configured so that the water passes through the porous medium in this way. However, it is clear from the physical point of view that water can flow along different paths, including preferential ways that can include horizontal trajectories, parallel to the deposit of the stratum. The foregoing implies that both the vertical and horizontal component of the hydraulic conductivity or permeability coefficient must be estimated for a given stratum. The current research aims to explore possibilities for measuring the coefficient of permeability in horizontal trajectories, on granular soils, under a constant condition of relative density. For this purpose, a special chamber attached to a constant head permeameter was designed and constructed, which allows to measure the permeability in conditions of horizontal flow parallel to the soil layers. The proposed camera also admits the estimation of the permeability coefficient by combining stratifications of different granular soils, where the trajectories are not perfectly horizontal, but have diagonal paths. The results are compared with data obtained by conventional vertical flow permeameters, in order to check the difference in the measurements considering both situations in the samples. As a conclusion, it is important to report that there is evidently a difference in the permeability coefficients measured under different trajectories
... Several studies have been https://doi.org/10.1016/j.coldregions.2020.103037 Received 28 April 2019; Received in revised form 1 February 2020; Accepted 12 March 2020 performed to investigate the microstructure changes in swelling rocks and soils due to remoulding and climatic conditions (Delage and Lefebvre, 1984;Lapierre et al., 1990;Delage, 2010;Aldaood et al., 2014;Burton et al., 2015;Hotineanu et al., 2015;Zeng et al., 2018;Niu et al., 2019). Delage and Lefebvre (1984) found that remoulding affected the inter-aggregate links but did not destroy the aggregates when the researchers examined the microstructures of intact and remoulded Champlain Sea clay using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. ...
The pore structure governs the physical and mechanical behaviours of geomaterials, thereby affecting the stability of the infrastructures built on these materials. This study investigated the effects of remoulding and wetting-drying-freezing-thawing (WDFT) cycles on the pore structures of two Yanji mudstones using scanning electronic microscopy (SEM), mercury intrusion porosimetry (MIP) and nitrogen adsorption (NA) techniques. The results show that the pores of both the yellow-brown and magenta mudstones become rounder and more disordered after remoulding. Remoulding leads to an increase in the inter-aggregate pore volume and a decrease in the intra-aggregate pore volume because of the exposure of intra-aggregate pores after crushing and the compaction of aggregates during the compression process. The W-D-F-T cycles make the pores of the remoulded yellow-brown mudstone more disordered and flatter and induce an increase in the inter-aggregate pore volume due to the formation of cracks and large pores. Meanwhile, the intra-aggregate pore volume decreases owing to the contraction of aggregates during the drying process. According to the increased inter-aggregate pore volume and decreased intra-aggregate pore volume, an increase in the hydraulic conductivity and a decrease in the shear strength can be expected after remoulding and W-D-F-T cycles, which decrease the stability of mudstone slopes.
... us, it is of significant importance to study the SWCC of the loess. e soil-water characteristic is influenced by many factors [10,11], such as mineral composition, soil structure, dry density, stress history, the drying, and wetting circulation. e microstructure is the most fundamental factor while other factors work mainly by changing the microstructure of the soil. ...
Soil-water characteristic curve (SWCC) is a key constitutive relationship for studying unsaturated soil, and as is known, microstructure of the soil has great influence on the mechanical behaviour of the soil. In this study, the wetting and drying soil-water characteristic curves (SWCCs) of loess compacted at three different water contents were measured using the filter paper method. And microproperties of compacted loess were obtained by the mercury intrusion method (MIP) and scanning electron microscope (SEM). Results show that the compaction water contents have significant influence on the SWCC and microstructure. The pore size distribution (PSD) curves have great differences in macropore range and are similar in micropore range. Loess compacted at optimum and dry of optimum are generally connected, while there are certain number of nonintruded pores in loess compacted at wet of optimum. The SWCC curves vary significantly in low suction ( ua − uw < 1000 kPa) and tend to converge together in high suction ( ua − uw ≥ 1000 kPa). Hysteresis in the SWCCs is more obvious for loess compacted at optimum and dry of optimum in the matric suction of 0∼100 kPa; however, there is a pronounced hysteresis for loess compacted at wet of optimum in full matric suction range. The characteristic of the SWCCs including their hysteresis can be well interpreted from the loess microstructure.
... The order of magnitude of the inter-platelets bonds within the aggregates is obviously stronger, since they are not affected by remoulding, that keeps their intra-aggregates pores intact. This observation that the elementary microstructure unit involved, but not destroyed, by remoulding is the aggregate has also been made in Lapierre et al. 9 who adopted the same methodology on another eastern Canada sensitive clay (Louiseville), and has recently been confirmed on a Swedish sensitive clay (Utby) by Birmpilis et al. 10 , based on an investigation conducted by using Small Angle X-ray Scattering (SAXS) and Digital Image correlation techniques (DIC). Fig. 3 also shows that the aggregates did not resist to drying, that resulted in significant shrinkage, as shown by the much smaller intruded volume and average pore diameter. ...
Based on long term investigations of the microstructure of various geomaterials as different as sensitive low plastic clays from Eastern Canada, unsaturated compacted silt from the Paris area, highly plastic
compressible deep marine clay from the gulf of Guinea, compacted MX80 bentonite and the Callovo–Oxfordian claystone, considered as possible barriers in deep geological radioactive waste disposal, two
fundamentals and distinct nano and micro mechanisms governing their macroscopic volume changes have been identified. In low plastic structured clays and dry compacted soils, in which an aggregate
microstructure has been evidenced, the decrease in volume under mechanical compression result from the collapse of inter-aggregates pores in an ordered manner, from the larger to the smaller, with no effect on the intra-aggregate porosity. The soil skeleton can hence be modelled as an elastic fragile porous matrix, affected by the ordered collapse of its pores. Things are different in plastic soils, due to the significant reactivity of the montmorillonite minerals to changes in water content that results in significant changes of the initial porous matrix. The ordered adsorption of layers of water molecules in clay platelets with respect to the suction or stress applied, evidenced long time ago in Soil science through X-ray diffraction techniques, appear to be able to help better understanding various phenomena like the compression of plastic compressible soils and the hydration of compacted bentonites. Interestingly, it also applies to understand the effects of smectite minerals in the volume changes behaviour of the Callovo–Oxfordian claystone. These two mechanisms at nano and microscopic scales hence provide a better understanding of the macroscopic volume changes of a large variety of natural and compacted clayey soils and rocks.
... [12] 模型 和 Hardin-Drnevich 模型 [13] 、Ramberg-Osgood 模型 [14] 以及 Martin 和 Seed [ Martin 和 Seed [15] 其后在 Dvidenkov 模型基础上提出了携带形状参数 的经验公式(1-9)。 黄雨等 [55] 称形状参数 为"阻尼比的增长率"参数且不受固结压力的影响，认为绝大数 土处于 在 0.2~1.2 之间并取上海软土为 1.0。 陈存礼等 [56] 对西北粉质黄土试验研究决定 [62] ，于是对此进行了修正。孙静、袁晓铭等 [65][66][67][68] [144] 岩石裂缝分形理论，Katz 和 Thompson [145] 的岩石孔 隙渗透性研究以及大量石油工程关于孔喉研究内容 [146] 。对于细粒土的微观研究方面， [147] 就提供了一整套完整的常见 沉积矿物衍射值。Gillott [148] 在此基础上计算 Leda 黏土的 X 射线衍射峰值面积以确定组 构指数来研究黏土矿物含量。在我国 X 射线衍射试验先后大量运用于地质科学、岩土工 程的研究当中，例如谭罗荣等 [149,150] 对湛江黏土原状土和重塑土进行 X 射线衍射试验， 采用强度比例因子法研究其矿物成分。我国还在相应的研究基础上制定了相关行业规范 1[151] 以确定沉积矿物种类及含量。 扫描电子显微镜是揭示沉积物颗粒与孔隙排列和组构的绝佳手段，该试验方法出现 后立刻作为研究细粒土微观特性的重要研究方式。Sergeyev 等 [152] 将早期 Gillott [153] 、 Barden 和 Sides [154] 、Tovey [155] [164] 、雷华阳等 [165] 、孟庆山等 [166] 、李榴芬等 [167,168] 均作出相关工 作。 孔隙度测量法选用非湿润性流体来研究孔径的分布，该分布对多孔介质的渗透性、 变形性的性能有关，汞作为良好的试验材料开始逐步替代水用于毛细压力的孔隙度测量 法。 压汞法早期用于石油工程的孔喉尺寸、 分布以及饱和度的研究起着至关重要的作用， 以决定孔隙结构的储集层(石油油层)的产能。例如 Pittman [169] 对于最小孔喉比所对应 汞饱和度用于评价油层产液水平。而在细粒土研究方面，压汞法自从被 Diamond [170] 用 于研究黏性土的孔径后开始被其他学者大规模采用。除了 Griffiths 和 Joshi [171] 、Lapierre 等 [172] 、Penumadu 和 Dean [173] 等大量对传统黏性土的孔径研究外，Romero [174] 、Simms 和 Yanful [175] 等开始将压汞法用于非饱和土的研究当中，Aldaood 等 [176] 则将其运用于土 的冻融循环土研究中。国内研究者中自压汞法作为优秀的孔隙度测量法以替代水压法之 后，石油勘探早期研究 [177,178] 逐步活跃。近些年随着页岩储油层研究 [179,180] ，压汞法以 及改进压汞法等相关技术重新得到重视。谢和平和钱平皋 [181] 是国内较早将压汞法运用 在岩石力学的研究。王清等 [182] 是较早开展压汞法与分形几何学结合以研究土中孔隙分 布。谭罗荣 [183] 在雷祥义 [184] 对陕北黄土的压汞研究与渗透性关系的基础上根据孔隙的形 状对多孔介质材料压汞法结果进行修正。 此外， 特殊土如膨胀土的孔隙分布特征研究 [185] 以及类似吕海波等 [186] 、薛茹 [161] 对细粒土沉积物尤其是软土的压汞法研究也展开相关工 作。 上述按照试验方法分类的细粒土微观研究多是建立在单一试验手段下，合理运用多 种试验的联合微观试验研究工作更能全面的反映研究对象的结构与组构。Gillot [187] 归纳 X 射线衍射对沉积矿物的判别加上扫描电子显微镜下各沉积矿物的组构方式与形态学 研究算是联合微观试验法的典范。Osipov [188] 总结了诸如光学显微镜、扫描电子显微镜、 透射电子显微镜以及 X 射线衍射的联合微观结构研究手段， 对比了各方法下的优缺点及 适用条件，为今后显微镜手段对黏性土研究的介入提供依据。Remoro 和 Simms [ [191,192] 在采用环境扫描电子显微镜和能谱仪 EDX 技术结合，对上海饱和软黏 土的原状土和重塑土微结构和矿物成分进行分析，最终通过能量法建立微观力与宏观力 的关系以及微观变形转为宏观应变的关系，其中模型中接触面弹性应力应变符合 Hertz-Middlin 弹性法切向理论。周晖、房营光等 [193][194][195] 对广州地区软土在固结下进行环 境扫描电子显微镜和压汞研究。在表达颗粒定向性方面，适当引入施斌 [196] 对于土体单 元排列的概率熵 m H ，反映土微观结构单元体的排列有序性。王婧、莫海鸿等 [197][198][199] [203] 最早开展了以 PI=7(Plasticity Index)作为界限将中间介质土分 为"似砂土行为"土和"似黏土行为"土，分类的原则是由于前者为应力或应变失效而后者 为循环软化失效。Bray 和 Sancio [204] 对典型中间介质土的动力性能进行试验分析，改用 黏土矿物的塑性指数用于判别液化灵敏度而不是采用传统的黏粒组含量百分比。Saglam 和 Bakir [205] 采用泥浆沉降(Slurry Deposition)制样方法，对中间介质低塑性粉土重塑后 进行单轴压缩和动扭剪三轴试验，同时对动强度的多种影响因素进行讨论。类似的研究 还包括 Wijewickreme 团队关于多种尾矿 [206,207] 以及河道沉积物 [208] 的液化判别研究工 作。 国内天然中间介质土的动力微观研究则更多关注砂粒与黏粒的角色担当问题。阮永 芬和巫志辉 [209] 采用六偏磷酸钠作为分散剂对饱和粉土动力特性进行研究。认为粉土的 骨干曲线服从双曲线规律但受到黏粒含量影响严重，这与马德翠等 [210] 对黄河三角洲粉 质土的动模量与阻尼比研究结论一致。给出的解释是由于粉土强度由两部分组成即黏粒 的胶结和砂粒的内凝聚力及摩擦力。黏粒存在有阻碍粉土发生液化的可能性，这是由土 体的结构性原因导致的 [211] 。王兰民、邓津等 [ [235] 与 Ochoa-Cornejo [236] 同时瞄准了锂皂石这种纳米级的水中凝胶物质对传统砂土进行抗液化改造，当然在锂皂 石改造土的试验方法和微观机理研究上两派学者为此还进行了激烈的讨论 [237,238] (2) 比表面积的测定采用乙二醇乙醚吸附法 [289] (Ethylene Glycol Monoethyl Ether) ， EGME 为吸附质测定，保持一定 EGME 蒸气压，使得 EGME 分子以单分子的形式吸附 ...
The quaternary marine fine-grained soil is the main sedimentary layer of Guangdong typical estuary delta (i.e. the Pearl River Delta and the Han River Delta). Traditional soil classification method is based on the weight percent of particle size, which can not reflect the engineering characteristics of fine-grained soil. The relative ratio of clay minerals and non-clay minerals in fine-grained soil is a determinant in Atterberg’s limits of soil classification. Besides, fine-grained soil particles and microscopic characteristics of the sedimentary minerals affect the macroscopic mechanical behaviors of soil under both the static load conditions and dynamic loading conditions such as strength, deformation, pore water pressure and dynamic stability. According to the research background of formation process of quaternary marine fine-grained soil in Guangdong typical estuary deltas, mineral composition and dynamic behaviors of remolded sediments are analyzed and the results show significant influence of sedimentary mineral composition on the dynamic behaviors, which were lack of thorough research. Based on the sedimentary mineral quantification, reliable energy analysis method is used to discuss dynamic behaviors including dynamic strength, dynamic deformation, dynamic pore water pressure and viscosity property. Meanwhile, pore structure characteristic by mercury intrusion porosimetry and microscopic structure characteristic by environmental scanning electron microscope are combined for microscopic characteristic analysis. Finally, dynamic behaviors and microscopic characteristics are successfully related and bridged, a pioneering attempt of interdisciplinary study of engineering geology, soil dynamics and micromechanics.
The main research contents and conclusions of the thesis are presented in the following.
(1) With reference to the weight percentage of main sedimentary minerals in the marine fine-grained soil sediments, pure minerals such as quartz, albite, sodium montmorillonite and kaolinite are used to remold marine fine-grained soil sediments. The reliable microstructure morphology of reconstructed samples provides conditions for subsequent dynamic behavior and microscopic characteristic researches.
(2) Energy dissipations are separated into viscous property energy dissipation, plastic strain energy dissipation and elastic strain energy dissipation by energy-based method and the calculation models of accumulated energy dissipation are proposed. The viscous energy dissipation ratio（VEDR） is established in analogy to viscoelastic equivalent damping ratio. In addition, to cope with the lag of pore water pressure, the hysteretic pore water pressure energy dissipation ratio（HPWPEDR） is given based on the relationship between relatively effective pore water pressure and cyclic stress.
(3) According to the growth rate relationship between viscous property cumulative energy dissipation and plastic strain cumulative energy dissipation, dynamic modes of fine-grained tailing soil and sedimentary mineral soil are reclassified as four categories: stable type, stable damage type, damage type and collapse type with consideration of three dynamic phases, i.e., cyclic compaction or looseness, cyclic shear, and cyclic damage. Energy-based method explains the transitional and mutational failure mode of intermediate soil. Combined with effective stress path based characteristic lines, critical values of shear strains are determined in accordance with relevant microscopic mechanism. Meanwhile, the existing energy-based pore water pressure models are further developed to predict the time-history curve of pore water pressure.
(4) Because of high clay minerals content (more than 50%) in sedimentary mineral soil, alternative growth rates between viscous property cumulative energy dissipation and plastic strain cumulative energy dissipation are not obvious. Furthermore, the weakly bound water transfer into free water film under approximate cyclic stress ratio is limited in sedimentary mineral soil group. Thus, integral relative slippage provided by free water is restricted, and the influence of the limit free water on the intergranular stiffness decreases. When weight ratios of sedimentary minerals and related plastic index change, clay mineral relations group has more significant influences on accumulated energy dissipation, attenuation of dynamic secant shear modulus, viscous property energy dissipation and hysteretic pore water pressure energy dissipation than non-clay mineral and clay mineral relations group.
(5) The influence of internal energy change mechanisms during cyclic loading on dynamic behaviors such as dynamic deformation, dynamic pore water pressure and viscosity property is analyzed for soils including fine-grained tailing soil and sedimentary mineral soil. VEDR mutation criterion is established to distinguish the dynamic strength. The critical strain amplitude of the VEDR mutation point, different from small threshold strain, is another important threshold of the transition from moderate strain to large strain. And the traditional one-to-one correlation of the plastic index influence on engineering and dynamic behavior is found to be not applicable to sedimentary mineral soil.
(6) Two microscopic characteristic parameters that show the pore structure and microscopic structure are coordinated in three aspects of porosity and void ratio, pore size and distribution and pore stratification and connectivity. This coordination demonstrate the reliability of the combined micro test method. In the end, microscopic dynamic behavior analysis method is preliminary put forward based on three sets of dynamic behavior parameters and microscopic characteristic parameters—critical strain amplitude and pore direction probability entropy, Davidenkov model parameters and perimeter-area fractal dimension and pore size distribution fractal dimension, and HPWPEDR and sandbox-counting fractal dimension.
... It follows that the orientation of the micro-REV fabric does not increase in 1D compression from medium to very high pressures, differently from what assumed in the literature (e.g. Morgenstern and Tchalenko, 1967;Tchalenko, 1967;Delage and Lefebvre, 1984;Lapierre et al., 1990;Hicher et al., 2000;Hattab et al., 2013). Furthermore, at C*, the same as at A*, the fabric within the micro-REV is still not uniform, as evident at large scale (example of local randomly oriented fabric in Figure 7b). ...
The letter describes an investigation of the microstructural features of a high-plasticity clay, in both its natural conditions and reconstituted in the laboratory. Scanning electron microscopy is used here to characterise the fabric at different magnification, while image processing of the micrographs delivers a quantitative assessment of the fabric orientation. Results of Energy dispersive X-ray spectroscopy and swelling tests, as reported in previous work by the authors,
are used to characterise the bonding nature and strength, as well as mercury intrusion porosimetry to investigate the clay porosimetry.
Despite their identical composition, the natural and the reconstituted clay have experienced different deposition and loading history, generating different microstructural features that are shown to underlie their differences in state. For both clays, 1D compression to medium-high pressures is seen to determine a well oriented medium magnification fabric. However, larger scale observations and the corresponding image processing results reveal non-uniform local
fabric features, hence making fabric characterisation dependent on the scale of analysis and bringing about the issue of identifying the clay micro-scale representative element volume relating to the clay macro-behaviour. The micro-REV is identified for the clays under study and its connection with the macro-behaviour characterized.
The microstructural evolution induced by 1D compression to very high pressures is shown to concern mainly the clay porosity and
porosimetry, the fabric orientation being steady, thus explaining the isotropic hardening observed in laboratory tests.
... As well known, the intrinsic permeability of clays (e.g. Mesri & Olson, 1971;Tavenas et al., 1979;Lapierre et al., 1990) is a function not only of the flow direction and void ratio, but also of the clay micro-to meso-scale porosimetry, the tortuosity and shape of the pore channels, and the clay mineralogy. Furthermore, the impact of the adsorbed water, held in the diffuse double layer, on the water flow through the micropores, may evolve depending on local physical−chemical conditions. ...
The letter discusses about the relation of the coefficient of saturated permeability in a given direction, ki, with the void ratio, e, for fissured and unfissured clays, where ki characterizes the hydraulics of the equivalent uniform porous model. The ki – e data for the fissured clays are compared with what is observed for unfissured clays, either natural, or reconstituted. For each clay, the ki - e data result from laboratory investigation and are related to the fissuring identity of the clay, F-ID, classified through a fissuring characterization chart. Through such procedure, the study provides an initial rational insight of the variability of the ki – e law with both the micro and the meso-scale clay features. Fissuring is shown to cause meso-scale non uniformities of the flow patterns, which may cause a variation between the ki for steady state seepage and that controlling transient seepage. In general, fissuring increases the clay permeability, not only with respect to that of the same clay if unfissured, but also with respect to the same clay when reconstituted. Also, the study sheds light on the difference between the ki – e law holding during compression and that during swelling for both unfissured and fissured clays, showing that such difference is more important for fissured clays.
The swelling pressure of the bentonite bufers plays an important role in the design of deep geological nuclear waste repositories. The present article highlighted the swelling behavior of Na-monovalent and Ca-Mg divalent Indian bentonites in
isochoric (constant volume) and free swelling conditions. Constant volume swelling pressure tests and one-dimensional free
swelling strain tests were conducted on the bentonites with an initial specimen dry density of 1.6 Mg/m3
. The pore size distribution (PSD) and morphological changes of bentonites in free swelling and isochoric swelling conditions were examined
through MIP and FESEM tests. The results showed that in the free swelling condition, the monovalent bentonite exhibited
a higher swelling strain (126.2%) and a higher water absorption capacity (107%). On the other hand, the exerted swelling
pressure and water absorption capacity of divalent bentonite (4.34 MPa, 36.1%) were found to be higher as compared to
monovalent bentonite (1.42 MPa, 31.4%) in isochoric conditions. It indicates that the phenomenon of free swelling characteristics is diferent from the swelling pressure measured in isochoric conditions. The MIP and FESEM images showed that
the hydration phenomenon caused a signifcant decrease and increase in macropores volume of bentonites in isochoric and
free swelling conditions, respectively, especially for monovalent bentonite. However, micropore volume was noted to be
increased and decreased marginally for isochoric and free swelling conditions, respectively. The free swelling phenomenon
of the bentonites depends on the type of exchangeable cations and mineralogy. In isochoric conditions, along with cations
and mineralogy, the swelling pressure depends on the PSD of bentonites.
Resulting from the preferential alignment of sediment particles, permeability anisotropy of unconsolidated strata is an essential parameter for natural gas hydrate (NGH) exploitation. Fundamentally, the effect of mineral particle shape and pore-filling NGH on the permeability anisotropy are considered in this study. A simulation with combining methods of particle flow code and computational fluid dynamics is conducted to construct a series of numerical samples and calculate the anisotropic permeabilities. Different particles shapes and hydrate saturations are preinstalled in these samples. It is firstly proved that the elongated particles have little effect on permeability anisotropy. Meanwhile, the preferential alignment of plate-shaped particles is the main reason for permeability anisotropy. In principle, the difference between intermediate orthogonal axes and short orthogonal axes of plate-shaped particles makes the tortuosity different in directions, thus inducing the permeability anisotropy. The anisotropy ratio decreases with the increase of hydrate saturation, which is caused by the nonlinear decline of main channel flow resulting from the thrombus-like hydrate particles. The results provide an insight into the formation mechanism of permeability anisotropy and display potential application value in NGH exploitation, groundwater environment protection and geological disaster prevention.
This paper presents a new 3D mathematical pore network model for evaluating some important, but hard-to-measure physical properties, including permeability, relative permeability, recovery factor, and sealing capacity from easy-to-measure mercury intrusion data. A 3D pore network is constructed by mimicking the penetration process of mercury based on an idealized pore shape. The pore shape is two frustra of cones connected at their base. A pore orientates in 3D space with an alignment angle to the bedding, which is a function of deformation of the sedimentary rock. Since mercury intrusion measures a 3D pore network and intrudes pores from largest to smallest, a pore size distribution measured by mercury intrusion is itemized into individual pores; a 3D pore network model is then formed by adding pores, one by one from the largest to the smallest, to the pore network. In the process, pores are connected into pore strings along the three orthogonal directions. The properties are derived by modeling fluid flow in the pore strings in a particular direction. Sealing capacity is simply the capillary pressure of the smallest pore of the first three largest orthogonal pore strings of the 3D pore network. Permeability is modeled by applying the modified Hagen-Poiseuille equation, Darcy’s law, energy and mass conservation, and the effect of eddy formation and flow direction change in the pores to the constructed 3D pore network model. Relative permeability is modeled for the imbibition process for two-phase flow based on the below imbibition theory proposed in this paper. Initially, the nonwetting phase exists in large pore strings, and the wetting phase occupies small pore strings. There are always some pores in a large pore string connected with pores of the small pore strings. In the imbibition process, under the differential pressure and capillary pressure, the wetting phase in some small pores invades some large pores filled with the nonwetting phase at the contact to form interfaces. As a result, in these pore strings, the effective pressure drop, which drives the movement of the fluids, is reduced by the capillary pressure of the interfaces. The constructed relative permeability model is a function of viscosity, interfacial tension (IFT), and contact angle of the fluids, and also pressure gradient, which is often overlooked. The developed model has been applied to some mudstone and limestone samples. The modeled sealing capacities of 29 mudstone samples show that a mudstone with a clay content greater than 40% and porosity less than 0.2 would be an effective caprock to oil. The modeled permeabilities of 29 limestone samples show that the model is able to predict limestone permeability within a factor of two in nearly four orders of magnitude range. The modeled relative permeabilities of two limestone samples demonstrate the effect of IFT, contact angle, and pressure gradient on the relative permeability and recovery factor and the capability of the model to simulate a special phenomenon—permeability jail.
The microporosity structure of a soil provides important information of hydraulic conductivity and soil–water characteristics of the soil, as described in Chaps. 3 and 5. The microporosity structures of fine soils may change significantly during wetting and drying (Simms and Yanful, Can Geotech J 38:741–754, 2001; Cuisinier and Laloui, Int J Numer Anal Meth Geomech 28:483–499, 2004; Boivin et al., Soil Sci Soc Am J 68:1145–1153, 2004; Braudeau et al., Soil Sci Soc Am J 68:359–370, 2004). Such variations of soil microporosity structures are inherently related to the drying and swell/shrinkage behavior of the soil (Ferber et al., Eng Geol 104:200–210, 2009; Aung et al., Geotech Geol Eng 19:401–416, 2001) and are the main difficulty in establishing quantitative relations between soil fabric and soil shrinkage/swell behavior.
An investigation of clay microstructure and its evolution under 1D and isotropic compression is presented for different clays. Data from the literature are compared to original results on two Italian clays, obtained using SEM, image processing, MIP and on-purpose swelling tests. The effects of composition and loading history on clay microstructure, as well as its changes along the compression path (pre- and post-gross-yielding) are analysed and a conceptual model of microstructure evolution is proposed for the clays under study. NC clays at early virgin compression, either natural or reconstituted, are found to possess an open fabric of random-low orientation, complying with a prevailing inter-aggregate and a smaller intra-aggregate porosity, whose size and distribution depend on composition. Under 1D compression, either in the field or in the laboratory, the inter-aggregate porosity is lost, at a rate dependent on composition and loading history, and the dominant intra-aggregate micro-pore is progressively reduced. Accordingly, perfectly oriented stacks of domains are recognised which, though, embed preserved random particle arrangements even at large pressures, resulting in an increase of average orientation up to the reach of a steady orientation degree. Isotropic compression causes faster microstructure evolution, although large pressures are required to change 1D-induced fabric orientation.
The study highlighted the fabric evaluation (i.e., pore size distribution (PSD) and morphology) of monovalent and divalent Indian bentonites, subjected to different suctions and consolidation pressures. Oedometer tests were conducted on bentonites specimens in two different initial conditions, i.e., slurry and compacted conditions. The slurry and compacted specimens were prepared at water contents equal to liquid limit (LL) and optimum moisture content (OMC), respectively. The water retention properties of the bentonites were determined in both unconfined (slurry) and confined (compacted) conditions using pressure plate apparatus and WP4C dew-point potentiometer. The influence of different consolidation pressures and suctions on pore structure and morphology of the bentonites were investigated by mercury intrusion porosimetry (MIP) and Field Emission Scanning Electron Microscope (FESEM) observations. For both the bentonites, the bimodal pore size distribution was observed over the applied consolidation pressure between 7.2 kPa and 2289.6 kPa in both slurry and compacted specimen conditions. However, an increase in consolidation pressure lead to a significant decrease in macropore volume. The compression index of the bentonites was found to be strongly correlated with a percentage decrease in macropore intruded volume (R² = 0.91) and total intruded pore volume (R² = 0.89), however, independent of micropores volume. The FESEM images and MIP results evidenced that for both the bentonites more homogeneous morphology and effective filling of the pores took place in slurry conditions as compared to initially compacted specimens. For the same void ratio, the hydraulic conductivity of slurry specimens was noted to be slightly lower than the compacted specimens. In slurry conditions at suctions below 3 MPa, the water retention capacity of monovalent bentonite was noted to be higher than that of divalent bentonite, whereas the opposite trend was found in compacted conditions. Irrespective of slurry or compacted conditions, the increase in suction lead to the transformation of bimodal PSD into a unimodal pore family for divalent bentonite, whereas trimodal to unimodal PSD was noted for monovalent bentonite in compacted specimens. The initial state (slurry or compacted) and the boundary condition of the specimen, as well as fabric (pore size distribution and morphology) of the bentonites, were found to have a notable influence on the compressibility, hydraulic conductivity and water retention properties.
The key to maintain the stability of the excavation face of slurry shield in the construction of high-permeability circular-gravel stratum is the film-forming quality of slurry. Taking the use of slurry shield in the construction of Nanning Metro in circular-gravel stratum as a case, and with the help of self-designed slurry permeation device, this paper carries out the permeation film-forming experiments of different ratios of slurry in circular-gravel stratum to study the effects of slurry specific gravity, viscosity, and grouting pressure on amount of infiltrated water, film-forming time, and slurry film shape and carries out a verification at the construction site. The conclusions are as follows: slurry specific gravity increases linearly with the content of clay, and the viscosity increases linearly with the content of CMC. The higher the slurry specific gravity is, the better the film quality is. The higher the slurry viscosity is, the earlier the slurry film is formed and the smaller the amount of water infiltrated from slurry is. The effect of slurry specific gravity on the amount of infiltrated water is greater than that of viscosity. The field verification results show that when the slurry density is 1.07 g/cm3, the slurry film has been basically formed, and when the mud density is 1.15 g/cm3, the slurry film has been formed completely. When the slurry viscosity increases from 24 to 33 s, the liquid level of the air cushion chamber and the number of air compressors change slightly. When the water loss of the slurry is 14 s, the slurry level of the sedimentation tank changes slightly, and slurry loss is effectively controlled; when the viscosity of the slurry increases and cause water loss to reaches 12 s, the viscosity of the slurry achieves the optimal effect. This study can provide reference for studies of similar projects in the future.
Cement treatment is a promising and effective method to enhance strength of calcareous sand in regions where offshore foundations and coastal facilities are localized. In treatment, the added cement content and curing period influence the strength of cemented calcareous sand. In order to regulate the loading resistance of cemented calcareous sand, effects of cement content and curing period on strength enhancement are investigated experimentally. First, cemented specimens with 5%, 7.5%, and 10% cement contents and 1–28 days curing period are prepared. Then, unconfined compression test is conducted to measure strength. Nuclear magnetic resonance test is also performed to analyze microstructure change during hydration reaction. An empirical equation of strength is derived, considering the effects of cement content and curing period. This equation shows higher accuracy than existing empirical models. In addition, the microstructure change in hydration process is quantified by pore volume evolution. Void ratio is used to characterize the pore volume evolution. Hence, the dependence of strength on cement content and curing period is quantitatively explained by the change in void ratio. This sheds light on hydration reaction in cement treatment by cement content and curing period and the regulation of strength enhancement in cemented calcareous sand.
• Highlights
• Empirical equation on strength with effects of cement content and curing period
• Pore volume evolution by hydration reaction in cement treatment
• Characterization of microstructure change by void ratio
• Microscopic mechanism of strength enhancement for cemented calcareous sand
The microstructure properties of soft clay in Shanghai were discussed in light of experimental observations from a series of triaxial stress path tests and field emission scanning electron microscope (FESEM) tests performed on undisturbed soft clay specimens. The microstructure changes of soft clay were observed during different stress paths tests. The microstructure parameters were analysed by fractal geometry theory. The results show that the mechanical properties of soft clay are subject to the effect of stress paths, variations in initial confining pressure, which are controlled by its microstructure. Shanghai soft clay is manifested by a typical skeleton microstructure with large pores and flat laminated clay particles. The total volume and number of pores increase, and the distributions of soil aggregated particles and pores become looser due to loading; thus, the void ratio and fractal dimensions of the pores and soil particles are positively correlated with the axial strain. They reveal that cementation between the soil particles decreases and that the microstructure of soft clay is damaged by not only pore enlargement, but also degradation of the soil particles. Damage onset, damage development and failure occur during the entire process of soft clay subjected to triaxial loading. The microstructure parameters affected by reduced triaxial compression (RTC) tests change to a larger degree than those affected by conventional triaxial compression (CTC) tests, indicating that there is weaker cementation between the soil particles in the RTC tests due to the stress path and negative pore pressure generation. The microstructure evolution of natural soft clay during loading can be used to analyse the macro-mechanical behaviours.
Multiple consolidation-permeability tests were performed on loess samples from the South Jingyang Plateau in northwest China to analyze permeability under actual stresses. Three-dimensional microstructures for loess samples under each consolidation stress were established based on high-resolution computed tomography images to thoroughly interpret the permeability variation in terms of the loess microstructures including the pores and throats. With increasing consolidation pressure, the permeability decreased greatly at the beginning and tended to become stable. In the stage of dramatic decrease in permeability, pore coordination number decreased slightly under pressure, indicating little influence of connectivity among pores on permeability. The pores in the range of 14 to 25 μm decreased by 10.1% in volume percentage, and the pores larger than 13 μm decreased by 19.6% in number. Accordingly, throats larger than 6 μm decreased by 13.1% in area percentage, and throats larger than 2 μm decreased by 14.9% in number. Throat size distribution played a decisive role in permeability, pore size distribution acted as a bridge to influence permeability, and only the spaced pores and some interaggregate or intergrain pores larger than 13 μm that allowed free water to pass were related to permeability. The decreases in these relatively large pores and throats caused considerable decreases in permeability. However, the existence of large throats, even large numbers of such throats, does not mean high permeability, which can be verified in the stable stage of permeability. This research provides a better understanding of loess permeability in terms of three-dimensional microstructure and further insights into the stability analysis of loess slopes and the control of other hazards in loess regions.
p>Microbial biopolymers are introduced as a new soil binder which regarded to be environmentally-friendly materials in terms of low carbon emission and low impact on the soil ecosystem. In geotechnical engineering and agriculture, various gel-type materials have been used to improve the water absorbability of sandy soils, and control surface erosion. In this study, the soil-water characteristics of xanthan gum biopolymer-treated sand-clay mixtures are evaluated through a laboratory program using a soil-water characterization apparatus. Sand-clay mixtures are treated with different xanthan gum concentrations as 0% (untreated), 0.1%, 0.25%, 0.5%, 0.75% and 1.0%, to the mass of soil, respectively. Consequently, the xanthan gum-soil water characteristic curve results show the enhanced water holding capacity of soils with higher xanthan gum contents. The presence of xanthan gum hydrogels in the soil increases the initial and residual water contents. Biopolymers retain moisture loss from the soil, which makes the slope of the soil-water reduction curve to be more gradual.</p
Carbonation of reactive magnesia (MgO) has recently received increasing attention in the area of soil stabilization and ground improvement. However, as a critical parameter in terms of long-term seepage behavior in the geotechnical analysis, the hydraulic conductivity of carbonated reactive MgO-stabilized silt has not been fully studied. In this context, the effect of water-MgO ratio (ratio of initial water content to MgO content, w0/c) and carbonation time on hydraulic conductivity (or permeability) characteristics was systematically investigated. Serial microstructural tests including mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses were applied to elucidate the intrinsic mechanisms. The obtained results indicate that as the initial water-MgO ratio decreases, the void ratio gradually decreases and the reduction of hydraulic conductivity becomes less prominent because of the little presence of flow paths. The hydraulic conductivity of carbonated MgO-admixed silt similar to that of PC-treated silt is mainly governed by the porosity, and its correlation with void ratio is proposed in the article. The variations of permeability with void ratio are consistent with those of the cumulative pore volume from MIP results in general, and the medium pores (3–30 μm) are substantiated to be the primary contributor in controlling the permeability. SEM and DSC analyses reveal that the cementation of soil particles and filling of hydrated magnesium carbonates marginally reduce the voids and permeability. The reasons for changes of permeability behaviors have been confirmed by the pore-size distribution and microstructure characteristics.
With the advent of new methods of soil microstructure determination and related constitutive models, it has become more important to interpret macroscopic phenomena such as water flow in porous medium based on soil microstructure properties. The main purpose of this paper is to review the history of research on the effect of microstructure on hydraulic conductivity of saturated and unsaturated soils. After a brief overview of the main microstructural characterization methods, the two most commonly used methods, mercury intrusion porosimetry and scanning electron microscopy, are evaluated in more detail. In particular, the detail, the relative advantages and disadvantages of these methods along with the results of indexed studies are covered. The hydraulic conductivity coefficients of saturated and unsaturated soils are discussed, focusing on its direct influence on the microstructural properties of the soils. In the end, suggestions for future research in this area are presented.
Soil permeability is an important parameter for assessment of infiltration, runoff, ground water, drainage and structures design. In the current research, five different data driven algorithms namely Multilayer Perceptron (MLP), Co-Active Neuro-Fuzzy Inference System (CANFIS), Support Vector Machine (SVM), Decision Tree (DT) and Random Forest (RF) algorithms and also, their wavelets (W-MLP, W-CANFIS, W-SVM, W-DT and W-RF algorithms) were used to predict soil permeability based on physical properties of soil. Also, reliable information/input vectors were assessed based on Gamma Test (GT). Sand, silt, clay and organic content (OC) parameters were chosen as information vectors based on gamma test. The potential of data driven algorithms were evaluated based on different statistical indices during model development and validation phase. It was found that wavelet based algorithms viz. W-MLP, W-CANFIS, W-SVM, W-DT and W-RF simulated better results of soil permeability compared to non-wavelet (MLP, CANFIS, SVM, DT and RF) algorithms. Among all wavelet and non-wavelet algorithms, W-RF algorithm had the highest accuracy and efficiency of model. The results of sensitivity analysis indicated that clay > silt > sand > OC > BD > PD was the order of sensitive parameters for soil permeability prediction based on data driven algorithms.
Abstraet-A knowledge of the distribution of pore sizes in clay and soil bodies is a useful element in the microstructural characterization of such materials. Pore-size distributions and total porosity of a number of reference clays, naturally-occurring subsoils, and commercial clay samples prepared in various ways were determined by mercury porosimetry. The range of equivalent pore diameter explored covered almost five orders of magnitude, from several hundred microns down to approxi- mately 150A. The method and its assumptions are critically evaluated, and measurements of the contact angle of mercury on clays yield values of 139 ~ for montmorillonite and 147 ~ for kaolinite and illite clays. The extent of shrinkage on oven-drying prior to mercury intrusion is assessed in each case and found to vary from insignificant to as much as 30 per cent of the pore space, depending on microstructural state and degree of initial saturation. The development of techniques for water removal which do not involve change in pore structure is explored. Some preliminary results for structurally weak saturated clays suggest that critical-region drying and perhaps freeze-drying procedures may be practical.
The cryoscan is an apparatus equipping the JEOL scanning electron microscopes, and allowing the observation of freeze-fracture planes of samples whose temperature is maintained below −100 °C. The application of this method to a sensitive clay from Quebec shows an aggregated structure, the aggregates being separated by 1 μm size voids.
Describes the use of quantitative mineralogy and specific surface area in interpreting the index properties of clayey soils from nine sites in E Canada. Samples representative of the Tyrrell, Laflamme, Champlain, and Goldthwait marine seas and Lac Barlow-Ojibway have been studied. Correlations between Atterberg limits and specific surface area are believed to be more useful than those between specific surface area and the grain size or clay fraction. The mineralogical composition of the soils studied is dominated, even in the clay fraction, by felsic minerals (plagioclase, quartz, microcline, and hornblende). -from Authors
SEM and mercury intrusion porosimetry are used in parallel to identify the structure of a medium sensitivity Champlain clay. The clay structure is observed firstly on intact, remolded, and over-dried soils and secondly on soils consolidated at various levels in one-dimensional compression. Both methods of investigation reveal for the intact soil the existence of an aggregated structure characterized by an interaggregate and an intra-aggregate porosity. Remolding affects interaggregate links but does not destroy aggregates. The observation of clay structure at various levels of one-dimensional compression shows that the collapse of the structure is progressive, the largest interaggregate pores being the first affected.-from Author
Permeability tests were performed on materials of differing grain size and shape of gradation. It was found that permeability was primarily dependent on and was practically independent of the shape of gradation for the range of materials tested. Key words: permeability, tests, laminar flow, sand, gravel, particle gradation.
This investigation utilizes pore size distribution measurements to examine the relationship between permeability and compactive variables for laboratory compacted clayey silts. Closed-system falling head permeability tests under back pressure were performed on each of the compacted samples. Freeze drying was successfully used to dehydrate specimens prior to pore size measurements. The mercury intrusion technique was used to determine the pore size distribution. The pore size distributions of the soils tested were bimodal with a large pore mode occurring between 10 ? and 1 ? and a small pore mode occurring at 0.1 ?. Varying the compaction variables produced changes in the size and frequency of the large pore mode, but caused no change in the pore size distribution about the small pore mode for a given soil type. Three theoretical permeability models that relate pore size distribution parameters to permeability were generated. These parameters were successfully used to determine empirical permeability prediction equations for the soils tested.
Flows through porous media are reviewed, discussing the properties of a porous medium, equations and boundary conditions. Our attention is focussed on flows of viscous fluid through porous channels, tubes, past a porous cylinder and sphere, between rotating disks filled with porous materials, and on propagation of waves in a porous medium.
The permeability, of a porous material to water is a function of the geometry of the boundary between the solid component and the pore space. Expressions of the Kozeny type purporting to represent this function are based upon the particle size or specific surface of the solids, and whilst, for engineering practice, they have given satisfaction for saturated sands, they may fail badly in other cases. By developing a Kozeny type of expression for the particular structure of a bundle of capillary tubes of assorted radii, we demonstrate the cause of the failure. Such failure may be avoided by relating permeability to pore-size distribution, which is the factor of prime concern and which may be measured directly by even simpler means than are used to determine particle-size distribution. The pore-size distribution is arrived at by an interpretation of the moisture characteristic of the material, i.e. of the curve of moisture content plotted against pressure deficiency. A simple statistical theory, based upon the calculation of the probability of occurrence of sequences of pairs of pores of all the possible sizes, and of the contribution to the permeability made by each such pair, leads to an expression of the permeability as the sum of a series of terms. By stopping the summation at a selected upper limit of pore size one may calculate the permeability at any chosen moisture content and plot it as a function of that content. An example is presented, using a coarse graded sand specified by its moisture characteristic. To check these calculations, experimental determinations of the permeabilities of unsaturated materials are presented, using two different grades of sand and a sample of slate dust, the results being compared with computed values. The agreement seems good, and is certainly better than that provided by the Kozeny formula as developed, with difficulty, for the purpose. The limitations and possible improvements of our concept are very briefly discussed, and finally it is shown how a combined use of the moisture characteristic and the permeability (which is itself derivable from the moisture characteristic) leads to an expression for the coefficient of diffusion of water in the material as a function of moisture content. From this it should be possible, in principle, to calculate in suitable cases the course of water movement down a gradient of moisture content. Such a calculation awaits a satisfactory solution of the problem of non-linear diffusion.
The factors. (1) possible violations of Darcy’s law. (2) electrokinetic coupling. (3) high viscosity. (4) tortuous flow paths, an. (5) unequal pore sizes have been suggested as possible explanations for the differences between hydraulic flow rates in liquid-saturated clays and sands. The effects of these factors on hydraulic flow rates through saturated clays were investigated.
Hydraulic flow rates, electrical conductivities, and streaming potentials were measured on natural, sodium, and calcium samples of kaolinite, illite and Boston blue clay. Data were taken after increments of one-dimensional consolidation and rebound over the pressure range from one-sixteenth to 256 atm.
The influences of electrokinetic coupling on the hydraulic flow rates were calculated from irreversible thermodynamic relationships together with the hydraulic and electrical data. The other factors were studied by examining the extent to which each factor explains the discrepancies between measured flow rates and those predicted from Darcy’s law and the Kozeny-Carman equation.
The results show that. (1) the possible violations of Darcy’s law and electrokinetic coupling are insignificant. (2) high viscosity and/or tortuous flow paths fail completely to account for the discrepancies between measured and predicted flow rates in clays, an. (3) unequal pore sizes can explain all the discrepancies.
A quick clay soil from a site close to the Grande‐Baleine River on the west bank of Hudson Bay has been resedimented artificially. Specimens were formed at salinities of 0.2 and 35 g/L to simulate freshwater and marine environments. Under a consolidation pressure of 50 kPa, the specimens were shown to yield sensitivities from 5 to 26, the highest being for the low‐salinity specimens. The natural sensitivity (as measured with the fall cone) is greater than 300.The initial compressibility of soils formed at low salinity is lower than those at high salinity, but values at higher pressures converge with the compressibility of the intact soil. The sensitivity of the artificial soil is lower than that of the intact soil and reflects the greater structuration of the latter. For artificial soils, the sensitivity increases as the salinity decreases; this is due mostly to a reduction in the remolded strength.Results show that freshly deposited soils can have a high void ratio that results from a structuration or resistance of the soil skeleton. Such aspects as compressibility and the plasticity‐sensitivity relationship are also discussed.
There have been only a few direct investigations of clay compression at the microlevel. This Note presents the preliminary results of an investigation of the microstructural changes due to consolidation of four clays, each stressed to four levels in one-dimensional consolidation, freeze-dried and analysed using mercury intrusion porosimetry.
Studies of the pore size characteristics and permeability of compacted sandy soils are described. Samples of mixtures of Ottawa sand and kaolinitic clay were prepared by kneading compaction and pluvial compaction was used to prepare samples of a clean Ottawa sand. The pore size distributions (PSD) of the samples were determined by mercury intrusion porosimetry, and the permeability of each sample was measured by a falling head test with back pressure. A pore size density function was derived from the PSD data. For the sand specimens, this function showed a singly modal characteristic on a log diameter scale while those of the sand-clay mixtures showed bimodal characteristics. The influence of varying water content and compactive effort on the fabrics of the soils studied could be readily characterized by changes in the resulting pore size distributions and density functions. A probability-based permeability model which relates the pore size density function to the permeability of compacted soils was verified experimentally.
Synopsis
Estimates of permeability of the ground are frequently required by civil engineering work involving the seepage of water. Several published formulae relating the permeability of beds of granular material to their geometrical properties are quoted. In order to assess the value of these formulae in calculating permeability, a comparison is made between measured and calculated values of permeability for a wide range of sands.
Hazen's formula is quite useful because of its simplicity but the result may be inaccurate to the extent of ±2. Kozeny's formula is the best of those quoted, and if an estimate of the “angularity” of the grains is made, permeabilities of sand can be computed to an accuracy of about ±20 per cent. An empirical formula is given which is equally accurate and more simple to use. Computations of permeability by the methods described can be made only on clean sands.
Pour les travaux de génie civil relatifs à des infiltrations d'eau, il est souvent něcessaire de faire 1'èvaluation de la perméabilité du sol. L'on peut citer plusiers formules qui ont été publiées relatives à la perméabilité des couches de matières granulaires selon leurs propriétés géométriques. Pour pouvoir évaluer la valeur de ces formules dans les calculs de perméabilité, on a comparé les valeurs de la perméabilité obtenues par calcul et par mesure sur une variété de sables.
La formule d'Hazen rend de grands services à cause de sa simplicité mais le résultat en peut être inexact dans la mesure de ±2. Parmi les formules citées, la meilleure est celle de Kozeny et si l’on fait une évaluation de 1”' angularité” des grains, les perméabilités du sable peuvent eêtre évaluées dans les limites de ± 20 per cent environ. II existe une formule empirique qui est exacte au m±me degré et qui est plus simple à employer. Les calculs de perméabilité par les méthodes décrites ne peuvent êêtre faits que sur des sables propres.
Seven series of tests have been performed on specimens from five natural soft clay sites to determine the variation of the vertical and horizontal permeabilities when the soil is unidimensionally compressed. The results show that the permeability anisotropy does not increase significantly with compression up to strains of 25% for marine clays. In varved clays, mostly because the clay laminae are more compressible than the silty laminae, the anisotropy increases with vertical compression. Key words: permeability, clay, anisotropy, laboratory, compression.
The permeability characteristics of a number of intact natural soft clays from Québec, the USA, and Sweden have been investigated in the laboratory. The variation of permeability with void ratio is best represented in terms of a linear e vs. lg k relation which is generally valid in the range of volumetric strains encountered in engineering practice.The permeability at the in-situ void ratio is shown to be a complex function of such parameters as the void ratio, the clay fraction, the plasticity index, and the fabric of the clay. Permeability anisotropy is negligible in marine clays.The e vs. lg k relationships of the various clays tested are well ordered in terms of an empirical parameter (IP + clay fraction), irrespective of the geological origin of the clay. The slope of the e vs. lg k relationship, referred to as permeability change index Ck, is simply related to the initial void ratio by Ck = 0.5eo. Keywords: permeability, clays, laboratory tests, permeability anisotropy, permeability – void ratio relations.
The methods of measuring the permeability of clays in the laboratory are investigated. Constant head tests in the triaxial are best suited for testing large specimen under field stress conditions provided the cell is modified to eliminate leakage. Using this type of test, the validity of Darcy's law is confirmed.Falling head tests in the oedometer are very simple to perform and subject to minimal sources of errors. However, small size specimens may not be totally representative.Indirect evaluations of the permeability from consolidation tests are shown to be unreliable particularly in structured natural clays: evaluation of k from cv measurements in step-loaded tests gives much too low values, constant rate of strain tests strongly overestimate k in the vicinity of σp′ and give nonrepresentative e vs. lg k relations; controlled gradient tests tend to underestimate k at all void ratios. Keywords: permeability, clays, laboratory tests, test equipment, consolidation tests.
The relationship between soil fabric and the anisotropic consolidation characteristics of a sensitive, highly flocculated marine clay has been studied using x-ray diffraction techniques. Measurements of the clay particle parallelism (fabric) were performed on “undisturbed” and remoulded samples of Leda clay from Ottawa, Canada, in an attempt to determine the influence of sample disturbance on soil fabric and laboratory consolidation test results.The amplitudes of the 10 Å clay peaks of the “undisturbed” natural clays, measured in the major principal plane, increased from about 11 counts/second at low consolidation pressures to about 40 counts/second at 64 tons/sq. ft. This is interpreted as resulting from reorientation of many of the clay platelets into the plane perpendicular to the direction of the consolidation pressure. An abrupt reorientation occurred when the pre-consolidation pressure was exceeded.Remoulding the clay apparently causes a marked breakdown of the interparticle bonds as evidenced by stronger 10 Å peaks and inferred greater particle parallelism at any given consolidation pressure within the range studied. This increase in parallelism is associated with a pronounced reduction in void ratio when compared with the “undisturbed” clay.
An equation has been derived for the relation between permeability and the size distribution of the pores in isotropic material. If the mean radius of the pores in each of n equal fractions of the total pore space is represented in decreasing order of size by r1, r2., and rn cm. respectively, then permeability is given by
where is the porosity in cm.3/cm.2 of porous material, and K is in units of cm.2 By this means, permeability can be calculated from she curve relating water content to suction. This has been tested on published data for flow of air through porous stones and flow of water through saturated and unsaturated sands. Calculated values have been found to agree satisfactorily with measured values over a wide range of permeability.
The Kozeny equation is discussed as a particular case of this equation
Mathematical interpretation of the pore size disribution (PSD) data as measured by mercury intrusion porosimetry was revealed in detail. The PSD data were commonly presented as cumulative intruded volume per gram of specimen versus pore size. In this paper, however, they were expressed in a dimensionless term for convenient mathematical operations. The pore size density function was deduced from the PSD data using the finite difference approximation and curve-fitting technique. For the prediction of permeability, first the published correlations between permeability and pore geometry were critically reviewed. A probabilistic permeability model based on the pore size density function was then developed, which can be thought of as a generalization of Childs and Collis-George's model. Predictions of permeability of the compacted soils studied using the developed model were very good for a wide range of permeabilities.
Thèse (Ph. D.)--Université de Sherbrooke, 1982. Comprend une bibliogr.
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