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Influence of temperature variation on soil behavior
... Based on both the pioneering work of Campanella and Mitchell (1968) and the 121 critical analysis presented by Coccia and McCartney (2016), the current 6 122 framework identifies three possible mechanisms responsible for the thermal 123 volume change of saturated soils. The first mechanism, thermal primary 124 consolidation, is associated with a time-dependent volumetric contraction of the 125 soil as the pore water pressure generated by the increase in temperature dissipates. ...
... Current studies have sought to explain this 135 phenomenon by assuming that physicochemical interactions govern the processes 136 at the microscale. Campanella and Mitchell (1968) suggested that a decrease in 137 the shear strength of inter-particle contacts occurs as temperature increases and 138 that this phenomenon should end when new bonds are developed to carry the 139 induced stresses. In addition, according to Laloui and Rotta Loria (2019), the 140 physicochemical interactions contributing to this phenomenon appear to be (i) the 141 degradation of the adsorbed water layer caused by an increase in temperature 142 (Fleureau 1979;Pusch 1986), (ii) the variations in the rigidities of the mineral 143 involved, which modify the contact force network (Kingery et al. 1976), and (iii) 144 the modifications of the equilibrium between the Van der Waals attractive forces 145 and the electrostatic repulsive forces (Laloui 2001). ...
... In these cases, the thermal volume change 158 was mainly associated with the effects of pore water dissipation. In the tests 159 conducted by Campanella and Mitchell (1968), Baldi et al. (1991), Hueckel and 160 Pellegrini (1996), and Cekerevac and Laloui (2004), the volumetric strain of the ...
Understanding the behaviour of soil-structure interfaces is critical for addressing the analysis and design of energy geostructures. In this study, the interface failure mechanism of energy piles (where a shear band is detached from the surrounding soil that behaves under oedometric conditions) is experimentally analysed in laboratory for saturated conditions. The choice of material (clayey soil and concrete), temperature range, and stress level is based on conditions that are likely to be encountered in practice. Specifically, cyclic thermal tests under constant vertical effective stress in oedometric conditions as well as constant normal stiffness (CNS) interface direct shear tests (in which samples have been subjected to thermal cycles between 10 and 40 °C) are presented. From a practical perspective, the results show very low volumetric strain variations and negligible effects on shear strength. The volumetric aspects do not appear to have significant impact on the shear resistance of the interfaces against cyclic thermal loads. Fundamental insight on the effects of thermal cycles on the concrete-soil interface behaviour which are relevant to energy piles are presented. In addition, the proposed interpretation procedure provides a basis for the standardisation of thermomechanical testing in geotechnical engineering.
... Several studies have been performed in full or laboratory scales to investigate the effect of temperature on mechanical behavior of energy geostructures. From in-situ thermomechanical testing of energy piles (Laloui et al. 2006;Bourne-Webb et al. 2009;Murphy et al. 2015;Faizal et al. 2018) to advance laboratory testing of soils at non-isothermal conditions (Baldi et al. 1988;Campanella and Mitchell 1968;Ghahremannejad 2003;Burghignoli et al. 2000;Lahoori et al. 2020). The following mechanical aspects of the soils are discussed in this section: ...
... The internal layer of water close to clay mineral is known as adsorbed layer and the surrounding water is double layer water (Fig 1.5). Thermal strains in saturated clays result from the thermal expansion of clay mineral, rearrangement of the clay skeleton structure, water behavior, and drainage conditions (Campanella and Mitchell 1968). Due to the electrochemical interactions between solid surface of minerals and surrounding water four types of pore water exists: (i). ...
... In normally consolidated clays under drained conditions soils the thermally induced contraction during heating and subsequent cooling is irreversible. Subsequent thermal cycles, produce smaller increments of irreversible deformation (Baldi et al. 1988; Campanella and Mitchell 1968;Ghahremannejad 2003;Burghignoli et al. 2000;Cekerevac and Laloui 2004;Towhata, Kuntiwattanaku, Seko and Ohishi 1993;Abuel-Naga, Bergado, Bouazza and Ramana 2007;Delage et al. 2000). In highly overconsolidated soils (OCR>2) the heating causes an expansion and subsequent cooling causes a contraction which is totally reversible. ...
Incorporation of heat exchangers in conventional geostructures like piles can extract the heat from the soil for heating purposes and inject it to the soil for cooling purposes. In recent years, research has been conducted at full and laboratory scale to investigate the effect of temperature on the geotechnical behavior of these energy geostructures as well as on the surrounding soil. Indeed, these energy geostructures can be subjected to cyclic mechanical loads and thermal variations throughout their lifetime. The aim of this study was to deepen the understanding regarding the behavior of sand/clay-structure contact under complex thermo-mechanical loads. A temperature-controlled direct shear device to perform monotonic and cyclic constant normal load or constant normal stiffness tests was developed. The response of the interface to the thermal effects on the mechanical behaviour of soils and soil-structure interface was investigated. Fontainebleau sand and kaolin clay were used as proxies for sandy and clayey soils. The results showed that the applied thermal variations have a negligible effect on the shear strength of the sand and sand-structure interface. In clay samples the temperature increase, increased the cohesion and consequently the shear strength, due to thermal contraction during heating. The adhesion of the clay-structure interface, was less than the cohesion of the clay samples. To investigate the mechanical cyclic load effects on the clay-structure interface at different temperatures, monotonic and cyclic constant-volume equivalent-undrained direct shear tests were performed on clay-clay and clay-structure interface at different temperatures. The results showed that, the number of cycles to failure for the clay-structure interface test was lower than that for the clay-clay case in the same range of cyclic and average shear stress ratios. Increasing the temperature, decreased the rate of strain accumulation and the number of cycles to failure increased by 2-3 times. The rate of degradation (degradation parameter, t) decreased by 16% with heating from 22 to 60oC for the different cyclic stress ratios tested. A non-isothermal soil-structure interface model based on critical state theory was then developed. The non-isothermal model takes into account the effect of temperature on the void ratio of interface prior to shearing. The model is capable to capture the effect of temperature on soil-structure interface under constant normal load and constant normal stiffness conditions for both sandy and clayey interfaces. The additional parameters have physical meanings and can be determined from classical laboratory tests. The formulation is in good agreement with the experimental results and the main trends are properly reproduced.
... However, the volume change of the clays in the undrained thermal mechanical loading conditions cannot be neglected and does not hold constant due to the thermal expansion of the clay mass . This expansion has a crucial importance in undrained heating analysis as shown by some researchers (Campanella and Mitchell, 1968;Khalili et al., 2010). Formally, undrained condition for both isothermal and non-isothermal evolutions should refer to evolutions under constant mass of water condition. ...
... The main features of temperature effects on undrained saturated clays are first briefly analyzed. Then, the thermo-hydro-mechanical equations proposed by Campanella and Mitchell (Campanella and Mitchell, 1968), Lewis and Schrefler (Lewis and Schrefler, 1987) and Coussy (Coussy, 2004) are recalled, compared and discussed, showing the compatibility and difference among them. Afterwards, the thermohydro-mechanical elasto-plastic constitutive formulation under undrained condition for saturated clays is presented in the framework of TEAM model. ...
... At critical state, no further excess pore pressure develops. Campanella and Mitchell (Campanella and Mitchell, 1968) initiatively gave the expression for pore water pressure variation along thermo-mechanical loading paths under undrained condition using a simple governing equation for the volume change of total clay mass. Lewis and Schrefler (Lewis and Schrefler, 1987) combined the mass balance equation with Darcy's law for the liquid phase in the pore space of porous media under non-isothermal condition. ...
... Drainage conditions play an important role in most geotechnical problems, so it does under thermal load. Undrained heating generates excess pore water pressure (PWP) significantly (Abuel-Naga et al., 2007a;Campanella and Mitchell, 1968;ESRIG, 1969;Hueckel and Pellegrini, 1992;Tanaka et al., 1997) due to the thermal expansion of water. The magnitude of thermally induced pore pressure can reach more than 50% of the preconsolidation pressures in normally consolidated (NC) samples when subjected to 50°C elevation, while the overconsolidated (OC) specimens experience less increase (Abuel-Naga et al., 2007a). ...
... The magnitude of thermally induced pore pressure can reach more than 50% of the preconsolidation pressures in normally consolidated (NC) samples when subjected to 50°C elevation, while the overconsolidated (OC) specimens experience less increase (Abuel-Naga et al., 2007a). Theoretical analysis (Campanella and Mitchell, 1968) concluded that the rate of pore pressure increase depends highly on soil compressibility. Thermally induced excess PWP can be detrimental to soil with initial deviator stress q, because it draws the stress state closer to the critical state line (CSL). ...
... After the temperature fully recovered from the first TH state, the soils were believed to be more densified and reached a lower void ratio represented by the point Y in Fig. 12 (b). Theoretical analysis (Campanella and Mitchell, 1968) indicated that the magnitude of thermal induced pore pressure directly linked to the porosity. There would be less pressurization in soils when heated after the thermal cycle and this was supported by the cyclic thermal lab-experiments (Bai and Su, 2012). ...
Thermomechanical behaviour of clay has been widely investigated by well-controlled laboratory experiments, while in-situ test of thermal effects on soil is rare. The piezocone penetration test (CPTU) is first used in this study to directly evaluate the temperature effects under in-situ stress condition. A full-scale precast high strength concrete (PHC) pile was utilized as the heat source and a series of CPTU were conducted in adjacent layered clays after monotonic heating and thermal cycle. The results show that unprecedented temperature elevation leads to an apparent reduction of soil strength in all soil layers; this degradation was alleviated after the thermal cycle. After exposure to a higher temperature, the normally consolidated soil was improved even when tested at a lower elevated temperature; whereas, the overconsolidated soil could nearly recovered to the pre-heated value. The measured pore pressure (u2) also decreased after heating indicating a more overconsolidated or dilatant behaviour during shearing. By comprehensively considering the in-situ responses, the in-situ soils were believed to be unloaded by the thermally induced pore fluid pressurization and densified after cyclic thermal loading. Finally, a hypothesis is proposed to qualitatively explain the thermomechanical responses of in-situ soil in the framework of critical state soil mechanics theory.
... This interest is driven by several energy-related applications, including heat storage (Baser and McCartney 2015;Başer, Lu, and McCartney 2016;Burger 1985), oil and gas drilling (Dusseault, Wang, and Simmons 1988), and heat exchanger or energy piles (Abdelaziz, Olgun, and Martin 2015;Abdelaziz 2016;Abdelaziz and Ozudogru 2016a, b;Batini et al. 2015;Chen and McCartney 2017;Jaradat and Abdelaziz 2018;Knellwolf, Peron, and Laloui 2011;Olgun, Abdelaziz, and Martin 2012;Xiao, Suleiman, and McCartney 2014). Several studies focusing on understanding the thermomechanical behavior of soils are reported in the literature (Alsherif and McCartney 2012;Baldi, Hueckel, and Pellegrini 1988;Burghignoli, Desideri, and Miliziano 2000;Campanella and Mitchell 1968;Cekerevac and Laloui 2004;Coccia and McCartney 2016a;Hueckel and Baldi 1990;Houston, Houston, and Williams 1985;Hueckel and Pellegrini 1992;Uchaipichat and Khalili 2009;Uchaipichat, Khalili, and Zargarbashi 2011). Most of these studies relied on modifying conventional triaxial cells to facilitate controlling the specimen temperature. ...
... During undrained heating/cooling, thermally induced pore water pressures are generated in the soil specimens because of differences in the thermal expansion coefficients of the soil particles and the pore water (Campanella and Mitchell 1968;Ghaaowd et al. 2017;Kuntiwattanakul et al. 1995;Mitchell and Soga 2005;Tanaka, Graham, and Crilly 1997). The thermally induced pore water pressure, measured using the pore water pressure transducer shown in figure 1, includes the temperature effects on the system and the expansion/contraction of the water in the drainage lines. ...
... The normally consolidated clay specimen used in this study experienced thermoplastic (i.e., irrecoverable) contractive volume changes (see fig. 9) after a drained heating-cooling cycle (20°C-70°C-20°C). This behavior agrees with the other studies in the literature Baldi, Hueckel, and Pellegrini 1988;Campanella and Mitchell 1968;Cekerevac, Laloui, and Vulliet 2005;Cui et al. 2011;Donna and Laloui 2015;Hueckel and Pellegrini 1992;Mitchell 1969;Plum and Esrig 1969). Such thermally induced volumetric strains alter the pore size distribution of the tested specimen (Darbari, Jaradat, and Abdelaziz 2017) and its particle orientations . ...
This article presents the development, calibration, and performance of a triaxial cell developed to study the thermomechanical behavior of soils under controlled heating and cooling rates and sinusoidal temperature changes mimicking real field conditions. This cell uses bipolar thermo-electrical devices to fully control the applied thermal loads. The cell can accommodate specimens up to 75 mm in diameter with a height-to-diameter ratio of 2 to 2.5. Tested soil specimens can be subjected to temperatures ranging from −5°C to 70°C with the specimen temperature change rate ranging from ±0.001°C/min and ±0.4°C/min. First, the modifications implemented on a conventional triaxial cell are presented to facilitate controlling of the boundary temperature applied to the specimen and the applied heating/cooling rates. Then, the thermal calibrations of the modified triaxial cell under different isotropic stresses and temperatures in drained and undrained conditions are presented. Finally, the capabilities of the modified triaxial cell are demonstrated using a thermomechanical test on a remolded kaolinite clay subjected to a drained heating-cooling cycle. The specimen was saturated and consolidated under 500 kPa confining stress at 20°C; then it was subjected to a drained thermal cycle (20 – 70 – 10 – 20°C) using a temperature change rate of ±0.1°C/min. Upon completing the thermal cycle, the specimen was sheared under undrained conditions at 20°C. The results of this test show a thermally induced contractive plastic volume change agreeing with the thermomechanical behavior of saturated normally consolidated clays in the literature. Furthermore, the drained heating-cooling cycle caused a dramatic increase in the undrained shear strength compared to the value measured at 20°C.
... Wood et al. (2009) 76 reported that the typical daily cycle of a heat pump consists During heating and cooling seasons, the temperature at 98 the soil-concrete interface varies between 1°C and 33°C, 99 respectively (Brandl, 2006;Hamada et al., 2007;Wood 100 et al., 2009;Abdelaziz et al., 2011;Shang et al., 2011;101 Rouissi et al., 2012;Akrouch et al., 2013), and could be 102 higher than 40°C for a cooling dominated environment 103 or when the energy piles function as solar energy storage 104 sinks (Gabrielsson et al., 2000). Around energy piles, the 105 temperature of the soil decreases with radial distance (Campanella and Mitchell, 1968;Demars and 119 Charles, 1982;Uchaipichat and Khalili, 2009;Tawati, 120 2010 Baldi, 1990;Cekerevac and Laloui, 2004). When subjected 129 to undrained heating, soils experience positive pore water 130 pressures due to differential thermal expansion between 131 water and soil particles (Cary, 1966;Tawati, 2010;Bai 132 et al., 2014). ...
... When subjected 129 to undrained heating, soils experience positive pore water 130 pressures due to differential thermal expansion between 131 water and soil particles (Cary, 1966;Tawati, 2010;Bai 132 et al., 2014). For unsaturated soils, Uchaipichat and 133 Khalili (2009) (Campanella and Mitchell, 1968;Eriksson, 139 1989;Graham et al., 2001;Saix et al., 2000;Uchaipichat 140 and Khalili, 2009), which is summarized by Alsherif and 141 McCartney (2016). However, an increase of the rate of sec-142 ondary consolidation due to heating was observed by Plum 143 and Esrig (1969) and Fox and Edil (1996). ...
... While cooling 144 has a slight effect on the rate of secondary consolidation 145 (Fox and Edil, 1996;Burghignoli et al., 2000). 146 Soils surrounding energy piles are subjected to tempera-147 ture cycles due to the intermittent operation (Fig. 1d); how-148 ever, the effects of temperature cycles on soil volume 149 changes have been investigated by few researchers (i.e. 150 Campanella and Mitchell, 1968;Demars and Charles, 151 1982;Burghignoli et al., 1992;Vega and McCartney, 152 2015; Lazenby et al., 2017;Xiao et al., 2017b). These 153 researchers concluded that when subjected to cyclic tem-154 perature change, soils experience an accumulated perma-155 nent volumetric contraction (Fig. 1d) regardless of stress 156 history (Alsherif and McCartney, 2016). ...
The intermittent operation of the ground source heat pump connected to thermo-active geo-structures (e.g. energy piles) results in cyclic thermal loading on the soil-structure interface. To investigate the effects of cyclic thermal loading on soil-structure interface properties, a conventional direct shear device was modified by replacing the bottom shear box with a concrete plate (with smooth and rough surfaces) that has embedded aluminum tubes to heat and cool the interface. A series of tests were performed with interface temperatures of 4.5, 22.5, and 42.5 °C, respectively. The constant normal stresses of the direct shear tests were 27.6, 41.4, and 100 kPa. The tests were conducted both under cooling and heating conditions with thermal cycle numbers of 0.5 and 10.5. The tests were conducted at a shearing rate of 3 mm/min. The effects of water content changes on the shear strength of soil-concrete interface was also investigated by performing tests with soil water content ranging from 15% to 19%. The responses of soil-concrete interface subjected to temperature change and cycles and different water contents are presented in this paper.
... After the realisation that soils in geotechnical engineering are not always restricted to isothermal conditions, intensive research on soils' thermomechanical properties has been conducted, after the pioneering work by Campanella & Mitchell (1968). In the past 30 years, a variety of temperature-controlled laboratory tests have been conducted on different soils to investigate their thermomechanical properties (Baldi et al., 1988;Hueckel & Baldi, 1990;Kuntiwattanakul et al., 1995;Tanaka et al., 1997;Sultan et al., 2002;Cekerevac & Laloui, 2004;Abuel-Naga et al., 2007). ...
... Based on the experimental observations, various constitutive models were proposed to interpret the thermally induced yield mechanism and reproduce the temperature-related stress-strain relationships of soils (e.g. Hueckel Campanella & Mitchell, 1968) 1990; Cui et al., 2000;Graham et al., 2001;Laloui & Cekerevac, 2003Cekerevac & Laloui, 2004;Abuel-Naga et al., 2007Tang et al., 2008;Hueckel et al., 2009;. For example, Hueckel & Borsetto (1990) proposed one of the first temperaturedependent critical state models, with the assumption that the stress rate excursions inside the current yield surface are admissible plastic processes when the temperature increases. ...
... In other words, the temperature-induced void ratio change of NC soils can be considered independent of stress levels. According to experimental observations (Campanella & Mitchell, 1968;Baldi et al., 1991;Towhata et al., 1993;Sultan et al., 2002;Cekerevac & Laloui, 2004), the following two simple equations are developed to describe the elastic and plastic strains due to both the temperature change and the stress change. ...
A constitutive, non-isothermal unified hardening (UH) model is presented to interpret the thermo-elasto-plastic behaviours of normally consolidated and overconsolidated clays. Two yield surfaces are adopted in the proposed model: the current yield surface and the reference yield surface. A UH parameter (H) is developed to describe the evolution of the current yield surface, and the plastic volumetric strain is employed to quantify the hardening of the reference yield surface. The similarity ratio (R T) between the current yield surface and the reference yield surface, which is a function of the temperature and the plastic volumetric strain, is developed to govern the volume change behaviour and the shear strength of soils with different stress histories and at varying temperatures. The performance of the proposed model is then discussed in five typical scenarios: isotropic heating and cooling, drained/undrained triaxial compression with constant temperatures, and heating under constant non-isotropic states (drained/undrained). The mechanisms for thermal contraction/swelling and thermal failure are interpreted within the framework of the proposed non-isothermal UH model. Finally, the proposed model is validated through test results in the literature: heating/cooling tests, temperature-controlled drained triaxial compressions, and temperature-controlled undrained triaxial compressions.
... The thermo-hydro-mechanical behavior of earth materials attracted research interests over the last few decades because of various practical temperature-dependent challenges in geo-engineering, including nuclear waste disposal (Kitagawa 1972;Borsetto et al. 1984;Hueckel, Borsetto, and Peano 1987;Gens et al. 2009), geothermal applications (Kavanaugh and Rafferty 1997;Rybach and Eugster n.d.;Fan et al. 2007;Abdelaziz, Olgun, and Martin 2015), and energy foundations (Olgun, Abdelaziz, and Martin 2013;Abdelaziz and Ozudogru 2016;Brandl 1998;Laloui et al. 1999;Knellwolf, Peron, and Laloui 2011;Amatya et al. 2012;Abdelaziz 2016;Jaradat and Abdelaziz 2018;Murphy and McCartney 2015;McCartney, Murphy, and Henry 2015;Chen and McCartney 2017;McCartney and Murphy 2017). Current experimental and numerical thermo-hydro-mechanical studies focused on understanding the macroscale behavior of soils subjected to various thermal and mechanical loads (Abuel-Naga, Bergado, and Bouazza 2007;Abuel-Naga, Bergado, and Lim 2007;Donna and Laloui 2015;Campanella and Mitchell 1968;Plum and Esrig 1969;Mitchell 1969;Baldi et al. 1985;Hueckel and Baldi 1990;Hueckel, François, and Laloui 2009) at different degrees of saturations (Alsherif and McCartney 2015;McCartney 2014a, 2014b;Vega and McCartney 2015). These studies successfully established our understandings regarding the macroscale thermo-hydro-mechanical behavior of soils; however, they do not provide a clear explanation about the underlying thermally induced microstructural changes that control the overall soil behavior (Lambe 1958;Mitchell and Soga 2005;Santamarina, Klein, and Fam 2001;Jaradat et al. 2017;Darbari, Jaradat, and Abdelaziz 2017). ...
... These studies successfully established our understandings regarding the macroscale thermo-hydro-mechanical behavior of soils; however, they do not provide a clear explanation about the underlying thermally induced microstructural changes that control the overall soil behavior (Lambe 1958;Mitchell and Soga 2005;Santamarina, Klein, and Fam 2001;Jaradat et al. 2017;Darbari, Jaradat, and Abdelaziz 2017). The absence of this microstructural explanation contributed to some misunderstood concepts for several years, such as the overlooked effect of the loading direction on thermally induced volume changes McCartney 2016a, 2016b) and thermal evolution of the compression and recompression indexes (Campanella and Mitchell 1968;Graham et al. 2001). ...
... Finally, and more critically, neglecting the confining pressure limited the applicability of the findings to practical conditions. This is because the current macroscale understandings of the thermomechanical soil microstructure evolution suggest that it depends on the applied confining pressure and stress history (Campanella and Mitchell 1968;Baldi, Hueckel, and Pellegrini 1988;Abuel-Naga, Bergado, and Lim 2007;Bergado, Abuel-Naga, and Bouazza 2006) and loading and unloading direction McCartney 2016a, 2016b). Moreover, neglecting the confining stress effect would most likely overestimate the changes in the soil microstructure, since the fabric is free to move. ...
This article presents a thermomechanical triaxial cell modified to fit inside a synchrotron X-ray diffraction (XRD) beamline aiming to assess thermally induced microstructural changes in saturated clays under in situ conditions. Understanding these thermally induced microstructural alternations in clays will explain some of the poorly understood or misunderstood concepts about the thermomechanical behavior of these soils; this, in turn, will allow more robust designs of geostructures for thermal and energy applications. Compared to other techniques, synchrotron diffraction provides (1) high accuracy and sensitivity to small changes compared to benchtop XRD and (2) the
ability to assess microstructure changes under in situ conditions (i.e., stress, saturation, and temperature). The design and selection of the various materials used in the modified triaxial cell are
first presented. Based on this design, it is recommended to use (1) sample diameters in the 5 to 7–mm range to minimize sample disturbance during trimming and X-ray background scattering
during X-ray scans and (2) a transparent cell with acrylic walls, with nitrogen gas as the confining fluid and neoprene membranes, since all considered cell wall materials (i.e., acrylic and aluminum), confining gases (i.e., nitrogen, carbon dioxide, argon, and compressed air), and membrane materials (i.e., latex and neoprene) result in accurate diffraction measurements. The modified cell was then used to assess the changes in particle reorientations of a normally consolidated kaolinite clay after the saturation and consolidation stages as well as the heating load. The results showed that the saturation and consolidation stages reoriented the particles perpendicular to the longitudinal axis of the sample, which is the same direction as the pore water flowing in and out of the sample. Further particle reorientations were observed due to heating.
... The smaller induced PWP rise in the first cycle (≈3.5 kPa) compared to that in the subsequent cycles (≈6.5-7 kPa) could be linked to the temperature-induced clay contraction (thermal consolidation) occurring during the heat cycles. In fact, the majority of thermal consolidation occurs in the first cycle, while it is expected to be smaller in the subsequent heat cycles, as shown by Campanella and Mitchell (1968) and Yazdani et al. (2018). This volumetric behavior of clay during thermal cycling is similar to its compression or swelling response to isotropic loading and unloading cycles (Campanella and Mitchell 1968). ...
... In fact, the majority of thermal consolidation occurs in the first cycle, while it is expected to be smaller in the subsequent heat cycles, as shown by Campanella and Mitchell (1968) and Yazdani et al. (2018). This volumetric behavior of clay during thermal cycling is similar to its compression or swelling response to isotropic loading and unloading cycles (Campanella and Mitchell 1968). Thus, a lower porosity and permeability condition is achieved by the clay at the end of the first cycle. ...
... It is generally known, however, that saturated NC clays show a contractive response during heating, which contrasts with the classical expansive behavior of other porous material subjected to heating. In fact, although both clay particles and pore water undergo thermal expansion, the excess PWP induced due to the discrepancy in their thermal expansion coefficients produces a reduction in porosity if drainage is allowed, thus causing a decrease in volume (Baldi et al. 1988;Campanella and Mitchell 1968;Burghignoli et al. 2000). In the present study, since drainage was permitted through some holes in the container's base, a contractive behavior was expected to occur. ...
Cyclic temperature changes in an energy pile generate cyclic thermal expansive/contractive strains along the interface, which may impact both the serviceability and the ultimate pile resistance. This paper aims to assess induced changes in the shaft resistance of an energy pile after being subjected to different temperature variation, between 24°C and 34°C. This was done by measuring the load-settlement curve of a laboratory scale floating energy pile installed in fully saturated NC kaolin. 10% relative settlement criterion was adopted to define the shaft resistance. Changes in temperature and pore pressure were also monitored in the surrounding clay using embedded thermocouples and a pore pressure transducer. Measurements during thermal loading showed that a positive excess pore water pressure was generated during the first thermal cycle followed by a negative pore pressure (suction) during the same cycle, while subsequent thermal cycles generated a cyclic pore pressure that remained negative regardless to the number of thermal loading cycles. It was also observed that piles subjected to heating exhibited greater shaft resistance than the reference pile tested at room temperature. Although the shaft resistance was considerably influenced by cyclic thermal loading, increasing the number of thermal cycles didn’t make appreciable differences in shaft resistance.
... The underlying mechanism of the thermal consolidation phenomena was explained by Campanella and Mitchell (1968) in their pioneering study, which suggested that the differential thermal expansion occurring due to the difference between the volumetric expansion coefficient of soil-solids, α s , and pore-water, α w , of the constituents of the soil mass, would lead to the development of excess pore-water pressure, Δu θ , which in turn is the primary cause of thermal consolidation. In addition, simultaneous decrease in viscosity, μ, of water observed at higher temperature and structural rearrangement of the soil grains under thermal stresses would also contribute to the variation in the rate and amount of thermal consolidation of the soil mass, respectively. ...
... where, η is the porosity, m v is the compressibility of the soil matrix and α sθ is a coefficient (refer Eq. 2) that defines structural rearrangement of the grains of the soil mass due to thermal stresses. In a way, α sθ is analogous to the secondary compression that is defined in the 'mechanical consolidation' of the soils (Campanella and Mitchell, 1968). ...
... Although, the primary cause of thermal consolidation phenomena remains the same irrespective of soil types and their stress-state, several influencing factors such as thermo-mechanical stress path, over-consolidation ratio, thermal stress history (i.e., number of thermal cycles) and degree of saturation of the fine-grained soils are known to affect their volume change characteristics, VCC. In this context, initial studies were conducted by employing conventional oedometer and maintaining the temperature of the water bath to establish the effect of elevated temperature on consolidation characteristics of the finegrained soils by Campanella and Mitchell (1968). These investigations revealed that the pre-consolidation pressure, σ p ′ , of the fine-grained soils decreases with an increase in temperature. ...
Know-how of volume change characteristics, VCC, of the fine-grained soils, exposed to thermal stresses, is essential for design of various thermo-active structures. These stresses are known to induce excess pore-water pressure, Δuθ, in the saturated state of such soils, which in turn affects their compression and shear strength characteristics. In this context, through several experimental studies, the effect of thermo-mechanical stress-path, the over-consolidation ratio (OCR) and degree of saturation on VCC (viz., thermally induced volumetric strain, ε_vθ, compression and re-compression indices, cc and cr) of the fine-grained soils has been demonstrated by earlier researchers. However, the response of these soils when exposed to sequential thermal and mechanical stresses, STMS, due to temperature fluctuation and continued infrastructure development, on VCC has seldom been studied. This motivated us to investigate the VCC of the fine-grained soils, by subjecting them to STMS in a suitably modified oedometer setup which facilitates temperature controlled tests. From the results of STMS tests, it is seen that the ε_vθ of these soils exposed to thermal cycles (20-60-20℃) is independent of the thermal stress history experienced at different applied vertical stress, σv, (= 60, 125, 250 kPa). Furthermore, from the analysis of deformation-time curve of the thermal loading phase, a methodology for direct determination of the volume change component of fine-grained soils, due to structural rearrangement, ΔVsθ, has been proposed. The methodology enables direct computation of the coefficient of volume change due to structural rearrangement, αsθ, that would aid in direct prediction of Δuθ from the deformation-time curve of thermal loading phase.
... And vice versa, cooling induces decrease in pore water pressure and increase in cohesion force. Studies of (Bai & Su, 2012;Burghignoli et al., 2000;Campanella & Mitchell, 1968;Fuentes et al., 2016;Hueckel & Pellegrini, 1992) on the effect of temperature change to the behavior of clay soil showed that, under undrained condition testing, heating increased the average pore water pressure of about 1÷3 kPa/°C. The pressure change of pore-water, according to these authors, is related not only to the difference of the expansion coefficient between the water and soil, but also depends on the volumetric stiffness of soil skeleton. ...
... The pressure change of pore-water, according to these authors, is related not only to the difference of the expansion coefficient between the water and soil, but also depends on the volumetric stiffness of soil skeleton. In addition, the study of Campanella and Mitchell (1968) pointed out that, the thermal cycles caused accumulation of excess pore water pressure. ...
... show that the behavior of sand-concrete interface is not affected by the temperature variations. However, the shear strength of clay-concrete interface increases with heating while the friction angle of the interface slightly reduces at high temperature. This phenomenon can be explained by the thermal consolidation observed during drained heating.Campanella & Mitchell (1968) has conducted experiments on clayed soil to investigate the behavior of soil under thermal cycles. Thermal cycles (temperature varying from 18 °C to 60 °C) were applied to the soil under constant stress conditions. The results show irreversible volumetric strain under this thermo-mechanical loading. After several thermal cycles, the med ...
The thermal and thermo-mechanical behavior of energy piles is investigated by various approaches: laboratory measurement on small soil samples, physical modeling on small-scale pile, experiments on real-scale pile, and analytical/numerical calculations. First, the thermal conductivity of unsaturated loess is measured simultaneously with moisture content and suction. The results show a unique relationship between thermal conductivity and moisture content during a wetting/drying cycle while a clear hysteresis loop can be observed on the relationship between thermal conductivity and suction. Second, thermal tests are performed on a full-scale experimental energy pile to observe heat transfer at the real scale. Third, an analytical solution is proposed to simulate conductive heat transfer from an energy pile to the surrounding soil during heating. The above-mentioned tasks related to the thermal behavior are then completed by studies on the thermo-mechanical behavior of energy piles. On one hand, experiments are performed on a small-scale pile installed either in dry sand or in saturated clay. Thirty thermal cycles, representing thirty annual cycles, are applied to the pile under various constant pile head loads. The results show irreversible pile head settlement with thermal cycles; the settlement is higher at higher pile head load. In addition, the irreversible thermal settlement is the most significant during the first cycles; it becomes negligible at high number of cycles. On the other hand, the experimental work with small-scale pile is completed with numerical calculations by using the finite element method. This approach is first validated with the results on small-scale pile prior to be used to predict the results of full-scale experiments
... The theoretical relationships between temperature increment and induced thermal volumetric change in a soil were proposed and explained by Campanella and Mitchell (1968), which is basically a "pore water volume"-based technique. Assuming fully saturated condition, the thermal volumetric changes of clay will occur through changes in the volume of solid particles and pore water. ...
... where V s and V w are solid particles and pore water volumes, respectively; α s and α w are the coefficients of thermal expansion of solid particles and pore water, respectively. The study by Campanella and Mitchell (1968) suggested using 3.5 × 10 −5 ð 1°C Þ for α s and 2.1 × 10 −4 ð 1°C Þ for α w . ...
... In drained thermal loading, the excess pore pressure induced by thermal expansion discrepancy between pore fluid and solid particles is allowed to be dissipated. This may possibly produce reduction in porosity as indicated in the literature (Baldi, Hueckel, and Pellegrini 1988;Campanella and Mitchell 1968;Burghignoli, Desideri, and Miliziano 2000). However, Darbari, Jaradat, and Abdelaziz (2017) have recently shown that thermally induced reduction in porosity should be interpreted in terms of the anisotropic thermal expansion coefficient of clay particles. ...
The soil response to daily temperature variation imposed by an energy pile is critical for estimating energy pile’s capacity and serviceability. It is, therefore, necessary to determine the temperature-induced effects on mechanical properties of soils. This paper presents the results of an experimental study on the effects of thermal loading on shear strength of reconstituted kaolin clay. The study was performed using a triaxial testing apparatus capable of applying thermal loading. Different cyclic and non-cyclic thermal loadings, with temperatures ranging between 24° C and 34°C, were applied. In addition, two theoretical mechanisms defining force distribution at inter-particle level were used to analyze the shearing behavior of clay under thermal loading. Both experimental and theoretical results indicate that the influence of temperature variation on the shear strength of clay is primarily controlled by stress state and stress history
... The thermal expansion coefficient of pore water is approximately seven to ten times that of most soil particles (Campanella and Mitchell, 1968). When the temperature increases, the thermal expansion of pore water may be limited by the soil skeleton, resulting in the generation of excess pore water pressure. ...
... The value of a s depends on the clay mineral, and a w is a constant. According to Campanella and Mitchell (1968) and Burghignoli et al. (2000), ...
In recent years, energy piles have been widely used in the collection of shallow geothermal energy. However, the engineering characteristics of the soil and the mechanical behavior of the pile are affected by temperature, especially in clay. To explore the influence of heating-cooling cycles on the thermo-mechanical response of an energy pile in saturated clay, a laboratory model test was designed. The energy pile in saturated clay was subjected to ten heating-cooling cycles. A fiber Bragg grating (FBG) system was adopted to monitor the pile strain. Meanwhile, pile and soil temperature, pore water pressure, and pile top displacement data were collected by a dynamic acquisition instrument. The results show that FBG sensors can achieve good results in measuring the axial strain of the pile. The distribution and transmission of thermally induced axial force and stress are affected by soil properties and pile constraints. Temperature cycling will lead to the thermal consolidation of saturated clay, improving the bearing performance of energy piles, and to an irreversible settlement of the energy pile.
... The three compression curves are approximately parallel, which means the time effect on clay can be considered independent of stress level. According to the experimental evidence in Fig. 3a, Bjerrum [6] proposed the time-line concept in which the compression curves corresponding to different creep times are called time-lines and are completely parallel, as shown as the three time-lines in On the other hand, Campanella and Mitchell [9] conducted one-dimensional compression tests under different temperatures. The obtained compression curves are illustrated in Fig. 4a. ...
... (b) j: Ericsson [14], Graham et al. [16] and Tanaka et al. [38] considered that j increases with the rising temperature. But Campanella and Mitchell [9], Crilly [12], Tsutsumi and Tanaka [44] and Yashima et al. [44] suggested that j is independent of temperature according to testing data. The authors of this paper would assume that j has a similar nature to that of k. ...
Clay is under the coupling influence of both time and temperature in some innovative geomechanical problems. Previous experimental researches have confirmed that time and temperature affect the overconsolidation degree of clay and induce overconsolidated characteristics. However, the experimental findings have not been included in constitutive models so far. This paper presents an innovative thermo-viscoplastic constitutive model based on the unified hardening model for overconsolidated clay. The new model combines the effect of time and temperature on overconsolidation by incorporating a temperature variable and a time variable into the hardening law and simultaneously considers the overconsolidated characteristics of clay by using the unified hardening parameter. The simulated results for laboratory tests show that the proposed model can not only reflect the influence of temperature and strain rate on the preconsolidation pressure, the undrained shear strength and the flow rule, but also describe the failure after undrained heating and creeping.
... Buisman (1936) fut l'un des premiers à montrer que, dans un essai oedométrique unidimensionnel, la compression secondaire dans les argiles suit approximativement une relation linéaire quand le tassement est tracé en fonction du logarithme de temps et ceci indépendamment de l'épaisseur de l'éprouvette ( Figure 1.5). Par la suite, beaucoup d'autres ont rapporté cette linéarité de la compression secondaire (Cox, 1936 ;Langer, 1936 ;Leonards et Altschaeffl, 1964 ;Barden, 1969 ;Mitchell et al. 1968 ;Mesri et al., 1973et Ladd et al., 1977, cependant, le coefficient de fluage est exprimé différemment selon les auteurs. ...
... légèrement l'indice de compression Cc et l'indice de gonflement Cg. Dans le cas d'une argile illitique remaniée,Campanella et Mitchell, (1968) ont indiqué que les variations de Cc et Cg avec la température étaient négligeables. Ce phénomène a été confirmé par la suite par de nombreux autres auteurs(Tidfors et Sallfors, 1989 ;Burghignoli et al., 2000 ;Cekerevac et al., 2002 ;Sultan et al., 2002 ; Cekerevac et Laloui, 2004). ...
Les argiles compactées sont utilisées dans de nombreuses applications, notamment en géotechnique et en géotechnique de l’environnement, en raison de leur faible perméabilité, et de leurs propriétés de rétention notamment. Cependant, une fois en place, ces matériaux pourraient être exposés à des sollicitations thermiques et/ou hydriques, à long et très long terme. L’objectif principal de ce travail est de quantifier expérimentalement l’impact de ces sollicitations sur la compressibilité d’une argile compactée, et plus particulièrement son fluage. Avec cet objectif, des cellules œdométriques à température contrôlée entre 5 et 70°C ont été développées. Deux types d’œdomètre à succion contrôlée par les méthodes osmotique et solutions salines ont été employés dans une gamme de succion comprise entre 0 et 20,8 MPa, et à une température constante de 20°C. Ces dispositifs ont permis d’étudier le fluage jusqu’à une contrainte verticale de 3600 kPa. L’étude s’est concentrée sur le comportement d’une argile moyennement gonflante compactée. Les résultats obtenus ont tout d’abord montré que la contrainte de préconsolidation apparente σ’p diminue à mesure que la température augmente. Le coefficient de fluage Cαe augmente avec la température, cet effet étant plus particulièrement marqué à des contraintes plus élevées. Une relation linéaire entre le coefficient de fluage Cαe et l’indice de compression incrémental C*c a été observée dans la plage de contraintes considérée et le rapport (Cαe /C*c) dépend de la température. Ensuite, deux approches expérimentales complémentaires (essais de fluage par paliers ou à vitesse de déformation contrôlée) ont mis en évidence la dépendance des caractéristiques de fluage vis-à-vis de la succion du sol. Par ailleurs, la contrainte de préconsolidation apparente σ’p augmente avec l’augmentation de la vitesse de déformation έv et de la succion. En revanche, l’indice de compression Cc et le coefficient de fluage Cαe varient d’une manière non monotone avec une valeur maximale sous une succion de 3,5 et de 2 MPa, respectivement. L’évolution de ces paramètres apparaît fortement liée à la structure interne du sol. L’analyse de la variation de σ’p avec έv et de Cαe avec Cc a montré que la relation Δlog σ’p /Δlog έv = Cαe/Cc est également valable pour le sol argileux compacté étudié dans les cas saturés et non saturés
... Set EP-F as an example, after five thermal cycles, positive thermally induced pore water pressure equal to 186% of the u 0 was accumulated for HO, while negative pore water pressure of -199% of the u 0 was accumulated for CO. This phenomenon could also be explained by the accumulated soil temperature that the thermally induced pore water pressure could be triggered by the increase or decrease in soil temperature [6]. ...
... Change in additional tip resistance: a RP-E in reference test; b EP-E change with temperature in HCO; c EP-E change with temperature in HO induced by the difference in the thermal expansion coefficient of water and the soil solids[6]. ...
The thermal–mechanical behavior of the energy pile under three kinds of climatic conditions was investigated in this study. A small-scale floating energy pile and a small-scale end-bearing energy pile, which were embedded in normally consolidated clay, were employed. The energy piles were subjected to cyclic heating/cooling, heating/recovery and cooling/recovery to simulate the energy pile work in the regions of warm/cold balanced climate, warm-dominated climate and cold-dominated climate, respectively. The thermal response and the mechanical response of the energy pile under different climatic conditions, as well as the different response between the floating energy pile and the end-bearing energy pile, were analyzed and discussed comprehensively. The results show that the thermo-mechanical performance of energy pile depends on the types of climatic conditions, and the behavior of the floating energy pile is different from the end-bearing pile. Larger irreversible displacement could be induced by thermal cycles for the floating energy pile compared to the end-bearing energy pile, while irreversible tip resistance could be induced for end-bearing energy pile. Under warm/cold balanced climate, the largest irreversible tip resistance and pile displacement could be induced for end-bearing energy pile and floating energy pile, respectively, and the smallest thermally induced irreversible displacement was observed when the energy pile was under cold-dominated climate.
... As the temperature rises, the permafrost and seasonal 2 permafrost thaw slowly, and the temperature and unfrozen water content change correspondingly, which greatly affects the mechanical properties and hydrological characteristics of the soil. Permafrost is a complex porous medium composed of solid particles, liquid water, gas and ice, and the content of various components is an essential index for thermal calculation of permafrost, so it is particularly necessary to study the distribution curve of pore radius from the microscopic pore structure level [1][2][3][4]. ...
... According to Habibagahi (1973) and Delage et al. (2000), temperature increase reduces the viscosity of pore water, which leads to greater hydraulic conductivity in clay. An increase of temperature also expands the volume of the pore water and generates pore water pressure inside clay under undrained conditions (Campanella and Mitchell, 1968;Demars and Charles, 1981;Abuel-Naga et al., 2007). In terms of consolidation rate, this earlier research implied that the injection of heat into clay can accelerate the consolidation process. ...
Temperature change affects the consolidation behavior of soft clay. An increase in temperature in soft clay leads to the dissipation of excess pore water pressure and the decrease of volume. This temperature-induced consolidation can be utilized as a novel approach to improve soft ground. In this study, in order to investigate the effect of heat injection through a vertical drain on soft ground consolidation, a test device was designed to install different-sized sand drains that enabled heat injection and temperature control of a vertical drain. Using the device, a series of consolidation tests was performed with varying heat injection and varying diameter of the vertical drain. During consolidation, vertical settlement and temperature at various locations in the ground were measured. After each consolidation test, the spatial distribution of void ratio in the ground was estimated. Test results showed that heat injection increased the radial temperature of the ground, and the increasing diameter of sand drain with an internal heat source also expanded the heating area in the ground. Furthermore, the larger diameter sand drain led to greater final settlement and lower void ratio.
... Dans le cas de la consolidation mécanique, les études se sont attachées à caractériser les évolutions des indices de compression élastique et plastique ainsi que de la contrainte de préconsolidation du sol. Campanella & Mitchell (1968), Eriksson (1989), Tidförs & Sällfors (1989), Lingnau et al. (1995) et Belanteur et al. (1997 montrent que les indices de compression élastique et plastique sont peu sensibles à la température. En conditions oedométriques (Eriksson (1989) et Tidförs & Sällfors (1989)) ou triaxiales (Hueckel & Baldi (1990), Tanaka et al. (1997), Cui et al. (2000), Graham et al. (2001), Sultan et al. (2002) et Ghembaza et al. (2014)), les résultats obtenus sur différents sols de nature argileuse montrent une diminution de la contrainte de préconsolidation lorsque la température augmente. ...
The research work presented in this scientific report was carried out within the "Innovative Structures, Geomaterials, EcoCOnstruction" team of the Mechanics and Civil Engineering Laboratory of the University of Montpellier. They are part of the research axis "Geomaterials" on the experimental study of the thermo-chemo-hydro-mechanical behavior of geomaterials.
Experimentation on geomaterials is a necessity if one wishes to observe the pathologies of structures in order to understand the mechanisms, often multi-physical, governing their appearance. This scientific aspect requires, for those who undertake it, qualities such as rigor, patience and perseverance, but also inventiveness in order to design, realize and develop precise experimental devices at different scales of observation. If in certain cases, "traditional" experimental devices may suffice for the desired investigations, the development of new experimental tools, often specific, is permanently associated with the mission of the experimenter to explore new horizons and project himself towards new perspectives in the understanding and experimental characterization of phenomena.
The geomaterials studied in the framework of this research are soils and cementitious materials which are multiphase granular materials formed of solid grains of various sizes, shapes and nature, and comprising a poral space filled with fluids with diverse physico-chemical properties. These multiphase media are most often subjected to multiple external stresses (mechanical, hydraulic or hydric, thermal, chemical, etc.) with more or less strong couplings leading inevitably to deformations related to rearrangements of solid grains or their deformations. One of the challenges for the experimenter is to be able to observe each phenomenon and to understand its action within geomaterials in order to predict the behaviour of structures, especially when it becomes critical with regard to stability, and therefore safety.
In the case of soils, instabilities are often linked to variations in water content that modify the internal stresses that can lead to shrinkage or swelling mechanisms, settlement and even, in extreme cases, collapse. Shrinkage or swelling phenomena, observable during drying or water soaking, are linked to the clayey nature of soils, whose behaviour depends on the initial state (initial dry density and moisture content) as well as on the external mechanical stresses applied to the soil. The settling phenomenon is due to variations in the mechanical stresses in the soils which generate more or less important granular rearrangements preceding the movement of water within the pore space. The collapse phenomenon can occur with or without the application of external mechanical stresses as soon as the soils show a generalized loss of local cohesion between the solid particles that ensured the stability of the whole. These phenomena can be more or less amplified if thermal conditions also vary.
In the case of cementitious materials, ageing may be accompanied by degradation which depends strongly on external conditions, but also on the chemical composition of the aggregates and cement paste. If, during hydration, an improvement in mechanical properties is observed, the structures in service are subject to external or internal actions depending on their conditions of use or execution, which may cause or promote irreversible degradation. These actions may be of thermal or chemical origin leading to the dissolution of cement compounds or the expansion of hydrates modifying internal stresses. Among the origins of degradation are high temperatures, leaching or internal sulfatic reaction. The rise in temperature induces hydric imbalances responsible for the increase in pressure of fluids in the pores but also generates mechanical imbalances related to the differential expansion between the aggregates and the cement paste causing cracking at the cement paste / aggregate interfaces. Leaching causes leaching of the hydrates of the cement paste which results in a loss of the mechanical properties of the cement but also and especially of the cement paste / aggregate interfaces. The internal sulfatic reaction corresponds to the delayed formation of ettringite which, through its expansion in the pores, modifies the internal stresses, especially at the cement paste/aggregate interfaces where the porosity is most often high.
In this context, my research work aims at contributing to the characterization of the mechanical properties and behavior of geomaterials by bringing my skills for the development and use of experimental techniques to highlight the different mechanisms leading to certain pathologies of structures. One of the originalities of the general experimental methodology is to associate local measurements at the scale of grains and interfaces, to macroscopic measurements at the scale of a representative elementary volume, through mesoscopic measurements at the scale of a few grains. The local scale is interested in the interactions between one or several grains connected by liquid or solid bridges, their characterization and their experimental modeling. The mesoscopic scale makes it possible to verify the relevance of the numerical tools developed internally at the LMGC, to ensure the transition of scales, on an experimental situation well mastered in terms of formulation and microstructure. Measurements at the macroscopic scale allow to validate the prediction tools developed on a sufficiently large volume for its behavior to be representative of an equivalent global behavior.
... When thermal energy is stored in clays, the material behaviour will change as a result of changing temperature. Early studies [88][89][90][91] and recent ones 59,92,93 have documented that the compression index was found independent of temperature, yet the higher the temperature, the lower the void ratio at any given consolidation pressure: ...
This paper presents a simple hypoplastic model capturing mostly all salient features of clays: rate dependency, time dependency and inherent and induced anisotropy without being restricted to only viscoplastic clays. Therefore, due to the strain rate decomposition into three parts, nonviscous clays, that is, rate‐independent clays, can also be simulated. The incorporation of a loading surface allows to capture the behaviour of normal and overconsolidated clays. The model requires eight material parameters, which are simple to calibrate from standard laboratory tests. In total, 77 simulations of five different clayey‐like soils are compared with experimental data. The simulations contain one oedometer test with loading–unloading–reloading cycles, creep and relaxation stages, both undrained and drained triaxial tests in compression and extension, as well as eight incremental response envelopes capturing also the directional response of Beaucaire Marl clay. Some limitations of the model such as the description of temperature effects on the behaviour of clays are also pointed out.
... In particular, the ice-water phase transformation caused by freezing-thawing cycles weakens bonding between soil particles and leads to fragmentation of loess aggregates (Li et al., 2018a). The temperature cycles may cause volumetric change (expansion or contraction) of soil particles, and therefore changes the structure of loess (Campanella and Mitchell, 1968). The dissolution of soluble salt may lead to disintegration of loess (Zhang et al., 2013(Zhang et al., , 2014. ...
Present-day loess, especially Malan loess formed in Later Quaternary, has a characteristic structure composed of vertically aligned strong units and weak segments. Hypotheses describing how this structure forms inside original loess deposits commonly relate it to wetting-drying process. We tested this causal relationship by conducting unique experiments on synthetic samples of initial loess deposits fabricated by free-fall of loess particles. These samples were subjected to a wetting-drying cycle, and their structural evolutions were documented by close-up photography and CT scanning. Analysis of these records revealed three key stages of structural evolution: initiation (evenly distributed cracks appear due to wetting); inhomogeneitization (some cracks grow, forming large polygons); and development (polygon-forming cracks grow further - cracks within polygons narrow down or heal up). These experiments successfully reproduced the characteristic structure of present-day loess, and led to a discovery that it is the wetting of initial loess that initiates and drives the structural evolution, while drying preserves and expands resulting features.
... Many studies have been carried out in order to investigate the effects of temperature on the mechanical behavior of soils. By the late 1960s the first thermo-mechanical model was proposed [3]. Although strains are consisted of elastic and inelastic responses, early models were able just to reproduce the elastic strains until the late 1980s that some models including plastic strain calculations were proposed [4][5][6][7]. ...
In the present study, the behavior of saturated clays while they are mechanically loaded under constant temperatures has been investigated by simulating thermal triaxial test. A critical state-based thermo-mechanical constitutive model has been added to the ABAQUS finite element (FE) software through a user subroutine to define the stress–strain, volume change and pore pressure behavior of saturated clays. In order to have better predictions by the numerical implemented model, it has been changed by defining a new plastic potential function similar to its yield surface. The model has been integrated via an explicit integration scheme. Verification of the discretized axisymmetric numerical model has been carried out by three different series of triaxial tests for both drained and undrained conditions, and the experimental results were compared with numerical simulations. According to these comparisons, the adopted numerical model is able to predict the results of thermal triaxial tests on saturated normally consolidated and overconsolidated clays in a good manner. The presented methodology is general and can be used for application of any other critical state-based thermal constitutive model in a FE program. Based on the results, it can be suggested to be implemented in similar thermal boundary value problems of geotechnical engineering.
... This may lead to additional lateral displacements in thermally-active MSE walls, which can be referred to as thermal softening (Stewart et al. 2014a). Although it is well accepted that temperature does not affect the compression indices and critical state friction angle of soils (Campanella and Mitchell 1968;Laloui et al. 2014), elevated temperatures may also lead to volumetric contraction in unsaturated soils McCartney 2016a, 2016b) and a thermal softening effect leading to a reduction in the peak shear strength and stiffness (Uchaipichat and Khalili 2009). The interaction between the effects of heat transfer and water flow on the effective stress state in unsaturated soils and the thermal softening of the geosynthetic reinforcements and soil must be carefully considered. ...
This study investigates the thermal soil-geosynthetic interaction mechanisms of reinforcing geotextiles confined in compacted silt that may be encountered when using mechanically-stabilized earth (MSE) walls as geothermal heat sinks. A thermo-mechanical geosynthetic pullout device was used that incorporates standard components for geosynthetic pullout or creep testing but also heating elements at the top and bottom of the soil box to apply boundary temperatures and dielectric sensors embedded in the soil layer to monitor distributions in temperature and volumetric water content. Two test series were performed: the first involves monotonic pullout of woven polypropylene geotextiles after reaching steady-state conditions under different boundary temperatures without a seating load, and the second involves monotonic pullout of woven polyethylene-terephthalate geotextiles after reaching steady-state conditions under different boundary temperatures with a seating pullout load. The results indicate that the pullout resistance of both geotextiles decreased with increasing temperature. Although heating led to drying of the unsaturated silt layers as expected, measurements from the second test series indicate accumulation of water at the silt-geotextile interface. An effective stress analysis considering thermal softening of soils indicates that the increase in effective saturation at the silt-geotextile interface was the cause of the decrease in pullout resistance with heating.
... Over the decades, extensive studies have been carried out to independently investigate the strain rate effect [4,17,19,25,29,42,44,53,57,62] and temperature effect [1,7,8,12,17,22,34,43,47,51,59] on mechanical behaviour of soft clay and temperature effect on sand [31,32,61]. On the other hand, limited studies were carried out to understand the combined effects of strain rate and temperature, with particular emphasis focusing on the onedimensional compression behaviour on soft clay [28,30,33,41,52]. ...
Marine clay supporting high-temperature offshore structure susceptible to random movements (such as a buckling high-temperature pipeline) experiences variable shearing rates at an elevated temperature that is higher than the marine environment (typically 4 °C). This practically implies that the undrained shear strength (su) of the marine clay being routinely characterized in situ by penetrometers at a constant rate under an isothermal condition (4 °C) should be carefully corrected, by taking into account the temperature and rate dependency. To date, the combined effects of rate and temperature on the undrained shear behaviour of marine clay are merely investigated experimentally and theoretically. This study presents the development of an anisotropic thermo-elastic–viscoplastic model and a series of temperature- and rate-controlled triaxial tests for validation purpose. Compared to the modified Cam-Clay model, the proposed model only introduces three new parameters to characterize the temperature dependency, rate dependency and the inherent anisotropy of K0-consolidated marine clay. The predictive capability of the model has been validated by the triaxial test results. Based on the new model, an explicit equation is formulated for quantifying the temperature- and rate-dependent su of marine clay. Calculation charts are also developed to quantify su of marine clay with different plasticity indexes under various strain rates and temperatures.
... The temperature rise causes a volume change of all the constituents of geomaterials (i.e., solid minerals, adsorbed and free waters, entrapped gases) according to their thermal expansion coefficient. Pore pressure is also generated upon undrained heating because of the difference between the coefficients of thermal expansion of solid skeleton and water(Campanella and Mitchell 1968, Abuel-Naga et al. 2007).Sygała et al. (2013)summarized the effects of high temperature on rock behavior and noted that the difference in thermal expansion of minerals leads to structural changes causing the change in strength parameters, bulk density, structural deformation, and wave propagation 102 velocity. Temperature rise also affects the yielding behavior (Hueckel and Baldi 1990) and range of elasticity (Hueckel and Borsetto 1990). ...
The design of underground critical facilities for anticipated effects of nuclear-air-blast is becoming a challenge. Moving air-shock waves on the earth surface generated due to above-ground nuclear-explosions induce ground displacements. An accurate estimate of nuclear-air-blast-induced free-field ground displacement is crucial for the design of such protective structures. This thesis provides a computationally efficient and reliable estimate of ground displacements considering nuclear-air-overpressure, stress-strain characteristics of geomaterials, and associated uncertainties.
Of several blast load models available in literature, the ASCE manual No.-42 model captures the mean trend of the decay portion of the air-overpressure time-history reasonably well. This model predicts nuclear-air-overpressure time-history in terms of distance from ground-zero (R), height-of-burst (HOB), and yield of the explosion (W). The ASCE model is further modified to account for the uncertainties associated with (i) the ASCE model, (ii) occurrence of an explosion, and (iii) inherent variability of nuclear-attack parameters (R, W, and HOB) by (i) comparing the field data with model estimates, (ii) developing a probabilistic threat scenario model, and (iii) assigning appropriate probability distributions to the nuclear-attack parameters, respectively. The incorporation of these uncertainties into the ASCE model leads to the probabilistic characterization of nuclear-blast loads. For the direct use in design, two simple correlations are proposed for peak overpressure and positive phase duration in terms of their respective probability of exceedance along with another equation that represents a normalized air-overpressure time-history.
An appropriate description of stress-strain relationship of geomaterials subjected to blast loading is the next important step. Previous experimental and theoretical research efforts indicated that the constitutive behaviour of geomaterials under blast loading depends upon strain rate, stress level, and interaction among the three phases (solid, liquid, and gases) and various advanced constitutive models are available to model such a stress-strain behavior of geomaterials. However, these models are based on large number of material parameters which needs to be calibrated through different experimental studies and numerical computations. Furthermore, the inherent variability of geomaterials, uncertainties of the nuclear-air-blast overpressures, epistemic uncertainties of the constitutive model itself would add significantly to the cost of computation of ground displacements. Therefore, as an alternative to advanced constitutive models, new functional forms, based on three parameters, namely, weight factor, initial modulus ratio, and strain recovery ratio, are proposed to capture the loading and unloading branches of experimentally determined or numerically simulated stress-strain curve of geomaterials subjected to blast loads. The three parameters are determined for an exhaustive data set of experimental stress-strain curves of different types of geomaterials (sands, silts, and clays) under different types of conditions (dry, saturated, partially saturated, confined, and unconfined) subjected to various loads (dynamic loads, blast loads, impact loads, and static loads) and a catalogue of the parameters is prepared for direct use by practitioners. It is observed that the functional forms reasonably capture the mean trend of the stress-strain data corresponding to not only blast loads and high strain rates but also to static and dynamic loads. The functions were also able to capture the stress-strain behaviour simulated from advanced constitutive models. The dependence of model parameters on strain-rate, lateral confinement, degree of saturation, initial compaction, and locking-initiation stress is also analyzed and some simple models or thumb-rules are proposed for reasonable estimation of the three parameters.
In the last step, to estimate the nuclear-air-blast-induced free-field vertical ground displacement a model is proposed in terms of air-overpressure time-history and depth-dependent geotechnical parameters (stress wave velocity, stress attenuation, and stress-strain model). The estimated displacement time-histories are compared with the nuclear as well as non-nuclear test data and a reasonable agreement is found between the recorded and estimated displacements. It is observed that the model significantly overestimates the displacements at greater depths and at larger distances from ground-zero (GZ). The displacement model is utilized further to study the effect of loading and geotechnical parameters on peak ground displacement through parametric variations and sensitivity analysis. The analysis indicates that the peak ground displacement is highly sensitive to R, HOB, and constrained modulus.
The field data is utilized further to characterize the epistemic uncertainties associated with the displacement model. Since the quantification of model uncertainties is computationally tedious if model parameters are also uncertain, an approximate approach is proposed for model uncertainty characterization that is based on Taylor’s series approximation and accounts for deterministic as well as uncertain input parameters. The proposed approach is compared with the computationally rigorous Bayesian approach and is observed to be in close agreement for prediction of mean model factors. Based on the proposed model uncertainty characterization approach, it is found that the mean model uncertainty factor (corresponding to peak displacement) varies between 0.78 and 0.99 for coefficients of variation of input parameters in the range of 0-20%. Since all the mean model uncertainty factors are less than unity, it indicates that the proposed model provides, on an average, conservative estimate of peak ground displacement.
Thus, using the proposed (i) probabilistic nuclear-blast load model, (ii) stress-strain function of geomaterials, (iii) displacement model, and (iv) model uncertainty factors, a reliable and computationally efficient estimate of nuclear-air-blast-induced ground displacements can be arrived at.
... Firstly, Campanella and Mitchell (1968) conducted a series of triaxial compression tests on clays at different temperatures and observed that, in undrained conditions, a rise in temperature (up to about 60°C) results in a pore pressure increase. They described the pore pressure change as being directly proportional to the expansion of the pore water due to the effect of temperature. ...
In landfills, due to their low hydraulic conductivity, compacted clays (CC) are commonly used in multilayered structures as base liners and cover systems. Nevertheless, the hydraulic performances of the CC layer can be affected by temperature alterations. The CC barrier of cover systems is exposed to heating caused by waste degradation processes as well as by the air temperature fluctuations, including freezing and thawing and high temperatures. Exposition occurs especially during transitory configurations when the final cap is not completed with the protective soil layers. In the present work, four clayey soils of varying plasticity all suitable for landfill barriers according to the international standard requirements are tested with respect to their sensitivity to thermal stresses in terms of hydraulic conductivity changes. For each material, experimental tests are performed on compacted specimens comparing the values obtained soon after compaction with the ones obtained after exposition to freezing-thawing or drying processes, the latter caused by heating up to 60 °C. The results show that freezing-thawing is more detrimental than heating, since the first can increase the hydraulic conductivity by up to about 20 times, while the second by less than 10 times. The soils of medium plasticity are the most affected, while the ones with high plasticity show the ability to partially withstand the effects of the investigated thermal alterations. This behavior seems related to the water absorption capacity of the material. The results suggest that the optimum water content acquired from the Proctor Standard curve seems to be a suitable indicator of this partial recovery potential.
... The temperature effect in the saturated zone (i.e. matric suction less than air entry suction) is consistent with the results reported by Campanella and Mitchell (1968). ...
Key engineering properties of unsaturated soils such as volume change and shear strength can be defined using the effective stress principle. Several problems like prolonged drought, high-level radioactive waste, buried high voltage cables can subject surface and near-surface unsaturated soils to elevated temperatures. Such elevated temperatures can affect the hydraulic and mechanical behavior of unsaturated soils. It is very important to develop a closed-form model that can reasonably estimate the effective stresses under different elevated temperatures. For this purpose, the current study incorporates the temperature effect into a suction stress-based representation of Bishop's effective stress. The proposed model accounts for the effect of temperature on matric suction and degree of saturation. A temperature-dependent soil water retention curve is used to account for thermal effects on surface tension, contact angle, and enthalpy of immersion per unit area. The proposed effective stress model is then used to calculate the effective stress for two soils, Pachapa loam, and Seochang sandy clay, at various temperatures ranging from 25°C to 100°C. The validity of the model is examined by comparing the predicted effective degree of saturation and suction stress values against the measured data reported in the literature for GMZ01 bentonite. At a constant net normal stress, the results for both soils show that the impact of temperature on effective stress can be significant. The proposed model can be used for studying geotechnical and geoenvironmental engineering applications that involve elevated temperatures.
... Several experimental and numerical research have been carried out to analyze the effects of thermal loading on hydraulic and mechanical properties of the porous media (e.g., soil) in transient and steady state conditions [17][18][19][20][21][22][23][24]. In the past two decades, thermo-poro-mechanical theory has been used to accurately predict the thermo-hydro-mechanical (THM) behavior of normally-consolidated and over-consolidated clays [20,25,26]. Thermo-elastoplastic constitutive models such as TEAM [27] and ACMEG-T [28] have been found to be useful in justifying the thermo-mechanical experimental studies on clays with different over-consolidation ratios. ...
... After reaching the residual saturation, applying higher temperature increases absolute magnitude of suction stress at a given matric suction. The temperature effect in the saturated zone is consistent with the results reported by Campanella and Mitchell (1968) and Tanaka (1995). Unlike for Shonai dune sand, the suction stress versus matric suction at each temperature shows a monotonic trend for Pachapa loam [ Fig. 3 ...
Effective stress is a critical factor controlling the mechanical behavior of unsaturated soils. There has been an increasing interest toward fundamental and applied research on emerging applications that involve unsaturated soils subjected to elevated temperatures. However, major gaps remain in the development of a unified model that can properly represent temperature dependency of effective stress in unsaturated soils. The main objective of this study is to develop closed-form equations to describe the effective stress of unsaturated soils under nonisothermal conditions. For this purpose, suction stress-based formulations are developed for representing temperature-dependent suction stress and effective stress of unsaturated soils. The formulations incorporate temperature-dependent moist air pressure and matric suction into a skeleton stress equation originally developed using volume averaging. A nonisothermal soil water retention curve (SWRC) is used to account for thermal effects on the adsorbed water, surface tension, contact angle, and enthalpy of immersion per unit area. The validity of the model is examined by comparing predicted suction stress values against experimental data reported in the literature for various soils ranging from clay to sand. The effective stress equations developed in this study can provide further insight into the behavior of unsaturated soils under nonisothermal conditions. The models can be readily incorporated in numerical and analytical methods, leading to more accurate modeling of unsaturated soils subjected to nonisothermal loading conditions.
... The role of temperature on the engineering properties of soil has been studied extensively (e.g. Campanella & Mitchell, 1968;Hueckel & Baldi, 1990;Delage et al., 2000;Cekerevac & Laloui, 2004;Gens, 2010;Ng & Zhou, 2014;McCartney et al., 2019;Vahedifard et al., 2019). More recently, micro-level techniques have been increasingly employed as an efficient means to provide further insight into the behaviour of soil (e.g. ...
The main objective of this study is to use a suite of micro-scale tests to characterise the temperature effects on high plasticity clay. The unheated clay was examined using X-ray diffraction, field emission
scanning electron microscopy (FESEM) and energy-dispersive X-ray spectrometry to characterise the mineralogy, morphology and the elemental composition of natural soil. The clay was then cured under
various temperatures ranging from 23 to 1000°C. The characteristics of heated clay were then evaluated using FESEM, cation-exchange capacity (CEC) tests, thermal gravimetric analysis (TGA) and
Brunauer–Emmett–Teller (BET) surface area analyser. The results show minimal changes in soil fabric with increased temperature. However, specific surface area and CEC are shown to significantly
decrease with temperatures beyond 100°C. TGA results can provide an insight into the drops of BET surface area and CEC. Depending on the range of temperature applied, the changes can be attributed
to the temperature effects on the clay microstructure, loss of capillary and adsorbed water and organic matter, and the clay mineral’s interaction with the displacement cation or nitrogen. The observed
trends are used to discuss possible implications on the hydro-mechanical properties of soil such as the soil–water-retention curve, shear strength and volume change.
... Paswell (Paaswell 1967) conducted heating test at constant load using odometer ring in 1967 and the first conference with focus on temperature related issues in soils was held in Washington DC, USA in 1969. The early studies of other researchers can be found in literature (Baldi, Hueckel, and Pellegrini 1988;Campanella and Mitchell 1968;Habibagahi 1977;Plum and Esrig 1969;Towhata, I., Kuntiwattanaku, P., Seko, I., & Ohishi 1993). The range of temperature was being investigated back then during early studies was restricted (usually between 10 to 50 °C). ...
In recent years, pollution and Global warming related issues and the proven effect of fossil energy on that have lead the attention toward finding a renewable and sustainable source of energy such as Geothermal Energy. An important challenge is to determine the maximum thermal energy accurately that the geothermal system can provide. Lack of suitable information might lead to malfunction and non-economical design. Ground temperature changes are dependent on the physical and thermal properties of the local geology at the site among which the thermal conductivity is the most important. The aim of this paper is to make a detailed review and summarization about the soil thermal properties and ground temperature profile. This information is of high importance and can help us to make sure about the quality and safety of designing the structures dealing with temperature change.
... Paswell (Paaswell, 1967) conducted heating test at constant load using odometer ring in 1967 and the first conference with focus on temperature related issues in soils was held in Washington DC, USA in 1969. The early studies of other researchers can be found in literature (Burghignoli et al., 2000;Campanella & Mitchell, 1968;Cekerevac, 2003;Hueckel & Baldi, 1990). The range of temperature was being investigated back then during early studies was restricted (usually between 10 to 50 °C). ...
In recent years, pollution and Global warming related issues and the proven effect of fossil energy on that have lead the attention toward finding a renewable and sustainable source of energy such as Geothermal Energy. Ground-source heat pump (GSHP) is a well-known type of geothermal structures commonly used for space heating and cooling. The water is circulated by ground heat exchanger (GHE) through the ground. Energy piles are now popular because of their ability to satisfy both energy and structure requirement. Circulation of fluid through the foundation will cause the temperature fluctuation on pile-soil interface, pile and the surrounding soil. It is known that this temperature fluctuation might have some effects on the pile-soil interface behavior. Suitable information on such behavior is of high importance and can help us to have a safe and efficient design of energy piles.
... To design for the serviceability of civil engineering structures supported by loess, it is essential to investigate the wetting collapse of loess at various temperatures. The thermal effects on soil behaviour are well recognized and modelled (Campanella and Mitchell 1968;Abuel-Naga et al. 2007;Uchaipichat and Khalili 2009;Yao and Zhou 2013;Zhou et al. 2015a;Ng et al. 2016a). For example, Yao and Zhou (2013) proposed an advanced constitutive model to consider the thermal effect, which is capable of describing the hardeningsoftening behaviour of soil with positive-negative dilatancy in nonisothermal conditions, based on a very powerful unified hardening equation (Yao et al. 2009). ...
Yielding and wetting-induced collapse are two important interrelated aspects of unsaturated loess behaviour. Previous studies on loess were generally conducted under a single temperature condition. The principal objective of this study is to investigate thermal effects on yielding and wetting-induced collapse of recompacted and intact loess. Isotropic compression tests were carried out to determine yield stress at different suctions (0 and 100 kPa) and temperatures (5, 23, and 50 °C). Moreover, wetting tests were conducted at various temperatures and stresses. Results of the wetting tests were interpreted using the measured yield stress at various suctions and temperatures. It is found that yield stress decreases with decreasing suction (wetting-induced softening). The wetting-induced softening of recompacted loess is more significant at a higher temperature. The observed thermal effects on wetting-induced softening are likely because with decreasing suction, the stabilizing interpar-ticle normal force decreases more at a higher temperature. In contrast, when the applied stress reaches the yield stress during wetting, yielding and plastic volumetric contraction can be observed. More importantly, wetting-induced contraction of recompacted loess at 50 °C is about three times of that at 5 °C. The larger contraction at 50 °C is mainly because the wetting-induced softening is larger at a higher temperature.
... François and Laloui (2008) summarize the primary interactions (labeled as 1 through 4 in Figure 1) between thermal, mechanical and hydraulic processes. For the interaction between thermal and mechanical processes, temperature change will result in soil expansion or contraction and depends on the soil type, initial relative density (Dr) or overconsolidation ratio (OCR), confining stress, loading history, heating direction, and drainage conditions (Campanella and Mitchell, 1968). For saturated clay and silt, several previous studies (Towhata et al., 1993; © ASCE Cekerevac and Laloui, 2004;Vega and McCartney, 2015) found that with temperature increasing (25°C to 85°C) under drained conditions, normally consolidated and lightly overconsolidated (OCR ~ 1.5 to 2) soils consistently contract. ...
Soil thermal conductivity is a function of pore water saturation, temperature, and stress level. A suction-controlled thermo-mechanical (SCTM) method has been developed to measure thermal conductivity of unsaturated soils at different temperatures (5.5°C to 75.5°C), isotropic normal stresses (35 kPa to 400 kPa), and wetting conditions. The apparatus consists of three main testing systems, including temperature-control, pressure-control, and sensor and data acquisition systems. This method permits quantification of soil thermal conductivity under the influence of stress level and temperature (i.e. construction and environmental conditions). A poorly-graded sand is used to investigate the effects of temperature and stress level on thermal conductivity of unsaturated sands. The thermal conductivity increases appreciably as stress and temperature increases at intermediate saturations (S~0.3 to 0.75). Maximum thermal conductivity occurs at 75.5°C and 400 kPa when S=0.54, where the value of thermal conductivity is about twice that at 5.5°C and 35 kPa. Hysteresis in thermal conductivity with respect to wetting-drying and loading-unloading was also observed.
... He observed that the thermal consolidation curves were similar to a conventional consolidation. Campanella and Mitchell (1968) used a cyclic thermal loading on clay and observed a minor volume expansion during cooling load. Demars and Charles (1982) among other, showed that the amount of the contraction during heating for overconsolidated clays was smaller than that of normally consolidated clays. ...
In order to fully understand the thermo-hydro-mechanical behavior of the geotechnical infrastructures, the effects of temperature variations on soil properties and soil behavior have to be studied. Hydraulic conductivity, strength, volume change, moisture content, and pore pressure generation and dissipation rates depend on temperature variations. Thermal loading might induce excess pore water pressure and volumetric changes. Temperature changes in the fine-grained soils will cause expansion in water and soil particles. Since the coefficient of expansion for soil particles is much smaller than that for water, a generation of pore water pressure is expected. This thermally induced pore water pressure and then its dissipation during the relaxation period results in a time dependent consolidation. Thermal consolidation in fine grained soil is more dominant and can be irreversible in normally consolidated clay. However, the volumetric changes of highly over consolidated soil caused by temperature increment is reversible by temperature reduction. In this research, a modified consolidation testing device is used to study the effect of temperature increments (e.g., increasing step by step temperature increments to 80ºC) on the consolidation of fine grained soils. In another words the effect of temperature increments during the test on the consolidation process is studied. Time of applying the heating, target temperature, and initial void ratio are parameters affecting the rate and the amount of consolidation in the samples.
... The former factor results in a lower retention capacity in terms of both degree of saturation and gravimetric water content because a lower surface tension of water reduces capillary pressure and the capacity of the soil to hold water (Grant and Salehzadeh, 1996). However, softening can result in a lower void ratio (Campanella and Mitchell, 1968) which can lead to two counter-acting processes: 1) increasing capillary pressure because of smaller pore sizes (Khalili et al., 2008;Gallipoli, 2012); 2) squeezing water out and reducing the total amount of water. In addition, other factors such as changes in pore water chemistry and the different thermal expansion of different phases can influence the resulting SWCC (Romero et al., 2001). ...
The dependence of the geosynthetic clay liners (GCLs) soil-water characteristic curve (SWCC) on temperature and overburden stress are characterised experimentally. It is shown that changes in void ratio and temperature alter the relationship between suction and moisture content and new forms of existing SWCC equations are developed. To cover a wide suction range, the SWCCs are measured using axis-translation and dew point methods. Based on the available experimental data, both proposed SWCCs are shown to perform well in predicting the effects of void ratio on SWCC along the drying path when compared to the experimental results. It is found that the air-entry value increases as the net vertical stress increases for the experiments under the same temperature. In addition, elevation of temperature reduces retention capacity of the GCL.
... Besides the aforementioned knowledge on the response of energy piles to mechanical and thermal loads, extensive experimental research on the behaviour of both coarseand fine-grained soils is accessible (see, e.g. Campanella and Mitchell 1968;Plum and Esrig 1969;Demars and Charles 1982;Baldi, Hueckel and Pellegrini 1988;Hueckel and Baldi 1990;Burghignoli, Desideri and Miliziano 2000;Cekerevac and Laloui 2004;Vega and McCartney 2015;Di Donna and Laloui 2015;Agar, Morgenstern and Scott 1986;Agar, Morgenstern and Scott 1987;McCartney, Xiao, Liu and Liu 2018;Zhou, Ng and Wang 2017;Ng and Zhou 2017). Based on these developments, bearing in mind that in most practical situations drained conditions are ensured throughout the heating and cooling of energy piles, the following considerations can be made. ...
Over the past twenty years, an increasing amount of research has been performed to understand the multiphysical behaviour and to address the geotechnical and structural design of so-called energy piles, i.e. deep foundations that can serve any superstructure as both structural supports and geothermal heat exchangers. The coupled application of thermal and mechanical loads to energy piles, due to their multifunctional operation, represents a challenge. Currently, knowledge about the response of energy piles subjected to thermal and mechanical loads is accessible, along with some design guidance. However, this knowledge is fragmented and no recognised performance-based design framework is available. Looking at such challenge, this paper presents a theoretical and experimental analysis of the multiphysical behaviour of energy piles, as well as a performance-based design framework for such foundations. The work highlights that thermal loads involve effects that can be neglected in the design of energy piles at ultimate limit states and can be considered relevant only at serviceability limit states. Based on this result, the performance-based design of energy piles at ultimate limit states reduces to a conventional pile design process while the design at serviceability limit states must account for a number of proposed provisions and verifications.
... Les échanges thermiques ayant lieu à travers des éléments structuraux, les déformations d'origine thermique induisent des variations mécaniques à prendre en compte dans le dimensionnement. De nombreuses études ont été menées sur le comportement thermo-mécanique des terrains (Campanella et Mitchell, 1968 ;Laloui et Cekerevac, 2008) et des pieux énergétiques (Bourne-Webb et al, 2009 ;Adam and Markiewicz, 2009 ;Di Donna et al, 2016). Du point de vue thermique, deux échelles d'étude sont possibles : l'échelle du tube échangeur de chaleur et l'échelle de l'ouvrage dans son environnement. ...
Les géostructures thermiques sont en plein développement en Europe. De nombreux projets sont en conception ou en cours de réalisation. Cet article a pour objectif de présenter une méthode d'analyse originale des échanges thermiques à long terme entre le terrain et l'ouvrage prenant en compte la circulation d'une nappe hydraulique. L'analyse des flux de chaleur par conduction et par advection est également développée. ABSTRACT-Thermoactive geostructures are in great development in Europe. Many projects are at design state or in progress. The goal of this paper is to present an original approach of long term heat exchange between the ground and the structure considering the groundwater flow. The analysis of heat flux by conduction and advection is also presented.
In the complex chemical environment of municipal waste landfills, the chemo-hydro-mechanical coupled flows in the compacted clay layer (CCL) and its deformation are very complicated. When studying the chemo-hydro-mechanical consolidation of soil, the osmotic flow, ultrafiltration, and the osmosis effect on solute migration were neglected due to the low osmotic efficiency. However, the permeability of CCL of landfill is very small, and their osmotic efficiency is higher. The osmotic phenomenon and influence of osmotic efficiency must be considered. In this paper, a 1-D chemo-hydro-mechanical coupled model of saturated soil is proposed considering osmotic efficiency. The analytical solutions of the model under specific boundary conditions were obtained by Fourier transform. The degradation model is compared with the existing governing equations and results in the literature, and the correctness of the proposed governing equations and analytical solutions is verified. Through the analysis of specific case, it can be concluded that chemo-osmotic consolidation significantly affects the consolidation of the soil layers. The osmotic consolidation leads to the generation of negative pore pressure, but it decreases with the decrease of the osmotic pressure gradient. This process leads to the rebound effect of the soil settlement. The osmotic efficiency significantly affects the consolidation characteristics of this soil layer, and therefore the effect of osmotic efficiency must be considered in soils with high osmotic efficiency.
Temperature changes are known to induce specific couplings in clay, in particular, an anomalously high thermal pressurization in undrained conditions, or a thermal compaction in drained conditions, both of which are potential threats for the mechanical stability and sealing capacity of the geomaterials. Thermodynamical analysis of those peculiar thermo-mechanical couplings points to a potentially important latent energy which in turn could limit the temperature change upon heating or cooling. The direct measurement of latent energy developed during a laboratory geomechanical test is challenging. Instead, proper identification of thermal hardening in conventional experiments with temperature changes provides an alternative route to estimate latent energy. In this work, existing laboratory thermomechanical tests of clays are analyzed with a rigorous thermodynamic framework to quantify the magnitude of latent energy in thermo-mechanically loaded clays. A thermodynamically consistent constitutive model for fully saturated clays that combines two key features: i) the temperature dependence of the blocked energy and ii) the framework of bounding plasticity, is proposed. The performance of the model is validated by reproducing results obtained in laboratory tests for Boom and Opalinus clays. The thermomechanical loads considered to validate the model performance, were then used to estimate the percentage of work that remains latent in the clayey material during plastic yielding. We find that the magnitude of latent energy is quite significant, typically a few tens of percent of the total dissipated energy, and increases significantly with temperature. Accordingly, it is expected to play an important role in the thermo-mechanical response of clays.
Thermo-active retaining walls are geotechnical structures employed as heat exchangers to provide low carbon dioxide heating and cooling to buildings. To assess the thermo-mechanical response of such structures, finite-element (FE) analyses are typically carried out. Due to the presence of heat exchanger pipes, the temperature distribution along the width of the wall is not uniform, implying that these problems are three-dimensional (3D) in nature. However, performing 3D FE analyses including elements to model the heat exchanger pipes to simulate the advective conductive heat transfer as well as thermo-hydro-mechanical coupling to reproduce the non-isothermal soil response accurately requires considerable computational effort. In this work, a novel approach to simulate thermo-active walls in 2D analyses was developed, which requires the sole use of thermal boundary conditions. This approach was found to reproduce average wall behaviour computed in 3D to a high degree of accuracy for numerous wall geometries, a wide range of thermal properties of soil and concrete, and different thermal boundary conditions along the exposed face of the wall. In addition, out-of-plane effects recorded in 3D analyses were assessed and an accurate simplified procedure to account for these when performing 2D analyses was developed.
This article presents an experimental study that examines the isotropic triaxial behaviour of tailings sands in a wide range of pressures from 10 kPa to 5 MPa, varying the fine content of the tested samples. The results suggest that the presence and quantity of fines have influence in the behaviour: there is an increase in the compressibility of tailings sands deposited in a loose state, generating significant changes in the void ratio when confined throughout the range of pressures studied. In addition, it is observed that the effect of the fines in the compressibility decreases with the decrease of the void ratio, even exhibiting stiffening of the sample for the densest conditions of confection. Results of imaging performed post-test on the material suggest that the tailings sand exhibits a slight breakage of its angular edges when consolidated at high pressures. For low void ratios, differences in fines content of up to 4% are observed for clean sand. This difference decreases when the fine content of the sand increases, suggesting that the presence of fines contributes to the stability of the granular structure, redistributing the interparticle stresses, decreasing the level of breakage.
This review summarizes various hypothetical models that were produced during last century in order to describe and simulate precisely enough the consolidation procedure in different soil types and conditions. Consolidation is a period secondary process that happens in low permeability soils and involves the rearranging of soil particles so as to dissipate excess pore pressure. The consolidation models are generally classified into two categories: the first describing large strain consolidation and the second describing small strain consolidation. The strain consolidation models remove those confinements to engage examination of much softer and looser soils without the amount of error produced by those limitations. Numerous researchers tried evolving Terzaghi's model by taking into record varieties of permeability and compressibility within the soil. For the predefined soil condition a basic and complete understanding of all the hypothetical models that is required to have the capacity to decision the model that will best fit the case under consideration. This paper also studies the influence of vibration, temperature on rate of secondary consolidation for a high organic content as well as low organic content soil.
This research aims to qualitatively/quantitively assess the effect of temperature variation on the energy pile shaft resistance. The important mechanisms by which heating can change the shear strength of clay and clay-concrete interface are evaluated using experimental and numerical methods. As for experimental method, temperature-controlled triaxial tests, constant normal load (CNL) direct shear tests and small-scale pile tests were conducted. As for numerical approach, a fully coupled thermo-hydro-mechanical (THM) analysis was performed to simulate the experimental test results so that the capability of such analysis to predict thermo-mechanical behavior of energy piles is evaluated. Reconstituted (HC-77) kaolin clay, one-dimensionally consolidated from slurry, was used in all the studies. Cyclic and monotonic heat ranging between 24° C and 34°C were applied to the clay specimen and interface. The interface was sheared under two stiffness boundary conditions; Constant Normal Load (CNL) and Constant Normal Stiffness (CNS), where the applied normal stresses varied between 100 kPa and 300 kPa. The results of experimental tests indicate that heating improves the shear strength of normally consolidated (NC) clay and NC clay-concrete interface. However, a decrease in strength of over-consolidated (OC) clays was observed, which is thought to be linked to the heat-induced change in the contact stress between clay particles. It was also found out that the increase in the strength of interface under CNL condition, which was about 10%, is exclusively attributed to heat strengthening of clay at the interface. However, the increase in shaft resistance under CNS condition (96% and 49% due to non-cyclic heating and cyclic heating-cooling, respectively) is primarily attributed to the heat-induced increase of effective lateral stress (81% and 35% due to non-cyclic heating and cyclic heating-cooling, respectively). The heat-induced increase in the shear strength of clay (8-10%) also partially contribute to the overall increase of the shaft resistance under CNS condition. It was also observed that there is very good agreement between the results experimentally measured and those numerically predicted. Therefore, fully coupled THM analysis can effectively be used to predict the thermo-mechanical behavior of real energy piles in clays.
Application of changes in temperature to soils and rocks may lead to a wide range of flow processes and physical phenomena. This chapter focuses on the fundamental aspects of coupled heat transfer and water flow in saturated and unsaturated soils and rocks, thermal pressurization of pore fluids, thermal volume change, thermal softening of the preconsolidation stress, thermal hydro-shearing, and desiccation cracking. Established applications are also presented, including energy piles, barriers for radioactive waste repositories, and thermal energy storage. Emerging research areas including the role of thermal processes in climate change and elevated temperature landfills are also discussed.
In this article, based on the rheological consolidation model of deepwater shallow sediments, the artificial samples were made in laboratory. The feasibility of artificial samples was verified by electron microscopy scanning and triaxial experiments. Deepwater shallow sediments consolidation models mainly considers two points: (i) the change of permeability with time and temperature and (ii) the effect of rheology. The consolidation experiment of deepwater shallow sediments verifies the correctness of the model. It can be found that, the artificial and natural samples have the same physical and mechanical properties. And the physical properties of natural samples can be obtained by rheological consolidation model of deepwater shallow sediments.
The two reference models for sand and clay, introduced in Chaps. 5 and 6, cover the behaviour of a variety of common soils under standard conditions. However, specific applications or specific soil types require enhancements of these models to achieve the predictive goal. A selection of such enhancements is described this chapter. The readers are introduced to methods for predicting small strain stiffness, rate effects, effects of structure, partial saturation, thermal effects and stiffness anisotropy within the theory of hypoplasticity.
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