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Stress-strain behaviour of completely decomposed granite in both triaxial and plane strain conditions
Abstract
Most of the field problems in geotechnical engineering are in three dimensional state or close to a plane strain condition. Strength and deformation properties of soils in plane strain condition are considerably different from those in an axisymmetric condition. Many researchers have investigated the behaviour of soils under a plane strain condition. However, most of the previous studies have concentrated on sedimentary type of soils like sand and clay. Our understanding on the plane strain behaviour for residual soils is less than that for sedimentary soils. A true triaxial system with four sliding rigid-plates and real time feedback control has been used to test specimens of a completely decomposed granite (CDG) soil (a residual soil) under plane strain condition. The setup of the true-triaxial rigid plates is briefly introduced first. The preparation of soil specimens and testing procedures are described. The basic properties of the CDG are presented. The stressstrain and strength behaviour of the soil obtained under plane strain condition was investigated and compared to the behaviour obtained under axisymmetric loading conditions. The results revealed that the critical state line in q-p’ space obtained under plane strain condition is the same as that obtained under axisymmetric condition. However, the critical state line in e-ln p’ space obtained under undrained plane strain condition is different from that obtained under axisymmetric condition. The peak friction angle for plane strain tests is higher than that from axisymmetric loadings. It is also found that shear bands occur only in drained plane strain compression. Defuse bulging is the mode of failure for undrained plane strain as well as triaxial loading.
... Simple shear condition in soil mechanics refers to a state whereby the soil sample undergoes shear stress on the top and bottom surface of the sample without any shear stress induced on the lateral sides of the sample. Quite a number of infrastructures such as dams or reinforced slopes have very large lengths compared with their other dimensions (Xu et al. 2020;Kumruzzaman & Yin 2012;Li et al. 2014). Many cases involving stability of embankments and cuts for roads and strip footings eventually represent a plane strain condition whereby we could not observe any deformation taking place in the direction at right angles to the displacement (Zhao 2017;Terzaghi et al. 1996). ...
This paper presents the experimental work on typical Malaysian silty residual soils in order to evaluate fundamental soil properties in particular its stiffness under low frequency cyclic loading. There has been very little information on local silty residual soils which is very important for local geotechnical design purposes. Lack of such information contributes to the dependency of foreign soil data which might not be representative of local silty residual soils. This study departs from the basis of there have been verified evidences that we are not spared from seismic activity in Malaysia. Hence, it would be misleading if we were to exclude soil properties under cyclic loading for design purposes in Malaysia. This research revolves around the development of simplified device to evaluate the stress-strain behaviour of soils under simple shear strain conditions. The cyclic loading test results on Malaysian sedimentary residual soil sample exhibit increase of drained shear stiffness, GSTIF and gained strength after 30 cycles indicating cyclic hardening behaviour. It is evident that magnitudes of cyclic load and cyclic displacement influences the rate of soil volume change. Nevertheless, the densification of soil samples due to increment of cycles caused reduction in volume change. It is foreseen that the obtained parameters could assist in the practical geotechnical engineering problems related to cyclic conditions.
... The angle of internal friction of sands from direct shear tests is often reported to be higher compared to the triaxial compression tests [21][22][23]. This is the case for rice husk as plant aggregate. ...
The return to old building methods by mixing crop by-products with mineral binders is arousing great interest in Europe since about 25 years. The use of these bio-aggregates based materials for the design of building envelopes is a valuable opportunity to deal with increasingly demanding thermal regulations. In addition, the regulatory framework is moving towards reducing the overall car-bon footprint of new buildings. Some traditional and historic buildings are based on timber framing with earth-straw as infill material for instance. Hemp concrete is a bio-based material that can be manually tamped in timber stud walls or more recently in the form of precast blocks. Owing to their low compressive strength, bio-based concretes using a large volume fraction of plant-derived aggregates are only considered as thermal and sound insulation materials. The structural design practice of wood frame walls does not assume any mechanical contribution of hemp concrete whereas it may contribute to the racking strength of the structure. In this context, more research is needed regarding the shear behavior of crop by-products and bio-based concretes. In this case, the objective of the study was to perform direct shear tests under three levels of normal pressure on hemp shiv and rice husk as unbound crop by-products. The results showed that the friction angle of the granular skeleton based on rice husk for a given relative displacement was significantly lower than that measured on hemp shiv. This is in accordance with what had been observed on bio-based concretes cast by mixing aggregates with lime and shear strength parameters measured by means of triaxial compression.
... Mechanical behavior of rock specimens under biaxial and triaxial loading conditions was studied by some researchers (Yumlu and Ozbay 1995;Labuz et al. 1996;Kumruzzaman and Yin 2012;Zhao et al. 2015). Their experimental results showed that the loading conditions such as biaxial loading and triaxial loading might have an influence on the peak strength and the post-peak behavior of rocks. ...
Rock strength and deformation behavior has long been recognized to be closely related to the microstructure and the associated micro-cracking process. A good understanding of crack initiation and coalescence mechanisms will thus allow us to account for the variation of rock strength and deformation properties from a microscopic view. This paper numerically investigates the micro-cracking behavior of Bukit Timah granite by using a grain-based modeling approach. First, the principles of grain-based model adopted in the two-dimensional Particle Flow Code and the numerical model generation procedure are reviewed. The micro-parameters of the numerical model are then calibrated to match the macro-properties of the rock obtained from tension and compression tests in the laboratory. The simulated rock properties are in good agreement with the laboratory test results with the errors less than ±6%. Finally, the calibrated model is used to study the micro-cracking behavior and the failure modes of the rock under direct tension and under compression with different confining pressures. The results reveal that when the numerical model is loaded in direct tension, only grain boundary tensile cracks are generated, and the simulated macroscopic fracture agrees well with the results obtained in laboratory tests. When the model is loaded in compression, the ratio of grain boundary tensile cracks to grain boundary shear cracks decreases with the increase in confining pressure. In other words, the results show that as the confining pressure increases, the failure mechanism changes from tension to shear. The simulated failure mode of the model changes from splitting to shear as the applied confining pressure gradually increases, which is comparable with that observed in laboratory tests. The grain-based model used in this study thus appears promising for further investigation of microscopic and macroscopic behavior of crystalline rocks under different loading conditions.
... The occurrence of one or another kind of failure mode has to be analysed. According to some authors [47,48], both failure mode and shear band formation mainly depend on porosity, particle size and shape, specimen density and confining pressure. In the present study, it is assumed that the density gradient along the length of the specimen is responsible for bulging and crushing of the lower part of LHC specimens. ...
... Due to world-wide distributions and extensively used as construction materials, many research worked have already been done on residual soils. For example, the engineering characteristics, microfabric and mineralogical composition, degree of weathering, compressibility and shear strength properties and their controlling factors, bonding behavior and its loading impact, stiffness or yielding behavior of both natural and compacted residual soils are examined by numerous scholars [1][2][3][4][5][6][7][8][9][10][11]. Several geo-engineering problems associated with residual soils such as landslides, subsidences, damage of road and railway tract, building collapse in many parts of the world have also been reported. ...
... Due to world-wide distributions and extensively used as construction materials, many research worked have already been done on residual soils. For example, the engineering characteristics, microfabric and mineralogical composition, degree of weathering, compressibility and shear strength properties and their controlling factors, bonding behavior and its loading impact, stiffness or yielding behavior of both natural and compacted residual soils are examined by numerous scholars [1][2][3][4][5][6][7][8][9][10][11]. Several geo-engineering problems associated with residual soils such as landslides, subsidences, damage of road and railway tract, building collapse in many parts of the world have also been reported. ...
Due to worldwide distributions and extensively used as construction materials, geotechnical engineers are interested in understanding the mechanical behavior of residual soils which are sometimes referred in the literature as problematic soils. The climatic zones where residual soils occur are often experienced by many drying-wetting cycles due to seasonal variations. This seasonal variation in the water content termed as drying-wetting cycle is regarded as the most destructive environmental factor that may cause many foundation diseases. Considering these, the purpose of this study is to understand the effects of drying-wetting cycles on saturated shear strength characteristics of undisturbed residual soil. A series of consolidated drained (CD) triaxial tests are conducted on multiple drying-wetting soil specimens to analyze the saturated shear strength. The test results indicate that the stress-strain relationships appear to be strain-hardening. The deviatory stress and initial stiffness of saturated soils increase and the volume of soils becomes contractive as the net normal stress increases but decrease with increasing drying-wetting cycle numbers. The cohesion (c d) and internal friction angle (φ d) decrease with increasing cycle number (N) but the attenuation rate of φ d is less than c d. The variations of c d and φ d with respect to drying-wetting cycles can be expressed by exponential function. The saturated shear strength and it's attenuation rate due to drying-wetting cycles are analyzed. The effect is more significant for the first cycle and decreases with subsequent cycles and finally reaches to a constant state after 4 cycles. Furthermore, a mathematical function is proposed in this paper which can describe the saturated shear strength attenuation rate of drying-wetting cycle samples. Such studies are useful to understand the possible changes in shear strength behavior of residual soils below the engineering structures that are subject to periodic drying and wetting from climatic variations.
... Masado is distributed in large areas of land reclamation and coastal regions and the sample for this testing was taken from the region near Ota River in Hiroshima prefecture, Japan. Masado has also been employed in laboratory tests by many researchers [26][27][28]. ...
A series of one-dimensional compression tests have been carried out on three kinds of granular materials in a dense state to investigate their mechanical and crushing behaviours. A new testing apparatus that can simultaneously measure the axial and lateral stresses acted on the cylindrical specimen was also de- veloped. Experimental results show that the break-point stress on e - log p curve is the largest for glass beads ballotini. A rise in compression index with the increasing axial load is observed for all three granular materials. The lateral earth pressure coefficient at rest Ko for the three granular materials slightly in- creases with the increasing axial load and attains a steady value between 0.25 and 0.3 at the initial loading stage. The value for Ko markedly increases as the axial load is removed during the unloading process. The axial strain of Masado is the largest at the same axial load level due to its mineral hardness. Experimental results demonstrate that the crushing degree of granular material is greatly influenced by the loading modes and conditions.
... Crushing failure of relative crushable granular material initially occurs at relatively low stress level and displays significantly contractive behaviour with increasing external force. [20][21][22] in laboratory test. Chi-ibishi sand is a skeletal carbonate beach sand from Okinawa, Japan. ...
Particle crushing dominates the deformation behaviour of granular materials under significantly high compressive and shear stress. A proposed constitutive model has been verified to predict crushing behaviour of granular materials with different crushability and adopted one kind of reference crushing stress. It is noted that no positive dilatancy of granular material in triaxial test occurs once the confining pressure exceeds a certain stress level. That stress is defined as the reference crushing stress. This study presents a parametric study on the reference crushing stress in the constitutive model and examines its variation for different distributed ranges of grain size gradation and relative densities. Predicted results demonstrate that the peak stress ratio increases and contractive behaviour becomes less obvious with a larger reference crushing stress. Reference crushing stress increases with a wider grain size gradation and larger relative density for the same granular material. A linear relationship between the reference crushing stress and single particle strength has been obtained from the numerical and experimental results. The reference crushing stress can be recognized as one effective index to evaluate the strength of granular material in triaxial tests.
The use of jet grouting to stabilize a sloping berm in an excavation is uncommon. In a pseudo top-down construction project, after the installation of the diaphragm walls, bulk excavation took place at the central part with 1:2 sloping berms formed at the north and south ends, and with 1:2 and 1:4 sloping berms supporting the diaphragm walls at the east and west ends. Bottom-up construction was then carried out at the central core and by top-down construction at the periphery. As the site has a complex history of reclamation and land use, in areas where the marine clays are thick and/or weak, JGCs had to install to improve the stability of the sloping berms. Several rows of 2 m diameter JGGs at 4 m c/c spacing, serving as dowels, were installed through the marine deposits and alluvium with 2 m into reclamation fills above and 0.5 m nominal depth into completely decomposed granite below. Conventional design principles and parameters following the local codes of practices were adopted. The interaction of the diaphragm wall, slope and JGCs was simplified for a two-dimensional PLAXIS model analysis and the probable failure mechanisms were examined. The deflection of the diaphragm wall panels and JGCs, the ground water table in front of and behind the diaphragm walls were monitored as the excavation progressed. In this paper, a representative design section is presented and the performance of the lateral support system is compared with the design prediction. The actual movement of east wall is found larger than the conventional analysis of the movement around an excavation using values of elastic modulus equal to two times the elastic modulus of soil (E), i.e. 2E. This is consistent with the model findings that the mode of straining within the final form of the slope is predominantly by shearing rather than by direct straining. The deformation is therefore controlled largely by the value of shear modulus (G) within the slope, and the use of 2E would underestimate the predicted movement. Indifferently, the actual movement of west wall is close to the prediction using 2E because the sloping berm is wide and the mode of straining of the soil within the slope is predominantly by direct straining instead of by shearing.
In Malaysia, many parts of the superficial ground are covered with highly-weathered tropical soil, which has a relatively low permeability and is usually partially saturated. Although its engineering properties are of paramount importance for geotechnical applications, performing detailed triaxial test to obtain precise effective stress mechanical behaviour using fully-saturated specimen is very difficult and the testing procedure needs more improvements. The present study deals with the mechanical behaviours of a residual soil in Malaysia by using an improved procedure for triaxial test for specimen saturation and effective stress path loading. A series of undrained compression and extension triaxial tests, including CIUC, CIUE, CKoUC, and CKoUE, were conducted on normally-consolidated saturated soil specimen. The effective stress paths for CIUC and CIUE tests were nearly identical to each other when the specimens are consolidated beyond 100kPa. Although numbers of tests are limited, the CKoUC and CKoUE produced effective stress paths showed typical one for normally-consolidated soil as reported by others. In the Ko consolidation test, a constant value of Ko = 0.31 or 0.34 was obtained after the soil specimen reached normally-consolidated state. The experimentally-obtained Ko value was in good agreement with the computed Ko value based on the Jaky's equation with obtained friction angle.
In this paper a new plane-strain apparatus is described. The main feature of the plane-strain apparatus is that the intermediate principal stress can be measured by four submersible pressure transducers. Experimental data obtained from drained tests on very loose to medium dense sand are presented. The strength and deformation behavior of the sand under plane-strain conditions and shear band formation are studied. The results show that the failure envelope obtained from plane-strain tests is lower than that from triaxial tests. However, in terms of friction angle, the value obtained from plane-strain tests is higher than that from triaxial tests. The critical state line obtained under plane-strain conditions is also different from that under axisymmetric conditions. Under plane-strain conditions, shear bands occur for medium loose to dense specimens. However, no visible shear bands are observed for very loose specimens. This is consistent with the study reported by Han and Vardoulakis ͑1991͒ but different from that by Finno et al. ͑1996, 1997͒.
Experimental results are presented which characterize the behaviour of a loos, fine-grained, water-saturated sand tested under globally undrained and drained conditions in a plane strain apparatus. The objective of this investigation is to provide insight into the phenomenon of shear banding in loose sand. Together with local measurements of boundary forces and deformations, stereophotogrammetry is used to investigate the progression of strain localization in plane strain compression. Typical results and findings concerning the evolution of non-homogeneous deformation are presented in detail. Shear banding occurred in both undrained and drained experiments on loose masonry sand. In general, temporary modes of strain localization, abserved during macroscopically 'uniform' deformations of a specimen, gave way to a single, persistent shear band. A clear pattern of onset of the formation of the persistent shear band, mobilization of the maximum effective friction and complete formation of the band was observed in all tests. The stress state when the localization begins is very close to, yet precedes that corresponding to the maximum mobilized friction. The persistent shear bands evolve with changing width and orientation.
A comprehensive experimental investigation was conducted to investigate the effects of loading condition and confining pressure on strength properties and localization phenomena in sands. A uniform subrounded to rounded natural silica sand known as F-75 Ottawa sand was used in the investigation. The results of a series on conventional triaxial compression (CTC) experiments tested under very low-confining pressures (0.05-1.30) kPa tested in a microgravity environment abroad the NASA Space Shuttle are presented in addition to the results of similar specimens tested in terrestrial laboratory to investigate the effect of confining pressure on the constitutive behavior of sands. The behavior of the CTC experiments is compared with the results of plane strain experiments. Computed tomography and other digital imaging techniques were used to study the development and evolution of shear bands.
Three different principal streses can be applied in fixed directions to a cubical specimen in this apparatus. The requirements and the construction and operation principles for the cubical triaxial apparatus are presented. The loading system and the deformation measurement principles are described, and procedures for preparing sand and clay specimens are presented. The advantages and limitations of the apparatus are discussed. The apparatus is relatively inexpensive to build, and it fulfills all basic requirements for high quality soil testing in three dimensions.
A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.
Description
First publication of its kind in 25 years, this 900-page volume serves as an engineer’s guide for triaxial testing. Subjects include: equipment, test methods, and test interpretation and errors, and new test varieties.
To achieve a direct measurement of the flow function essential to the design of silos, measurements of the major principal stress during steady state yield and the corresponding strength in the unconfined compression are required. A new plane strain biaxial tester based on flexible boundaries, has been developed for this measurement. Advantages normally associated with rigid boundary apparatuses have been achieved by matching the displacement of a pressure bag with controlled movement of the pressure bag backing plate. A make and break contact sensor is used in each lateral pressure bag to achieve this. Preliminary direct measurements of the flow function of a calcite powder give results similar to data obtained by Jenike shear cell measurements.
The mechanical description of a new plane strain (biaxial) apparatus for soil testing is presented. The design took into consideration flexibility in accomodating different specimen sizes, easy assembly procedure, and well-controlled boundary conditions. The apparatus is well instrumented with load, displacement, and pressure sensors and has the capabilities to capture localization and shear band development. A comparison between two experiments that were conducted on F-75 Ottawa sand is presented and the effect of inhibiting lateral movement of bottom end platen is presented and discussed. It has been found that restraining lateral movement of bottom end platen has resulted in higher peak and residual load values.
The triaxial test has been widely accepted for design problems and for research in soil mechanics since it was improved and popularized in the forties. There are many sound reasons for its wide popularity including, of course, the fact that numerous important structures were designed and stand securely after many years, their construction based on soil strength data obtained from the triaxial test.
Anisotropic parallel alignment of particles is universally observed not only in river, beach and coastal dune sands but also in artificially deposited sands. Anisotropic shear strength caused by the anisotropic parallel alignment of particles can be observed more clearly in the plane strain condition ε2=0 than in the symmetrical stress condition σ2=σ3. This must be chiefly due to the fact that re-arrangement of particles during shear deformation can be more easily performed in the latter condition than in the former one. Shear strength of sand in a plane strain test has been generally believed to be 10% to 20% greater than that obtained in a triaxial compression test. When the specimen is compressed at a small angle to a bedding plane, however, it is possible that the shear strength in the plane strain test is smaller than that in the triaxial compression test. The effect of anisotropic shear strength cannot be ignored when stability problems and earth pressure problems in plane strain condition are analyzed.
The development of localized strains (shear banding) in soils near peak stress levels and the subsequent continued deformation within shear bands during observed softening render important issues such as critical state difficult to investigate. The determination and overall validity of critical state behavior in sand is of considerable importance, as it provides the basis both for failure criteria/postfailure behavior of many constitutive models and for stability analysis. A series of drained plane-strain experiments on sand specimens with detailed local analysis was carried out to investigate the evolution of stress state and void ratio, as well as the uniqueness of critical state. Persistent shear bands form at the peak effective stress ratio; subsequent strain softening behavior occurs in concert with localized deformation with the shear band A unique critical stress state was found to exist for a given confining stress; however, the test results indicate that there is no unique relationship between void ratio and confining stress at the critical state.
The strain softening of a granular soil under a σ1′ ≠ σ2′ ≠ σ3′ condition and along a wide spectrum of paths was investigated experimentally. To ensure that the observed behaviour was not an aberration due to boundary imperfections, a specially designed multi-axial cell was used. Microprocessor control of both stress and strain paths was incorporated into the testing programme. In particular, strain path testing where the strain increment ratio dεr/dε1 was controlled to a specified value was used extensively. A photographic technique was used to detect the initiation of shear band. Strain softening was found to be path-dependent. It can take the form of shear band formation, or it can occur without the devleopment of any non-homogeneity. Shear band formation is not neccessarily a consequence of boundary imperfections, but can occur as the inevitable response of a sample to certain stress states and shear paths. The conditions for shear band formation were established and three types of strain softening identified.
Since decomposed granite soil shows various characteristics of shear behavior dependent on initial conditions such as weathering degree and grain breakage, it is necessary to investigate changes of shear characteristics for different initial conditions. Direct shear tests and triaxial compression tests(¯C¯U, CD) were carried out in this study for undisturbed and compacted decomposed granite soils obtained from 3 construction work sites with the various weathering degree and components of parent rocks. Regardless of degree of weathering, the deformation behavior of undisturbed samples under low confining stress become hardening to softening as overconsolidated clay. Whereas compacted decomposed granite soils did hardening-constant as sedimentary clay. In CD tests for undisturbed samples, it turns out possible that strain increment ratio( dυ/dε) is expressed as linear form α(M – η), i.e. dυ/d ε = α(M – η).
Specimens of a saturated, undisturbed marine clay were consolidated and subsequently sheared under triaxial and plane strain conditions using a variety of stress paths and drainage conditions. It was found that both the undrained strength and the angle of shearing resistance were slightly larger in plane strain than under the corresponding triaxial conditions. Methods to estimate strains in undrained plane strain shear from the results of triaxial tests under identical stress paths have been developed.
This article presents a testing study on the strain-rate effects on the stress--strain behavior of natural, undisturbed Hong Kong marine deposits (HKMD) from three Hong Kong locations, including a one-dimensional (1-D) compressibility in a confined condition, and undrained shear strengths in triaxial compression and extension modes. The influences of the strain rates on the one-dimensional compressibility are studied by means of constant rate of strain (CRS) tests and multistage loading oedometer (MSL) tests, and those on the undrained shear strengths are studied by Ko-consolidated undrained compression and extension tests with step-changed axial strain rates (CKoUC and CKoUE tests), and with both step-changed axial strain rates and relaxation processes (CKoUCR and CKoUER tests). The strain-rate effects on the stress--strain behavior are generally examined by “apparent” preconsolidation pressures in the 1-D compressions and undrained shear strengths in the triaxial compression and extension stress states. The stress--strain behavior of the natural, undisturbed HKMD exhibits considerable viscous characteristics. In the CRS and MSL tests at a given strain, the higher the strain rate, the higher the effective stress, the higher the porewater pressure. In the undrained shearing tests, the higher the strain rate, the higher the undrained shear strength, but the lower the porewater pressure. For the CKoUC and CKoUE tests on the Tsing Yi site samples, the undrained shear strength increases by 8.5% and 12.1% for one order increment of axial strain rate of 0.2%/hr (i.e., ρ0.2) for the compression and extension modes respectively. For the CKoUCR and CKo tests on the Tung Chung site samples of different compositions, average ρ0.2 is increased by 6.2% for the compression and 9.5% for the extension, but by 18.8% for the extension on a higher plastic sample. The present study shows that the strain-rate effects on the stress--strain behavior of the undisturbed HKMD are larger for specimens in extension than those in compression.
Decomposed granitic soil is widely used as the subgrade material in Korea. The mechanical behavior of the soil can differ depending on the fine aggregate content of the soil. Due to particle crushing during loading and compaction, the soil may behave as either cohesive or cohesionless. In order to evaluate the effects of fine aggregate content on the mechanical properties of the compacted decomposed granite soils, the direct shear test, the triaxial shear test as well as some fundamental property tests were made by using samples with the five different fine aggregate contents of 10, 20, 30, 40, and 50% by weight. Results of the triaxial tests showed that as the percentage of the fine aggregates decreased, the cohesion decreased as well as the internal friction angle increased. In the direct shear test, the soils containing lower amount of fine aggregates exhibited that the shear strength was considerably reduced after it reached the peak value. Comparably, soils with the high fine aggregates showed that the shear strength was quite constant after the peak strength. The critical state friction parameter showed that the parameter decreased with an increase of the fine aggregate content. Results of the triaxial and direct shear tests indicated also that the fine aggregate content of 30% could be one indicator for soil materials behaving either as sand or as clay materials. Thus fine aggregate content, less than 30% by weight, could be more obtainable for the subgrade materials when leading also to the increased stability of the roads. With the lower fine aggregate content the soils then also show similar and better characteristics of sands not clays. Further studies are recommended on understanding of the mechanical behavior of the decomposed granitic soils.
A study of strain localization in triaxial tests on s and, using computed tomography is reported. The inception and the development of the localization are detected and described, both qualitatively and quantitatively. The complex g geometrical structures involved in the localization patterns are described and the local void ratio evolution in the localization zone(s) is determined. Dense and loose Hostun RF sand specimens were tested under a confining pressure of 60 kPa. It is shown that strain localization can occur in different localization patterns depending on test conditions; a mechanism involving, simultaneously, a central cone and a set of planes in pairs was found for many of the specimens tested. The comparison of the local void ratio evolution in the shear zones with the global void ratio measurement supports the important conclusion that a limit void ratio is reached in the shear zones. This ratio is significantly different from the final void ratio d defined from the global measurements; the lack of physical releveance of the latter is established.
Pre-failure plastic deformation is modelled as a process controlled by simultaneous plane strain hardening and plane strain softening associated with no-extension directions and maximum stress obliquity planes. The model defines the orientations of thin rupture layers which may form at failure and suggests the possible form of a hardening law and yield surface. Data in agreement with the model are presented from seven different shear apparatuses and a range of plane strain model tests.
Differences in the strength and deformation characteristics in plane strain compression between different batches of two sand types were critically evaluated. Two types of plane strain apparatuses were used. Large differences were observed between different batches of each type of sand, pet virtually no differences were found in particle physical properties including gradation, specific gravity, minimum and maximum void ratios, particle shape, and crushability. For each type of sand, differences in the measured peak strength between two types of plane strain tests were very small when effects of several possible influencing factors were accounted for. The prepeak dilatancy characteristics were noticeably different between the two types of plane strain tests, but the reason(s) could not be identified. The trend of inherent strength anisotropy was found to be very similar for the two plane strain apparatuses, but did depend on the sand type.
A biaxial compression apparatus for investigating shear-band formation and growth in dry and water-saturated sand and clay specimens is described. This apparatus is a modification of the device designed by Vardoulakis and Goldscheider [1] for testing planar shear banding in sands. The modifications involve improved axial load guidance, low friction linear bearing, and enhanced load and displacement measurement instrumentation. The apparatus allows for accurate prelocalization material behavior and shear-band growth investigation. Specimen preparation and data evaluation procedures are described, and test results on dry Ottawa sand are presented.
The effect of stress path on the steady state line of a liquefiable sand is investigated. Results from undrained triaxial compression and extension tests on water-deposited sands show that the steady state line of a given sand, though unique in the effective stress space, is not so in the void ratio - effective stress space. The sand is contractive over a much larger range of void ratios in extension than in compression. While a single steady state line emerges for compression loading, extension loading yields several lines, each characteristic to a given deposition void ratio. All these extension lines lie to the left of the compression line in void ratio - effective stress space. Thus at a given void ratio, steady state strength is smaller in extension than in compression, the difference increasing as the sand becomes looser. The implications of the results are discussed in relation to practical design. -Authors
A series of drained biaxial compression tests were conducted on two sands to determine the effects of consolidation history on their critical states. Specimens of each sand were consolidated along at least two separate paths in void ratio-effective stress space, creating several unique consolidation histories. Because the sands were dilative, strains localized during shearing and the evolution to critical state occurred only within the shear band. Digital images were obtained through a plexiglass sidewall throughout each test. Digital image correlation techniques were used to quantify the displacements within the band, and a linear regression technique was used to formulate a displacement function from which strains were computed. The critical state was achieved within the shear band in each test, but the critical state line was found to depend on the initial state and subsequent consolidation history of the sand specimens.
This Paper presents the results from an experimental study of the pre-failure and post-failure behaviour of water-saturated fine-grained sand in biaxial compression. Tbe experiments were performed in a plane-strain apparatus which allowed a detailed study of bifurcation and post-bifurcation pbenomena. Emphasis is given to limiting states, deformation instabilities and failure phenomena (liquefaction and localization). A patterned failure mode is illustrated witb X-ray radiographs. Internal fluid flow and rate senstitivity in relation to mathematical stability are also discussed.
Cet article présente les resultats d'une étude expérimentale du comportement avant et après rupture d'un ébantillon de sable fin saturé soumis à une compression biaxiale. La cellule biaxiale maintient I'écbantillon en deformation plane, ce qui permet une étude detailée des phénomhnès de bifurcation et de post-bifurcation. Dans cette étude expérimentale, on a mis I'accent sur les questions d'état limite, d'instabilité de déformation ainsi que sur les pbénoménes de rupture (liquéfaction et localisation). Un mode de rupture en franges est mis en évidence à I'aide d'une technique d'auscultation par rayon-X. Les questions d'éoulement interne du fluide et de la sensibilité à la vitesse de l'essai sont également discutées en relation avec les problèmes matbématique d'instabilite.
Results from a series of biaxial undrained tests on a fine, angular, quartz sand (Hostun FR) are presented. Both dilative and contractive specimens were tested. Strain localization in the specimen was recorded using a false relief stereophotogrammetric method, which allows a full-field measurement of the incremental strain within a specimen throughout the test. Incremental strain maps are obtained at different states on the stress–strain response. It is shown that shear banding can take place in both contractive and dilative specimens, but for the latter the onset of localization is delayed until cavitation takes place in the pore-fluid. It is concluded that in dilative granular media, non-drainage can preclude localization as long as cavitation in the pore-fluid does not relax the isochoric constraint. Copyright © 1999 John Wiley & Sons, Ltd.
Experimental results are presented from the extensive program of drained plane strain compression tests on sand carried out in Grenoble over the last two decades. Systematic analysis of photographs of the deforming specimen allowed for measuring deformations and determining strain fields throughout the test, that is: prior to, at, and after the onset of strain localization. The principles, details and accuracy of the procedure are described, as well as its suitability to properly depict the patterns of deformation. Findings concerning the occurrence and progression of strain localization are discussed. The issues of shear band orientation and thickness are addressed, as well as temporary and persistent complex localization patterns, and the volumetric behaviour inside a band after its formation. The influence of such variables as initial state of the sand (effective stress and relative density), specimen size and slenderness, as well as grain size, is discussed. Copyright © 2004 John Wiley & Sons, Ltd
The paper presents a comparison between the behavior of slurry-consolidated Kaolin specimens tested under axisymmetric Conventional
Triaxial Compression (CTC) and Plane Strain (PS) loading conditions. The PS experiments were conducted on an instrumented
apparatus capable of capturing the onset of shear bands. The specimens were consolidated and then sheared under undrained
condition. The PS specimens failed via a well-defined shear band that began to develop during the hardening stress regime
whereas CTC specimens failed through a diffuse bulging mode. The undrained shear strength (S
u) of CTC experiments is smaller than the S
u of PS experiments. However, the normalized S
u of CTC experiments is very close to PS1, which was consolidated under similar K
o condition.
The localization of deformation in laboratory tests on granular material is considered. This paper is concerned with experimental results obtained with two different sets of apparatus on dry dense sand. In the first, a true triaxial apparatus, some unexpected combinations of shear band mechanisms are shown, leading to “hidden” localization; in the other, a biaxial apparatus, a complete description of the incremental strain fields at the localization inception, and afterwards, is given. The initiation and the propagation of the shear bands are discussed, and the dilatancy effects are outlined.
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