Direct Simple Shear Tests Research Articles

Investigation on shear modulus and damping ratio of Algiers marls under cyclic and dynamic loading conditions

A sound knowledge of the dynamic properties of soils is needed to solve several geotechnical engineering problems associated with earthquakes. Here we describe a laboratory investigation performed to measure the dynamic properties of the Plaisancian deposit of marls in the Algiers region using cyclic triaxial tests, cyclic double specimen direct simple shear tests, cyclic torsional shear tests and dynamic resonant column tests. The key parameters governing the nonlinear soil behavior under cyclic/dynamic loading and their relative importance in terms of affecting the dynamic properties of soils, wich are communaly represented by the normalized equivalent shear modulus reduction and damping ratio curves, are illustrated and discussed. We also address the differences in the deduced parameters obtained with different tests, procedures and interpretation criteria. The comparison between test results and empirical or semi-empirical relations for normalized equivalent shear modulus and damping ratio curves highlights a number of limitations and shortcomings of predictive models currently widely used.

Response of natural fine-grained soils for seismic design practice: A collection of research findings from British Columbia, Canada

This paper summarizes the results from a comprehensive laboratory experimental research program conducted at the University of British Columbia, Canada to study the mechanical behavior of natural fine-grained soils. Constant-volume direct simple shear tests were performed on natural silt samples collected from various locations in British Columbia to investigate the monotonic and cyclic shear loading response of these materials. Influencing factors such as effective confining stress, over-consolidation ratio, initial static shear bias, soil plasticity, and soil fabric/micro-structure on the mechanical behavior of silts were systematically investigated using a series of controlled laboratory tests. The key observations arising from these examinations are presented and discussed to serve as input for the development and/or refinement of design practice approaches for seismic geotechnical design. New directions to be considered to advance the current state of understanding and knowledge on the mechanical behavior of natural fine-grained soils are identified.

Test fill brought to failure on soft plastic marine clay at Onsøy, Norway

A test fill at Onsøy, close to the town of Fredrikstad in Norway, was built on a very soft marine clay with in situ vane strength as low as 11 kPa and a plasticity index varying from 34 to 50. The dimensions at the bottom of the long test fill were 20 m × 60 m with a height of 2.3 m. The fill, as placed in the first stage, had a computed factor of safety against foundation failure of 1.35 based on in situ vane strength. The fill was allowed to sit for about 3 years (from 1972 to 1975) before it was, in a second stage, brought to failure in about 4.3 days by raising the height. This second stage is the subject of this paper. Back-calculation of the failure by undrained stability analysis based on in situ vane tests performed shortly before the start of the second stage, based on undrained triaxial and constant volume direct simple shear tests on specimens from tube samples taken shortly before the start of the second stage and reconsolidated to the in situ effective stresses, gave factors of safety varying from 0.88 to 1.45 depending on type of analysis. Settlement values computed at the centreline of the fill for the second stage based on the results from undrained compression triaxial tests agreed reasonably well with the field measurements.

Development of a Large-Size Cyclic Direct Simple Shear Device for Characterization of Ground Materials with Oversized Particles

Abstract Direct simple shear (DSS) testing, despite its limitations, is one of the most common laboratory element tests in geotechnical engineering practice. The development and validation of a 300-mm diameter DSS device as well as test data generated for two materials with oversized particles, specifically pea gravel and municipal solid waste, are presented. The device has the capability to execute shear wave velocity measurements using both bender elements and accelerometers, as well as monotonic and cyclic testing under constant load or constant volume conditions. Validation testing using Ottawa sand C109 confirmed that the monotonic and cyclic constant volume response of the sand using the large-diameter device was similar to the results presented using conventional-sized DSS test devices. The shear wave velocity measurements using bender elements and accelerometers were found to be practically identical for the tested sand and pea gravel and were also consistent with data reported in the literature. The importance of axial (or vertical) displacement control during constant volume shearing is emphasized. It was found that tests that meet the ASTM D6528-07, Standard Test Method for Consolidated Undrained Direct Simple Shear Testing of Cohesive Soils, threshold of 0.05 % maximum axial strain during shearing may still result in different constant volume response, and it is recommended that (a) the threshold is changed to a maximum of 0.025 % and (b) the evolution of axial strain during constant volume shearing is always reported.

Effects of gas hydrates dissociation on clays and submarine slope stability

Gas hydrate dissociation is often considered as a precursor or triggering factor for submarine slope failures occurring in relatively deep waters where the bulk of the gas hydrate is found in fine-grained sediments. However, there are actually relatively few studies that focus on the effect of gas hydrate dissociation on the behavior of clays, and very few on what physically happens to clay during and after the dissociation process and how gas hydrate dissociation affects the geotechnical properties of clays. In this paper, we illustrate the effects of hydrate dissociation in clays from laboratory strength tests (direct simple shear) combined with visualization including very-high-resolution 3D imaging (computed tomography), using R11 as the hydrate forming fluid in both laponite and Onsoy clay. The test results reveal that the hydrate dissociation creates bubbles in the surrounding clay matrix and around pipe/well models. In addition, we use CO2-saturated water as the pore fluid in soft clay, and test results show that cracks may develop, allowing gas migration to take place after reducing back pressure in an oedometer cell. Direct simple shear tests show that the undrained shear strength decreases by up to ∼15% due to this process. The test results were then implemented in a 2D finite element model to assess the influence of hydrate dissociation on submarine slope stability. We chose a slope segment west of Svalvard—an area where methane gas bubbles escape from the seabed. The gas bubbling in this area is likely due to climate-controlled hydrate-dissociation (warming of bottom water masses). In the finite-element model, we include the change of methane hydrate stability zone (MHSZ) with time as well as the hydrate-dissociation-induced failure zone, which may be a potential leakage pathway. The numerical study indicates that the hydrate dissociation caused by bottom water warming is unlikely to be the main cause generating a leakage pathway or failure plane. However, the hydrate dissociation causing the reduction in shear strength facilitates a potentially unstable condition. The results imply that the hydrate dissociation may contribute to slope failure as a secondary driver, but are unlikely the main driving force. The aim of this study was to improve our understanding of the physical processes of gas expansion, migration and effect of hydrate dissociation through visualization and a finite element model. In addition, this study discussed methods to detect gas hydrate through a case study, and it was found possible to predict average gas hydrate saturation at sites where the sulfate-methane transition depth is known.

Cyclic Direct Simple Shear Test to Measure Strain-Dependent Dynamic Properties of Unsaturated Sand

The dynamic properties of a clean sand under different degrees of saturation were investigated using a modified custom built Direct Simple Shear (DSS) apparatus at the University of New Hampshire. The specific characteristics of the DSS were presented, and the testing procedures were discussed. The device used the axis translation and tensiometric techniques to control the matric suction in the soil specimen. The investigation on F75 Ottawa Sand showed a decrease in shear modulus and an increase in damping by increasing the shear strain over the tested range of strains for various degrees of saturation: dry, saturated, and partially saturated. The modulus reduction in the applied range of medium shear strains regardless of the degree of saturation demonstrated the capability of the DSS in consistently capturing the changes of dynamic properties. Experimental results indicated that the matric suction can have a substantial effect on the stiffness of the soil. However, the extent of this effect may depend on the induced strain level of the effective stress in unsaturated soil. In addition, partially saturated specimens resulted in lower dynamic compression.

Macro- and micromechanical evaluation of cyclic simple shear test by discrete element method

Direct simple shear tests are considered to be simple laboratory tests that are capable of imposing a cyclic loading that is analogous to that induced by earthquakes. A realistic evaluation of the test results demands a profound micromechanical investigation of specimens. Three-dimensional discrete element method models of a stacked-ring simple shear test were constructed, in which monotonic and cyclic loadings were applied under constant-volume conditions, and good agreement between the monotonic and cyclic macromechanical behaviors was noted. Micromechanical properties of specimens that were subjected to a cyclic loading are discussed in terms of lateral and intermediate principal stress development, fabric anisotropy, and principal stress rotation. The stress and strain states inside the specimen were investigated and it was shown that despite the uniform stress distribution inside the specimen, the volumetric strain distributes non-uniformly during loading and the non-uniformity grows with cycling, which leads to localized zones of dilative and contractive behavior.

Stress–strain pattern–based criterion to assess cyclic shear resistance of soil from laboratory element tests

The cyclic shear response of soils is commonly examined using undrained (or constant-volume) laboratory element tests conducted using triaxial and direct simple shear (DSS) devices. The cyclic resistance ratio (CRR) from these tests is expressed in terms of the number of cycles of loading to reach unacceptable performance that is defined in terms of the attainment of a certain excess pore-water pressure and (or) strain level. While strain accumulation is generally commensurate with excess pore-water pressure, the definition of unacceptable performance in laboratory tests based purely on cyclic strain criteria is not robust. The shear stiffness is a more fundamental parameter in describing engineering performance than the excess pore-water pressure alone or shear strain alone; so far, no criterion has considered shear stiffness to determine CRR. Data from cyclic DSS tests indicate consistent differences inherent in the patterns between the stress–strain loops at initial and later stages of cyclic loading; instead of relatively “smooth” stress–strain loops in the initial parts of loading, nonsmooth changes in incremental stiffness showing “kinks” are notable in the stress–strain loops at large strains. The point of pattern change in a stress–strain loop provides a meaningful basis to determine the CRR (based on unacceptable performance) in cyclic shear tests.

Plasticity modeling of liquefaction effects under sloping ground and irregular cyclic loading conditions

The formulation of the constitutive model PM4Sand [7] is modified to improve simulations of liquefaction-induced deformations of sloping ground subjected to uniform and irregular cyclic loading. Existing laboratory test data on the response of liquefiable sand under sloping ground conditions subjected to uniform cyclic loading are reviewed and additional experimental data from undrained cyclic direct simple shear (DSS) tests of liquefiable sand under sloping ground conditions subjected to irregular cyclic loading are presented. The previous version of the PM4Sand model (Version 2) and its limitations in modeling liquefaction effects in sloping ground with uniform and irregular cyclic loading are described. Evidence from the laboratory tests show that it is the effect of loading history on the dilation and stiffness characteristics of the response that is not properly captured by Version 2 of the model. The modifications made in Version 3 include a revised dependency of dilation and plastic modulus on the fabric tensor and its history. These modifications are introduced using irregular cyclic DSS test results to illustrate the motivations for the changes in the constitutive equations. Finally, two examples of calibration are presented: one against a specific laboratory test result for a single sand and one against an engineering correlation describing trends observed for many sands across a broader range of relative densities, confining stresses, and loading conditions. The updated formulation in Version 3 of the model is shown to better approximate liquefaction behaviors for sloping ground and irregular cyclic loading conditions.

Monotonic Direct Simple Shear Tests on Sand under Multidirectional Loading

AbstractStress–strain responses of Leighton Buzzard sand are investigated under bidirectional shear. The tests are conducted by using the variable direction dynamic cyclic simple shear (VDDCSS). Soil samples are anisotropically consolidated under a vertical normal stress and horizontal shear stress and then sheared in undrained conditions by applying a horizontal shear stress acting along a different direction from the consolidation shear stress. The influence of the orientation and magnitude of the consolidation shear stress is investigated in this study. There have been only a few previous studies on soil responses under bidirectional shear, of which most studies do not consider the impact of the magnitude of the consolidation shear stress. They are compared with current studies, indicating both similarities and differences. Generally, all test results indicate that a smaller angle between the first and second horizontal shear stress leads to more brittle responses with higher peak strengths, and a larg...

Threshold Shear Strains for Cyclic Degradation and Cyclic Pore Water Pressure Generation in Two Clays

AbstractCyclic threshold shear strains are fundamental cyclic soil properties that have not been fully investigated. To learn more about the threshold shear strains for cyclic degradation, γtd, and cyclic pore water pressure generation, γtp, in fully saturated clays, nine multistage cyclic strain-controlled NGI direct simple shear tests are conducted on laboratory-made kaolinite clay (PI=28) and kaolinite-bentonite clay (PI=55). Three levels of vertical effective consolidation stress, σvc′ (113 kPa, approximately 216 kPa, and approximately 674 kPa); three OCRs (1, 4 and 7.8); and two cyclic loading frequencies, f (0.01 and 0.1 Hz), were applied. In three tests on the normally consolidated (NC) kaolinite clay, γtd varied between 0.012 and 0.014% and γtp between 0.014 and 0.034%. In two tests on the overconsolidated (OC) kaolinite clay with OCR=4, γtd was 0.013% and γtp 0.016 and 0.017%. In two tests on the NC kaolinite-bentonite clay, γtd was 0.013 and 0.016% and γtp 0.052 and 0.078%. In the test on OC kao...

Numerical assessment of cargo liquefaction potential

Liquefaction of fine particle cargoes, resulting in cargo shift and loss of stability of ships, has caused the loss of many lives in marine casualties over the recent past years. Since the dangers of cargo liquefaction have long been known to the shipping industry, the question of why the phenomenon is resurfacing now would be a legitimate one. With this in mind, an UBC3D-PLM model based on FEM theory in the commercial software PLAXIS is presented in this paper as a means to consider soil DSS (Direct Simple Shear) test to verify the model and a method is presented to assess cargo liquefaction potential. Shaking table tests with different amplitude, frequency and initial degree of saturation of cargoes are studied to predict time-domain characteristics. The proposed method could be used as a reference in support of a suitable regulatory framework to address liquefaction and its effect on ship stability.

Cyclic resistance and liquefaction behavior of silt and sandy silt soils

The liquefaction behavior and cyclic resistance ratio (CRR) of reconstituted samples of non-plastic silt and sandy silts with 50% and 75% silt content are examined using constant-volume cyclic and monotonic ring shear tests along with bender element shear wave velocity (Vs) measurements. Liquefaction occurred at excess pore water pressure ratios (ru) between 0.6 and 0.7 associated with cumulative cyclic shear strains (γ) of 4% to 7%, after which cyclic liquefaction ensued with very large shear strains and excess pore water pressure ratio (ru>0.8). The cyclic ring shear tests demonstrate that cyclic resistance ratio of silt and sandy silts decreases with increasing void ratio, or with decreasing silt content at a certain void ratio. The results also show good agreement with those from cyclic direct simple shear tests on silts and sandy silts. A unique correlation is developed for estimating CRR of silts and sandy silts (with more than 50% silt content) from stress-normalized shear wave velocity measurements (Vs1) with negligible effect of silt content. The results indicate that the existing CRR–Vs1 correlations would underestimate the liquefaction resistance of silts and sandy silt soils.

Fundamental investigation of constant stress simple shear test using DEM

The discrete element method (DEM) is employed to explore the responses of three major versions of direct simple shear (DSS) apparatus, i.e., stacked-ring, Cambridge, and NGI types, during shearing. In this regard, results of a stacked-ring simple shear test on glass bead specimens are employed to validate the 3D-DEM model parameters. It is shown that different boundary conditions do not influence internal responses of the specimens, significantly. The uncertainties associated with the behavior of DSS specimens, such as stress and strain non-uniformity, principal stress and strain rotations, the orientation of the failure surface, anisotropy, and non-coaxiality, are investigated. Suggestions are presented to interpret the DSS test results and estimate the stress state inside the specimen during shearing using conventional boundary measurements in the laboratory testing.

Sand-Nonwoven geotextile interfaces shear strength by direct shear and simple shear tests

Soil-reinforcement interaction mechanism is an important issue in the design of geosynthetic reinforced soil structures. This mechanism depends on the soil properties, reinforcement characteristics and interaction between these two elements (soil and reinforcement). In this work the shear strength of sand/geotextile interfaces were characterized through direct and simple shear tests. The direct shear tests were performed on a conventional direct shear device and on a large scale direct shear apparatus. Unreinforced sand and one layer reinforced sand specimens were characterized trough simple shear tests. The interfaces shear strength achieved with the large scale direct shear device were slightly larger than those obtained with the conventional direct shear apparatus. Notwithstanding the differences between the shear strength characterization through simple shear and direct shear tests, it was concluded that the shear strength of one layer reinforced sand is similar to the sand/geotextile interface direct shear strength.

Radial Strain Behaviors and Stress State Interpretation of Soil Under Direct Simple Shear

Abstract Radial strain behaviors and stress state interpretation methods of silica sand consolidated at different K0 values under modified direct simple shear were investigated in this research. Consolidated drained triaxial compression test, direct shear box test, and wire reinforced direct simple shear tests were conducted and the test results were compared and linked with the modified direct simple shear tests. Based on the observed testing data, simple shear specimens with constant lateral stress exhibited relative small radial strain during shear, especially under small shear strains. After the peak shear resistance has mobilized, radial strain increased rigorously until the specimen failed. Confining pressure and K0 values were found to have great deal of influence on the simple shear radial change. Two different methods were adopted to interpret the stress conditions within the simple shear specimen and the “pure shear” method was found more appropriate in interpreting the stress state in the modified direct simple shear test.

Strain-Controlled Cyclic Simple Shear Tests on Sand with Radial Strain Measurements

AbstractStrain-controlled cyclic simple-shear tests were performed on silica sand with radial strain measurements. The specimens were tested under a constant K0 condition and subjected to cyclic loading and postcyclic monotonic loading. Threshold cyclic shear strain, volumetric strain, secant shear modulus, and damping ratio are investigated. Generally, the volumetric strain behavior in this study agreed well with literature findings that were investigated using the conventional cyclic direct simple shear test (without radial constraints). Radial strain during monotonic simple shear (postcyclic loading) was found to be a good parameter in monitoring the onset of flow slide in cohesionless soil. The concept of threshold cyclic shear strain, γt, was adequately applied in assessing the specimen volume change. Dynamic engineering properties, including equivalent shear modulus and damping ratio, were also studied. The damping ratio was found to decrease when the cyclic shear strain amplitude was greater than 2...

Comparative Study of Stress-Strain Characteristic of Peat Soil

This paper shows the stress-strain behavior of peat from the perspective of geotechnical engineering based on laboratory test. Stress happens when a load applied to a certain specimen and deformed the specimen while strain is the response from applied stress on a specimen. Peat is known as an ultimate soft soil in engineering terms because it has low shear strength and compressibility. This research is concerned about the stress-strain behavior of hemic peat. The undisturbed samples were collected at Parit Sulong and Parit Nipah, Batu Pahat, Johore, Malaysia. Normal stresses are 12.5kPa, 25kPa, 50kPa and 100kPa. The shear rate to determine the stress-strain on peat is 0.1mm/min. It is a drained condition test. Both results from each method that obtained were compared based on the relationships of stress-strain. Parit Sulong has higher stress-strain than Parit Nipah. If shear stress increased, shear strain also increased. The result shows that, direct simple shear test of stress-strain that tested on hemic is more relevant than a direct shear box because DSS shear the entire specimen of peat while DSB only shear at the center of the specimen. Geotechnical engineers can use the direct simple shear method to understand efficiently about the stress-strain behaviour of peat.

From Direct Simple Shear Test to Soil Model Development and Supported Excavation Simulation: Integrated Computational-Experimental Soil Behavior Characterization Framework

AbstractA constitutive model that represents soil behavior under a wide range of loading conditions is necessary for the simulation of complex boundary value problems. However, most laboratory tests are interpreted with an assumption of uniform stresses and strains within the tested soil specimen even when the specimen is known to experience nonuniform stress-strain distribution as in the direct simple shear (DSS) test. Numerous tests are often needed to fully characterize a soil’s nonlinear and anisotropic behavior and to develop an appropriate soil model. This paper utilizes an evolutionary inverse analysis approach to extract nonuniform stresses and strains within K0 consolidated-undrained direct simple shear (CK0UDSS) test specimens on Boston blue clay (BBC) and directly develop soil constitutive models. The extracted soil behavior is consistent with known behavior of BBC including anisotropic stress-strain response and small strain nonlinearity obtained under complex laboratory loading conditions. Th...

Cyclic DSS tests for the evaluation of stress densification effects in liquefaction assessment

To evaluate the stress correction factor for the Cyclic Resistance Ratio (“CRR”) under cyclic loading with principal stress rotation, 86 Cyclic Direct Simple Shear (CDSS) tests were performed on two sands, one from Ain Beniam, in Alger, Algeria, and another from Coimbra, Portugal. These sands have distinctive grain shapes and size distributions and were tested with various relative densities and under different initial effective confining stresses. The results of the tests performed with zero initial static shear stress – therefore with the static shear stress factor Kα equal to one – indicate that the values of confining stress level correction factor, Kσ, as currently recommended, seem to underestimate the cyclic resistance.