Simple Shear Tests Research Articles

Sand liquefaction in simple shear tests

Liquefaction is a phenomenon marked by a rapid loss of soil strength and stiffness, which generally occurs in loose saturated sandy deposit during earthquake because of the generation of excess pore water pressure. Several experimental researches concluded that liquefied soil behaves as a fluid during ground movement, but after the earthquake motion ceases, due to the dissipation of excess pore water pressure, the liquefied soil recovers its initial stiffness and returns to behave as a solid. Liquefaction resistance of sandy soil can be studied by means of Cyclic Simple Shear (CSS) test or Cyclic Triaxial (CTX) tests. While CTX tests are widely used in liquefaction studies due to their simplicity, CSS tests are more representative of stress conditions produced during an earthquake by simulating the continuous rotation of the principal stress axes. In this research the preliminary results of CSS tests carried out with confining rings on the sandy samples retrieved in the South of Sicily are reported. The apparatus is described in detail. All samples used were obtained from the same type of Italian sand by using same preparation method to minimize the number of factors influencing the results. Moreover, all tests were conducted by a single operator. All experimental results are reported in the plane cyclic resistance ratio (CRR) and number of cycles where liquefaction occurs (Nliq) in order to assess the liquefaction phenomenon.

Evaluation of the Effects of Different Strain Paths on the Behavior of Sands Using Direct Simple Shear Tests

Abstract Many researchers have evaluated different parameters that can affect the mechanical behavior of sands. However, most of the conducted investigations considered drained and undrained stress–strain paths as the limiting boundaries of the behavior; recently applied studies have indicated that this assumption cannot be accurate for all situations. In this paper, by using expansive and contractive strain paths (in addition to the conventional constant volume path), partially drained responses of sands are simulated. Influences of different grain size distributions on the behavior of sands are studied by controlled coupling between volumetric to shear strain ratios. The results show that the asymptotic stress ratio (steady state stress ratio), phase transformation stress ratio, and instability stress ratio depend on the experienced strain paths and cannot be considered material constant (inherent) parameters. It is shown that coarse sands can be affected by the various strain paths more than finer sands, and loose sands are more sensitive against the partially drained strain paths compared to dense sands.

Linking laboratory quasi-steady state strengths to field scale performance of tailings

Current state of practice for the assessment of liquefied strengths of tailings relies primarily on empirical or semi-empirical correlations based on penetration testing. That is, despite liquefied strength being arguably the most important strength parameter for the design of brittle tailings storage facilities, there is much less success or acceptance of the use of laboratory element tests to support strength selection compared to other forms of strengths inferred in geotechnical engineering. This is particularly the case for tailings at a state near or slightly dense of the critical state line (CSL) for which there is ample evidence of field-scale flow liquefaction but where laboratory element tests often behave in a manner inconsistent with such field-scale response – at least at large strains. The current paper examines the quasi steady state (QSS) strength of sands and tailings for which the CSL has been measured, linking the observed strengths to inferred in situ behaviour through the state parameter. Particular focus is placed on QSS strengths obtained from simple shear tests carried out within a hollow cylinder torsional shear system where the stress state in the test is a better representation of in situ below-slope conditions that the triaxial compression test. In particular, the marked effect of intermediate principal stress on the QSS in sands is highlighted. Alternatively, the negligible anisotropy seen in a sandy silt gold tailings, and the potential implications in the context of QSS strengths and field-scale behaviour, are examined and emphasised.

Fabric-based jamming phase diagram for frictional granular materials.

A jamming phase diagram maps the phase states of granular materials to their intensive properties such as shear stress and density (or packing fraction). We investigate how different phases in a jamming phase diagram of granular materials are related to their fabric structure via three-dimensional discrete element method simulations. Constant-volume quasi-static simple shear tests ensuring uniform shear strain field are conducted on bi-disperse spherical frictional particles. Specimens with different initial solid fractions are sheared until reaching steady state at a large shear strain (200%). The jamming threshold in terms of stress, non-rattler fraction, and coordination numbers (Z's) of different contact networks is discussed. The evolution of fabric anisotropy (F) of each contact network during shearing is also examined. By plotting the fabric data in the F-Z space, a unique critical fabric surface (CFS) becomes apparent across all specimens, irrespective of their initial phase states. Through the correlation of this CFS with fabric signals corresponding to jamming transitions, we introduce a novel jamming phase diagram in the fabric F-Z space, offering a convenient approach to distinguish the various phases of granular materials solely through the direct observation of geometrical arrangements of particles. This jamming phase diagram underscores the importance of the microstructure underlying the conventional jamming phenomenon and introduces a novel standpoint for interpreting the phase transitions of granular materials that have been exposed to processes such as compaction, shearing, and other complex loading histories.

The monotonic behaviour of a low- to medium-density chalk through in-situ and laboratory characterisation

Chalk is a highly variable cemented biomicrite limestone that can show widely different rock strengths and patterns of micro to macro fissuring and jointing, due to variations in depositional environments and local geological histories. This paper describes the characterisation of a very weak to weak, low- to medium-density chalk through in situ profiling and laboratory testing, which provided new insights into the geomaterial’s mechanical behaviour. The chalk de-structures when taken to large strains, leading to remarkably high pore pressures beneath penetrating cones and degraded responses in full-displacement pressuremeter tests. Laboratory tests on carefully formed specimens explored the chalk’s unstable structure and marked time-, rate- and pressure dependency. A clear hierarchy was found between profiles of peak strength with depth from Brazilian tension, drained and undrained triaxial and direct simple shear tests conducted from in-situ stress conditions. Highly instrumented triaxial tests sheared from low confining stresses indicated stiffness anisotropy and showed very brittle failure behaviour from small strains. Progressively more ductile behaviour was seen as confining pressures were raised, with failures being delayed until increasingly large strains and finally stable critical states were attained. The chalk’s mainly sub-vertical jointing and micro-fissuring led to properties depending on specimen scale, with high-quality laboratory stiffness measurements significantly exceeding those obtained from in-situ geophysical testing, which far exceed the operational stiffnesses of the chalk mass. While compressive strength and stiffness appear relatively insensitive to effective stress levels, consolidation to higher pressures closes micro-fissures and reduces anisotropy. The results provided the basis for numerical analysis with advanced constitutive models that inform the interpretation of axial and lateral tests on driven piles and inform the development of new practical design methods.

Effects of initial static shear on liquefaction behaviour of Toyoura sand in undrained multi direction dynamic cyclic simple shear tests and DEM

Effects of initial static shear on liquefaction behaviour of Toyoura sand in undrained multi direction dynamic cyclic simple shear tests and DEM

Characterisation of the behaviour of liquefaction triggering in a cyclic undrained simple shear test setting

Characterisation of the behaviour of liquefaction triggering in a cyclic undrained simple shear test setting

Effect of lateral confinement method on excess pore pressure generation under strain-controlled cyclic direct simple shear test

Effect of lateral confinement method on excess pore pressure generation under strain-controlled cyclic direct simple shear test

SPH implementation of a critical state-based hypoplastic model for granular materials in large-deformation problems

In this work, an advanced hypoplastic model incorporating the critical state is integrated into smoothed particle hydrodynamics (SPH) for numerical investigation of problems with large deformation. This numerical method performs well in cases of element tests such as oedometer test, simple shear test and plain strain compression test, which usually own regular velocity fields. However, the standard SPH implementation will generate significant stress drift away from the failure surface in more complex geotechnical problems featured with dramatically-varying velocity field. This unrealistic stress state may deteriorate the stress state with a further step. As a result, a vicious circle takes place, which could give rise to a calculation failure. With this regard, a return mapping strategy is proposed to regulate the stress state locating beyond the failure surface. To this end, a closed-form solution to predicting the failure surface implicitly incorporated in the hypoplastic model is derived. Finally, the capability of the proposed numerical method is examined with two classical benchmark problems for granular materials, including the sand column collapse and rigid footing by comparing the numerical results with those from experiments and theoretical solutions.

Shear modulus prediction of landfill components using novel machine learners hybridized with forensic-based investigation optimization

The assessment of the shear modulus (G) of municipal solid waste (MSW) and leachate-contaminated soil (LCS) is of vital importance for landfill engineering investigation and achieving sustainable development goals. In this study, 153 cyclic triaxial tests on MSW (reconstructed samples under CU conditions) and 104 cyclic simple shear tests (strain controlled) on LCS were conducted to assess the shear modulus. The examined variables are plastic percentage (0–0.274), age (0–16 years), shear strain (0.075–3.63%), unit weight (9 and 12 KPa), frequency (0.1–1 Hz), and confining pressure (75 and 150 KPa) for MSW and leachate content (0–40%), shear strain (0.05–1%), frequency (0.1 and 1 Hz), and vertical load (50–350 KPa) for LCS. Laboratory assessment of cyclic parameters is costly and complicated which requires precise testing and the experts. Therefore, multiple types of ensemble models (AdaBoost, GBRT, XGBoost, and Random Forest (RF)) were utilized along with Forensic-Based Investigation Optimization (FBIO). The application of numerical and computational approaches as the main novelty of the research can be a step forward to save time and money. The performance comparison of the established models on experimental datasets showed that GBRT- FBIO model outperformed the other models for G-MSW (R2 =0.99, RMSE=0.164, MAE=0.122, MAPE=0.073, and a20-index=0.956 for testing datasets) and G-LCS (R2 =0.99, RMSE=0.477, MAE=0.385, MAPE=0.028, and a20-index=1 for testing datasets). Finally, the outcomes of the sensitivity analysis also displayed the most participation of shear strain (50.87%) and vertical load (52.1%) to the shear modulus of MSW and LCS.

Sample size effects on the critical state shear strength of granular materials with varied gradation and the role of column-like local structures

Assessing the shear strength of coarse granular soils is challenging because testing devices in the laboratory often limit the maximum particle size (dmax). Although engineering standards define representative elementary volumes (REVs) using the aspect ratio α = X/dmax, where X is the characteristic sample size, they often disagree on the minimum α, as the effects of sample scale on shear strength are still not well understood. This paper presents a discrete-element study on the combined effect of specimen size and grading on the critical state shear strength of granular materials. The study covers a wide range of aspect ratios and demonstrates that the macroscopic response is stable for α ≥ 15 – which is significantly higher than the standard requirement of α ≥ 10 for simple shear tests. The granular microstructure is also strongly affected by α and the formation of column-like structures of grains carrying strong contact forces, reaching sample size independent conditions only for α ≥ 20. Such column-like structures are shown to be primarily composed of the largest classes of grains, supporting the fact that grading has no effect on the critical state shear strength and dmax correctly serves to scale a granular sample to the size of the testing device.

Small-strain, non-linear elastic Winkler models for uniaxial loading of suction caisson foundations

Soils exhibit non-linear stress–strain behaviour, even at relatively low strain levels. Existing Winkler models for suction caisson foundations cannot capture this small-strain, non-linear soil behaviour. To address this issue, this paper describes a new non-linear elastic Winkler model for the uniaxial loading of suction caissons. The soil reaction curves employed in the model are formulated as scaled versions of the soil response as observed in standard laboratory tests (e.g. triaxial or simple shear tests). The scaling relationships needed to map the observed soil-element behaviour onto the soil reaction curves employed in the Winkler model are determined from an extensive numerical study employing three-dimensional finite-element analysis. Key features of the proposed Winkler model include: computational efficiency, wide applicability (it can be used for caisson design in clay, silt or sand) and design convenience (the required soil reaction curves can be determined straightforwardly from standard laboratory test results). The proposed model is suitable for small and intermediate caisson displacements (corresponding to fatigue and serviceability limit state conditions) but it is not applicable to ultimate limit state analyses.

Reaching Large Strains During Simple Shear Experiments Thanks to Sequential Re-Machining of the Free Edges

BackgroundThe simple shear experiment is widely used for the calibration of plasticity models due to straightforward post processing. The specimen can be as simple as a rectangular strip of sheet metal, but the maximum strain is limited by early initiation of fractures from the free edges. Avoiding this drawback has been a major motivation for the development of new specimens with optimized edge geometries or the in-plane torsion test, but at the cost of a more complex analysis of the test and often a reduction of the gauge section.ObjectiveThe objective of the present work is to overcome the initiation of fracture from the free edges during simple shear experiments. Our goal is to double the achievable maximum strain, while keeping the size of the specimen and the post processing simplicity of a standard simple shear test.MethodsA sequential single shear test is proposed, consisting of several two steps sequences on a notched geometry. First, an interrupted shear test is performed up to a specified displacement value. Then, the damaged free edges of the specimen are removed through milling. The specimen is then ready for the following sequence of shear and re-machining.ResultsExperiments are performed on three engineering materials, with up to five loading-machining sequences. The maximum attained effective strain is up to two times the one reached during a monotonic experiment. Numerical simulations are used to validate the shear stress and strain calculations from experimental measurements. Practical recommendations are derived for the choice of the displacement step size and Digital Image Correlation analysis.ConclusionIt is found that the maximum strain attained before the undesired failure of the specimen during simple shear test can be substantially extended through repeated re-machining of the specimen boundaries, enabling behavior identification at larger strains.

Dilatancy Equation Based on the Property-Dependent Plastic Potential Theory for Geomaterials

The dilatancy equation ignores the noncoaxiality of granular soil for the coaxial assumption of the direction of the stress and strain rate in conventional plastic potential theory, which is inconsistent with extensive laboratory tests. To reasonably describe the noncoaxial effects on dilatancy, the energy dissipation of plastic flow is derived based on the property-dependent plastic potential theory for geomaterials and integrates the noncoaxiality, the potential theory links the plastic strain of granular materials with its fabric, and the noncoaxiality is naturally related to the mesoscopic properties of materials. When the fabric is isotropic, the dilatancy equation degenerates into the form of the critical state theory, and when the fabric is anisotropic, it naturally describes the effects of noncoaxiality. In the plane stress state, a comparison between a simple shear test and prediction of the dilatancy equation shows that the equation can reasonably describe the effect of noncoaxiality on dilatancy with the introduction of microscopic fabric parameters, and its physical significance is clear. This paper can provide a reference for the theoretical description of the macro and micro mechanical properties of geomaterials.

Seismic performance of a sheet-pile retaining structure in liquefiable soils: Numerical simulations of LEAP-2022 centrifuge tests

This paper focuses on the numerical simulations of a sheet-pile retaining structure under liquefaction-induced lateral spreading, using data from LEAP-2022 dynamic centrifuge tests conducted at various facilities. The simulations employ an updated pressure-dependent multi-yield surface constitutive model (i.e., OpenSees PDMY03), incorporating dilatancy, cyclic mobility, and associated shear deformation features. To more accurately represent the liquefaction resistance characteristics of medium to dense Ottawa sands during LEAP-2022, the contractive and dilative rules of the PDMY03 model are updated based on experimental observations. Subsequently, the model parameters are calibrated through a series of stress-controlled cyclic direct simple shear (CDSS) tests to closely match the liquefaction strength curves of Ottawa sand. With these calibrated model parameters, dynamic response analyses of the sheet-pile retaining structure in liquefiable soils are performed, and the computed results are directly compared to the centrifuge experimental data. It is demonstrated that the updated PDMY03 constitutive model, combined with the employed computational framework, has the potential to realistically predict the experimental results of the sheet-pile retaining structure subjected to liquefaction-induced lateral spreading. Overall, this comprehensive approach enables a realistic evaluation of the performance of equivalent sheet-pile retaining structures under conditions of seismically-induced liquefaction, as well as other relevant scenarios.

Discrete Element Simple Shear Test Considering Particle Shape

The particle shape has significant effects on the slip and rotation of particles in the shear of geomaterials, which is an important factor in the deformation and strength of geomaterials. This paper employed particle flow code (PFC3D) to simulate the simple shear test, and ellipsoidal particles with different aspect ratios were prepared to study the effects of particle shape on the mechanical behavior and fabric evolution of granular materials under complex stress paths. The numerical results show that the particle shape has a significant effect on the peak strength, dilatancy, non-coaxiality, and other mechanical properties of granular materials. The contact fabric evolves from orthotropy to transverse isotropy under the principal stress axes rotation. This paper will provide a reference for natural granular materials with different shapes in the study of mechanical behavior and the micro-constitutive model.

Dynamic response of a low plasticity silt deposit: comparison of in-situ and laboratory responses

This study compares the in-situ dynamic response of a low plasticity silt deposit subjected to multidirectional loading from vibroseis shaking and controlled blasting to a suite of element-scale, cyclic laboratory test specimens. The agreement between excess pore pressures and simple shear strain relationships over a wide range in strains is remarkable. Slightly larger excess pore pressures observed in-situ are attributed to three-dimensional loading and pore pressure migration/redistribution in the shallower portions of the deposit. Noted differences in shear modulus, G, are attributed to strain rate effects, spatial variability in the in-situ stiffness, and hydraulic boundary conditions. The variation in in-situ G/Gmax follows the trend from torsional shear specimens up to 0.4% shear strain; larger strains in the silt deposit imposed by controlled blasting yielded a stiffer response than that from cyclic torsional shear and direct simple shear specimens due in part to field drainage for deeper portions of the deposit. The in-situ cyclic resistance ratio for the deeper portion of the deposit in which plane body waves could be assumed and for the selected excess pore pressure ratio criterion was larger than that of stress-controlled cyclic direct simple shear (CDSS) test specimens, despite the detrimental effect of multidirectional shaking in the field. The effect of strain history, spatial variability, and drainage boundary conditions to drive differences between the in-situ and laboratory test specimens is identified.

Experimental study of the effects of initial shear stress on post-liquefaction behavior of submarine liquefiable ground: An energy-based evaluation

In offshore earthquake regions, granular soils are prone to liquefaction and flow failure, resulting in imponderable damage to adjacent structures. When the foundation is constructed on inclined terrains, initial static shear stress induced by the self-weight of slope soils can significantly affect the soil behavior and liquefaction potential. This paper discusses the effects of initial shear stress on the liquefaction and post-liquefaction behavior through an energy-based approach. A series of monotonic and cyclic undrained simple shear tests are performed under various initial shear stress levels. The cumulative dissipated energy is used to evaluate the effects of initial shear stress on typical soil behaviors, including the onset of instability in monotonic tests and the liquefaction in cyclic tests. In monotonic tests, the cumulative energy required for triggering instability decreases with the initial shear stress level at the post-liquefaction stage. Moreover, at the same relative density, a strain-softening response on virgin samples can be transformed into a strain-hardening type at the post-liquefaction stage. In cyclic tests, a unique correlation is found between cumulative energy and pore water pressure and it is closely related to the initial shear stress level. Based on the test results, two relationships are proposed to estimate the cumulative energy required for liquefaction or flow-type failure at the initial liquefaction and post-liquefaction stages.

Influence of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands

Abstract This technical article presents the influence of sample quality on the compressibility parameters and undrained shear strength (c u) of soft soils from the Vistula Marshlands. The analysis covers: (1) quality of soft soil according to three criteria: void ratio (Δe/e 0 index), volumetric strain (Δɛ v) and C r/C c ratio; (2) influence of storage time on quality; (3) influence of sample quality on undrained shear strength (c u), and (4) reliability of compression and undrained shear strength parameters estimation. The sample quality of three different soft soils (peat, organic clays, and organic silts) was investigated using dataset of geotechnical investigations from the Vistula Marshlands. The reliability of oedometer tests and compressibility parameters determination was shown. Different undrained shear strength estimates (from lab and field tests) were juxtaposed with sample quality. In situ estimates of undrained shear strength were compared with results of triaxial tests and direct simple shear test on reconstituted samples as well as SHANSEP estimates. The results of research are grouped in seven lessons. The most important outcomes are: (1) the quality of samples is at best moderate or poor and there is no significant influence of storage time on sample quality, (2) regardless of testing method, the undrained shear strength natural variability of the Vistula Marshlands soft soils is between 20% and 50% depending on deposit depth and soil type, (3) the most accurate estimation of undrained shear strength can be obtained from field vane test (FVT) while unconsolidated, undrained compression (UUC) triaxial tests should be avoided, (4) SHANSEP approach can be considered as a valuable estimate of c u (next to the FVTs), which additionally allows in relatively easy way to establish lower and upper bounds of c u.

Characteristics of MICP- and EICP-treated sands in simple shear conditions: a benchmarking with the critical state of untreated sand

Microbial- or enzyme-induced calcium carbonate (CaCO3) precipitation (MICP and EICP) are relatively new ground improvement techniques. In this study, the mechanical behaviour of biotreated (MICP/EICP) and untreated sands was investigated in light of the critical state soil mechanics framework using a series of direct simple shear (DSS) tests. A wide range of calcium carbonate content (CC), initial void ratio after consolidation (e0) and effective initial normal stress ([Formula: see text]) was considered. The biotreated specimens showed improved shear strength and dilative tendency compared to untreated specimens with similar initial states. The ultimate state (US) for the biotreated sand shifted towards a smaller void ratio (e) than the value of e at the critical state of untreated sand at the same σ′N in e–log σ′N space. Compared to untreated sand, a significantly larger US stress ratio was achieved for the biotreated sand, particularly at high CC and low [Formula: see text]. The characteristic features of undrained behaviour, such as instability stress ratio, stress ratio at phase transformation and flow potential showed good relationships with modified initial state parameter, void ratio after biotreatment and CC. The bonding ratio, (τ/σ′N)bond, was used to quantify the interparticle bonding. The peak value of (τ/σ′N)bond for the biotreated sand was significantly larger than zero, particularly at high CC and low [Formula: see text], while the peak (τ/σ′N)bond for the untreated sand was negligible. It was also observed that the mobilisation and degradation of calcium carbonate bonds in biotreated sand during DSS shearing are influenced by both CC and [Formula: see text].