Direct Simple Shear Tests on Specimens with Thick Rings

Stress can produce a deformation because real material is not rigid, the deformation will measure the strain. Stress-strain is important in determining peat behaviour. Peat cannot support too much load on it because of peat have very low strength, high compressibility and long-term settlement. The objective of this study is to determine the behaviour of stress-strain characteristic using different test. The undisturbed samples were collected at Parit Nipah, Batu Pahat, Johore, Malaysia. The tests are direct simple shear and direct shear box. These methods cover the determination of the stress-strain relationship of peat and to investigate the behaviour of peat. Normal stresses are 12.5, 25, 50 and 100 kPa with 0.1 mm/min rate of shear. This study is to know the stress-strain between direct simple shear test and direct shear test based on peat specimens of hemic. The test results will contribute and establish the drained shear characteristic of testing peat. It shows that direct simple shear test stress-strain is increasing clearly than direct shear test. Besides that, direct simple shear is suitable to use on peat soil rather than direct shear box. This research can help the geotechnical engineers and can be used in the development of foundation and as well as constructions.

Chiang Mai province is located in northern part of Thailand, wherein low to medium earthquake can occur. Therefore, this research aims to present an assessment of dynamic properties of Chiang Mai sand using cyclic direct simple shear test. Two of the most important parameters of dynamic properties in any dynamic analysis related to soils are shear modulus and damping ratio. The monotonic direct simple shear apparatus, which is developed at Norwegian Geotechnical Institute by Bjerrum and Landva, is modified to cyclic direct simple shear so as to be able to determine dynamic properties of Chiang Mai sand. Drained (constant normal stress) tests are carried out with saturated sand sample reconstituted by water pluviation method, which can closely replicate the in-situ fabric of natural sand deposits. In this study, relative density, vertical stresses, shear strain amplitude, and frequency are varied to observe their effect on sand dynamic properties. It can be concluded from the testing results that shear modulus and damping values mainly depend on vertical stress and shear strain. Shear modulus decreases with increasing shear strain amplitude. Oppositely, it increases with increasing vertical stress. The value of hysteretic damping increases with increasing shear strain amplitude. In contrast, when damping ratio decreases with increasing values of vertical stress. The experimental results of present study compared with previous investigations are found to be in fair agreement. All in all, this research is the first work focused on dynamic properties of Chiang Mai sand, which gives great distribution to the calculation of ground response during an earthquake. It also facilitates the following researchers who want to conduct further research on advanced soil laboratory testing about cyclic soil response in Chiang Mai as well as in Thailand

DEM simulations on the influence of carbonate precipitation on liquefaction mitigation of sand

The cyclic resistance of sand unit 3c at Duncan Dam in British Columbia for overburden stresses of about 2 to 12 atm (1 atm = 101.325 kPa) was evaluated previously using cyclic undrained direct simple shear (DSS) and cyclic undrained triaxial testing of samples obtained using frozen sampling techniques. The in situ standard penetration test (SPT) and laboratory testing results provide a unique set of data for evaluating how the effects of effective overburden stress are accounted for in liquefaction evaluation procedures. The present study re-examines the cyclic resistance of these sands based on the field and laboratory test data for the unit 3c sands underlying Duncan Dam relative to the site-specific procedures developed by Pillai and Byrne and the liquefaction triggering evaluation procedures presented by Idriss and Boulanger, Youd et al., and Cetin et al. The differences in the results and the reasons for the differences are discussed.

The Direct Simple Shear (DSS) test devices have a major fundamental defect which has been recognized for over 40 years. In this paper, the limitations of the DSS test are emphasized by test results obtained on a highly sensitive and brittle clay of Eastern Canada. The DSS devices are no real improvement over the direct shear devices and the value of the triaxial test is far superior.

The factors and mechanisms controlling the accumulation of shear strains of clean uniform sands exhibiting cyclic mobility behavior under level-ground conditions are examined. This phenomenon is investigated through a series of constant-volume cyclic direct simple shear (DSS) tests subjected to uniform and irregular loading conditions, and undrained cyclic element tests collected from the literature. Experimental data show that the rate of shear strain accumulation per loading cycle depends on the relative density, cyclic stress amplitude, and effective overburden stress. Mechanisms of shear strain accumulation are investigated by decoupling the shear strain developed in each loading cycle in two components: γ0, developed at near-zero effective stress, and γd, developed during dilation. Results show that γ0 mostly depends on the shear strain history, while γd depends on the cyclic stress amplitude and relative density. These dependencies of γd and γ0 are used to provide an explanation for the gradual decrease of the rate of shear strain accumulation that is observed while increasing the number of post-triggering loading cycles in tests performed on dense specimens.

An elasto‐plastic constitutive model is proposed to account for the effect of principal stress rotation that commonly occurs and significantly influences soil behavior. The model is based on a concept of adding plastic strain increments obtained from two mobilized planes: a plane of maximum shear stress which swings as the principal stress rotates, and a horizontal plane which is spatially fixed. Models based on the plane of maximum shear stress alone are particularly sensitive to horizontal effective stress ratioK0(=σ′x/σ′y), whereas the proposed model gives a similar skeleton behavior for soils at the same density and mean effective stress, regardless of the value ofK0, as observed in laboratory tests. The model is firstly calibrated by data from drained and undrained monotonic and cyclic Direct Simple Shear (DSS) tests onK0‐consolidated specimens of Nakdong River sand in loose and dense states. The capability of the proposed model in modeling of the conventional liquefaction effects: initial shear stress conditionα(=τ′xy/σ′y) withKαcorrections, and initial confining stress conditionσ´ywithKσcorrections, is also emphasized in this paper.

Laboratory assessment of the effect of vibro-replacement ground improvement on the mechanical response of natural silt

Monotonic and post cyclic behavior of sands under different strain paths in direct simple shear tests

Dynamic analyses of steel catenary risers (SCRs) suspended from a floating platform usually show that the vicinity of the zone where the riser touches down on the seabed is important to fatigue assessments, and can be critical in realizing an economical SCR design or in assessing SCR design life extension. The motivations of the paper are to advance the understanding of the complex mechanism of SCR-soil interactions in a comprehensive yet efficient way, to supplement the extensive model test-based SCR-soil interaction studies in the literature, and to offer a numerical tool to predict the SCR-soil interaction in different clay types. The objective is to investigate the fundamental mechanism of SCR-soil interactions using advanced finite element (FE) analyses. The FE analysis is conducted in Abaqus using the coupled Euler-Lagrangian (CEL) technique to capture the local large deformation surrounding a riser. A strain-softening soil model for deepwater soft clays subject to cyclic degradation is developed based on cyclic direct simple shear (DSS) tests to avoid cycle-by-cycle simulations. The stress-displacement relations are proposed in the FE analysis to avoid the size effect associated with strain-softening soils. The FE analysis results are compared to the test data from the independently conducted model tests and the established results from the literature. Good agreements among different studies are observed.

This study presents cyclic resistances of an instrumented medium dense sand (i.e., the Sand Array) and medium plastic silt (i.e., the Silt Array) deposit deduced from in situ dynamic testing using the controlled blasting test method. Particle velocity records were used to calculate the cyclic resistance ratios, CRRs, and convert the transient blast-induced ground motions into their equivalent number of shear stress cycles, Neq, through consideration of the cyclic resistance observed from stress-controlled, constant–volume, cyclic direct simple shear (DSS) tests. The CRR-Neq relationship developed for the medium dense sand deposit demonstrated that the in situ cyclic resistance is larger than that (1) expected from cyclic DSS test specimens reconstituted to the in situ vertical effective stress, relative density, and shear wave velocity, Vs; and (2) calculated using case history-based, penetration-, and Vs-based deterministic formulations of liquefaction triggering models. Differences between the in situ cyclic resistance and that computed using probabilistic liquefaction triggering models reduced somewhat when considering probabilities of liquefaction exceeding 50% and 85%, depending on the model. Partial drainage during dynamic loading of the Sand Array appears to have contributed to the cyclic resistance of the sand deposit, with an increase of 6% to 27% compared to that estimated for fully undrained conditions. Differences between the cyclic failure criteria used to interpret the cyclic resistance of intact laboratory specimens of silt result in significantly different interpretations of the in situ CRR; the use of maximum excess pore pressure-consistent criteria appears to provide the best representation of the in situ, stress-based cyclic resistance when high quality, intact silt specimens form the basis for conversion of transient seismic waveforms to uniform shear stress loading cycles. The investigation described herein suggests that the reduction of cyclic resistance for plastic soils to account for multidirectional shaking ranges from 0% to 7% over Neq of 1 to 100.

Seismic response of geostructures in liquefiable soils is often quite complex and may involve several factors that contribute to the key mechanisms affecting the overall performance. However, in some cases, if critical mechanisms are well understood, it might be possible to estimate the system response by using relatively simple analytical tools. This study investigates the potential use of direct simple shear (DSS) test in estimating the seismic response of sheet-pile retaining structures supporting liquefiable soils. Through a comprehensive analysis of the centrifuge experiments carried out as part of the 2022 Liquefaction Experiments and Analysis Projects (LEAP-2022), coupled with Type-C numerical simulations of the centrifuge experiments, it is observed that the sheet-pile wall response is critically related to the stress-strain response of the soil near the tip of the sheet-pile wall which is embedded in a dense layer of Ottawa F65 sand. An in-depth understanding of such stress-strain response using laboratory-based element tests might provide a means to estimate the wall rotation and its lateral displacements. To this end, simplified numerical analyses were performed to estimate the initial vertical effective stress and time-history of shear stresses caused by the earthquake near the tip of the sheet-pile wall. Then, several specimens of Ottawa F65 sand were prepared at relative densities comparable to the values achieved in the LEAP-2022 centrifuge experiments and were subjected to the estimated shear stress time-histories. By assuming a rigid body motion of the sheet-pile wall during earthquake, the rotation of the wall at the end of earthquake motion was then estimated using the permanent shear strains measured in the DSS tests. It is observed that the estimated rotations of the sheet-pile wall compare well with the rotations observed in the centrifuge tests and those obtained in Type-C numerical simulations. In these cases, DSS tests are shown to provide a relatively simple means for estimating the rotations of the sheet-pile wall.

This study evaluated the cyclic response and re-consolidation volumetric strain (εV) of clean sand subjected to repeated earthquakes at non-fully liquefied stage. A series of repeated cyclic direct simple shear tests (CDSS) at various cyclic stress ratios (CSR) and followed re-consolidation phases were performed on loose sand. From the experimental results, CSR, number of applied shear event, shear strain induced by shaking event were factors influencing the cyclic behavior and εV. For non-liquefied samples subjected to repeated shear events, two concepts of maximum double amplitude shear strain (γDAmax) and evolution of double amplitude shear strain (ΔγEDA) in relation to εV were examined, in which (ΔγEDA − εV) concept exhibited a better correlation and was suggested as an alternative approach for examining the dynamic response during shaking events induced by earthquakes.KeywordsLiquefactionVolumetric strainCyclic shear strainRepeated earthquake

Stress-strain behavior of Ottawa sand in cyclic direct simple shear and modeling of cyclic strength using Artificial Neural Networks

ABSTRACTMost of the robust artificial intelligence (AI)‐based constitutive models are developed with synthetic datasets generated from traditional constitutive models. Therefore, they fundamentally rely on the traditional constitutive models rather than laboratory test results. Also, their potential use within geotechnical engineering communities is limited due to the unavailability of datasets along with the model code files. In this study, the data‐driven constitutive models are developed using only laboratory test databases and deep learning (DL) techniques. The laboratory database was prepared by conducting cyclic direct simple shear (CDSS) tests on reconstituted sand, that is, PDX sand. The stacked long short‐term memory (LSTM) network and its variants are considered for developing the predictive models of the shear strain (γ [%]) and excess pore pressure ratio (ru) time histories. The suitable input parameters (IPs) are selected based on the physics behind the generation of ru and γ (%) of the liquefiable sands. The predicted responses of γ (%) and ru agree well in most cases and are used to predict the dynamic soil properties of the PDX sand. The same modeling framework is extended for other sand and compared with existing AI‐based constitutive models to verify its practical applicability. In summary, it is observed that though the trained models predicted the time histories of ru and γ reasonably well; however, they struggled to predict the hysteresis loops at higher cycles. Therefore, more research is needed to verify and enhance the predictability of existing AI‐based models in the future before using them in practice for simulating cyclic response.