Undrained Cyclic Triaxial Tests Research Articles

Experimental and numerical investigation on the load stability of coal cargoes during marine transport

During marine transport of coal commodities, cargo slip or liquefaction failure scenarios within the hold may occur under cyclic ship motions. The resulting cargo shift affects the vessel stability, and subsequently endangers goods and crews on board the vessel. This study aims to investigate the coal cargo stability under marine transport conditions. A suite of six coal samples was selected to undertake a series of undrained cyclic triaxial tests to investigate their liquefaction resistance. Results were subsequently compared to the liquefaction threshold advised by International Maritime Organisation. It was suggested that finer coals were observed to be more susceptible to liquefaction. In addition, discrete element modelling of the coal cargoes was conducted to study the cargo slip susceptibility. Calibration was performed to ensure materials modelled in the numerical program reflected the physical behaviours. Results indicated coarser coal samples with lower moisture contents exhibited cargo slip failures under nominated rolling ship motion. Nevertheless, resulting centre of gravity shift from cargo slip exhibited negligible effect on the cargo stability. Outcomes of this study provided important safety guidelines on marine transportation of coal commodities.

Experimental assessment of the small-strain response of residual soil under monotonic and cyclic loading

Residual soil from the Passo Fundo region (Brazil), presents natural cementation, responsible for a peculiar behaviour that is clearly distinguishable from that of soils with other origins. Understanding this behaviour and the effects of the fabric, with an influence on the cementation bonding, is essential to characterise these materials. Therefore, the aim of the present study is the mechanical characterisation of this soil, mainly by analysis and testing of remoulded and undisturbed samples. The experimental programme included uniaxial compressive strength tests, oedometer tests, consolidated drained monotonic triaxial tests and consolidated undrained cyclic triaxial tests. Based on the data collected, a clear influence of interparticle bonding, provided by the natural cementation, was detected on the soil's intrinsic behaviour; the undisturbed material showed a higher stiffness modulus than the remoulded material, mainly due to the bond breakage to which the latter was submitted, losing its natural cementation. A uniaxial confining stress of 89.4 kPa was obtained for the undisturbed material, assumed to be its yield stress. This value was corroborated by the oedometric (87.5 kPa), isotropic (80 kPa) and triaxial compression (90 kPa). The natural cementation was influential in every type of loading and should be considered during the design process.

A new effective stress method for nonlinear site response analyses

AbstractA generic loosely coupled effective stress method is presented in this article for one‐, two‐ and three‐ dimensional (1D, 2D and 3D) nonlinear site response analyses. In this method, the 1D non‐Masing hysteretic constitutive model of Chen et al (2020) is extended into 2D and 3D stress conditions, by presenting a clever generalized formulation of equivalent shear strain (γeq). The element‐level simulation tests show that the proposed algorithm of γeq is conceptually simple with high precision to capture the strain reversals under complex multidirectional shakings. The coupling between the cyclic stiffness degradation and the excess pore water pressure (EPWP) generation during irregular cyclic loadings is established using the proposed algorithm of γeq in conjunction with the Chen et al (2019a) EPWP generation model and the extended non‐Masing hysteretic constitutive model. The simulations of the undrained cyclic triaxial tests using the new effective stress method reproduce excellently the observed response of the saturated sand specimens, demonstrating the ability to represent the undrained behavior of liquefiable sands during uniform cyclic loadings. The new effective stress method is then used to simulate the response of a downhole array liquefied site in Japan, which shows an excellent agreement between the simulations and the recordings in both horizontal and vertical components of ground motions at different depths.

Laboratory-based assessment on similarities between dynamic behavior of MSW and clay

The dynamic response of landfills under seismic loads is greatly dependent on stress–strain cyclic characteristics of municipal solid waste (MSW). Accurate evaluation of these characteristics is essential for improving the current understanding of MSW’s seismic behavior and, consequently, stabilizing landfills under such loads. Therefore, a comprehensive undrained cyclic triaxial test program was executed to examine the MSW's dynamic response under influential factors such as the number of loading cycles, loading frequency, confining stress, and aging. Additionally, this study focuses on finding similarities between normalized shear modulus and damping ratio curves of MSW and clayey soil. Based on the results of the current investigation and those obtained from the literature, the progression of decomposition in organic content of MSW and compaction induced by landfill operations improves the uniformity of MSW. This improvement in uniformity decreases the MSW's discreteness and, consequently, results in a higher amount of shear stiffness under cyclic loadings. However, the damping ratio results are not following a specific trend due to the unknown nature of MSW. Given the observations made by this study, MSW behaves similar to moderately plastic clay. This finding was assessed further by comparing the influential factors’ effect on MSW and clayey soil’s dynamic responses.

An insight into the liquefaction resistance of sand using cyclic undrained triaxial tests: Effect of the relative density and the loading amplitude

Abstract A stability analysis of soils prone to liquefaction based on their undrained shear-strength characteristics is an indispensable challenge in earthquake geotechnical engineering. This paper presents a laboratory study of the influence of relative density on the cyclic behavior of Chlef sand. The experimental program includes undrained, triaxial cyclic tests that were carried out for three different relative densities (Dr = 15, 50 and to 65 %) with various cyclic stress ratios (CSR = 0.15, 0.25 and 0.35). All the samples were consolidated under one initial effective confining pressure σ'c = 100 kPa. The main results show that the increases in the relative density led to significant increases in the shear strength established by an increase in the number of cycles and with an exponential rise. In contrast, it was demonstrated that the number of cycles was decreased when increasing the cyclic stress ratio due to the shearing frequency. The two main effects of the studied parameters did not have the same influence on the cyclic undrained response of the sandy soil submitted to seismic loading: an increase of the deviatoric stress due to the high relative density that participates in the increase of the loading capacity of the compacted soils by minimizing the void ratios, and an increase of the pore-water pressure that has a negative effect on the liquefaction of the soil. From the results obtained, it can be concluded that these two mechanisms led to a global increase of the maximum shearing stress.

Numerical simulation of the effect of moving loads on saturated subgrade soil

The substantial increase in excess pore pressure and plastic strain in subgrade soil due to faster and heavier trains is a major cause of track instability. Stresses that occur in track substructure during the passage of trains have not often been captured accurately due to insufficient rigour in dynamic analysis. This paper presents a numerical investigation into the plastic/dynamic characteristics of a saturated porous medium (capping and subgrade) subjected to moving axle loads. In this study, a detailed numerical analysis is described, whereby a coupled fluid-dynamic framework is developed for the saturated porous medium in conjunction with a generalized plasticity model, in order to examine the cyclic loading response of a soft subgrade soil. The constitutive model is calibrated by undrained cyclic triaxial testing carried out on a soft foundation soil retrieved from a coastal railroad site having a historical record of mud pumping. Kelvin elements are attached to the transmitting boundary to absorb wave energy and to prevent any back-propagation of waves into the saturated subgrade domain. This approach is then validated against a semi-analytical solution and wayside measurements. The results show that the stress path corresponding to the applied moving load exhibits a series of heart-shaped envelopes along which the deviator stress and mean effective stress gradually decrease with the successive loading cycles. The build-up of pore water pressure and the associated soil deformation (e.g. accumulated settlement) are exacerbated when the train speed approaches a critical velocity of the saturated subgrade. A relationship between the train speed, track settlement and drainage capacity of a sub-ballast (capping) layer is also established. As a practical guide, the influence of permeability of the capping layer is highlighted in relation to controlling track settlement for a given operational train speed.

SANISAND-MSf: a sand plasticity model with memory surface and semifluidised state

A new constitutive model for sand is formulated by incorporating two new constitutive ingredients into the platform of a reference critical state compatible bounding surface plasticity model with kinematic hardening, in order to address primarily the undrained cyclic response. The first ingredient is a memory surface for more precisely controlling stiffness affecting the plastic deviatoric and volumetric strains and ensuing excess pore pressure development in the pre-liquefaction stage. The second ingredient is the concept of a semifluidised state and the related formulation of stiffness and dilatancy degradation, aiming at modelling large shear strain development in the post-liquefaction stage. In parallel, a modified flow rule aimed at providing a better description of non-proportional monotonic and cyclic loading is introduced. With a single set of constants, for which a detailed calibration procedure is provided, this new model successfully simulates undrained cyclic torsional and triaxial tests with different cyclic stress ratios, separately for the pre- and post-liquefaction stages, as well as liquefaction strength curves based on [Formula: see text] and shear strain criteria for initial liquefaction. The successful reproduction of the sand element response under undrained cyclic shearing contributes to future applications in realistic and thorough seismic site response analysis.

Distinct Undrained Cyclic Behavior of Fine-Grained Gassy Soil at Various Initial Pore Water Pressures

Undissolved gas bubbles, which are widely formed in marine sediments, could modify the behavior of the soil. To date, the cyclic behavior of fine-grained gassy soil has been rarely studied, limiting any reliable analysis of cyclically loaded offshore foundations in fine-grained gassy seabed. This study presents a series of undrained cyclic triaxial tests on normally consolidated (NC) fine-grained gassy soil. Each sample was charged with the same amount of N2 gas before consolidation. Then, samples were consolidated to an identical mean operative stress (total stress minus pore water pressure) of 200 kPa, but at different initial pore water pressures (uw0=0–600 kPa) before cycling. Compared with a saturated sample, the inclusion of a small amount of gas bubbles can either significantly decrease the level of cyclic stiffness degradation when the initial pore water pressure uw0 is lower than a threshold value (150 kPa in this study), or vice versa. This behavior is associated with two competing mechanisms during the cyclic shearing: (1) collapse of gas-filled pores, which increases cyclic pore water pressure (CPWP), and therefore stiffness degradation; and (2) partial water drainage into gas cavities, which reduces CPWP and stiffness degradation. The former and the latter are likely to dominate at relatively high and low uw0, respectively. This implies that water depth would significantly influence the cyclic deformation and stiffness degradation of offshore foundations in fine-grained gassy sediments.

Effect of prior small to moderate seismic events on monotonic undrained shear strength of sand

In this study we investigate the effect of prior seismic shaking on the monotonic shear strength of saturated Ottawa Sand 20/30. We perform a series of stress-controlled undrained cyclic triaxial tests with different seismic intensities intentionally without causing failure, followed by drainage of the excess pore pressure and an undrained monotonic loading test to determine the undrained shear strength. The experimental data show that small to moderate seismic events that do not fail the specimen can significantly increase undrained shear strength without much change in relative density. One prior seismic event with peak ground acceleration ~ 1.3 m/s2 may increase the undrained shear strength of a specimen at ~ 10 m depth by around 30%. The results also show that as the intensity of the shaking increases, the increase in the monotonic shear strength increases. However, the strengthening effect does not increase with the number of seismic events although a small degree of global densification in the sample is observed. The results of this paper will help assess the change in static slope stability after a single or multiple small to moderate events occurred without causing initial instability.

Dynamic Characterization of Tire Derived Aggregates

Despite the recent efforts in characterizing and investigating the dynamic properties of tire-derived aggregates (TDA) and its use in civil engineering applications, the size of TDA used in most of the previous work was significantly smaller than the TDA size range mentioned in ASTM D6270 standards. There are two types of TDA, Type A and Type B, in which the maximum aggregate size of Types A and B are 200 and 450 mm, respectively. Thus, the availability of experimental data and shear modulus reduction curves for the dynamic behavior of TDA of larger sizes are deemed necessary for practical engineers to assess and investigate the behavior of such material under dynamic loads. This paper provides the results of large-scale undrained cyclic triaxial tests performed on Type A TDA at large strain amplitudes. The tests were performed under confining pressures ranging from 25 to 200 kPa and shear strain levels ranging from 0.1% to 10%. Furthermore, each test consisted of successive stages in which the number of cycles and axial strain levels varied. The shear modulus of Type A TDA has a range of 245–1,796 kPa, with a decreasing trend with increasing shear strain amplitudes. Furthermore, the dampening ratios were found to range from 11% to 23.5%. Finally, the shear modulus reduction curves were obtained through curve fitting techniques and nonlinear regression.

The effects of unloading on undrained deformation of a kaolin clay under cyclic loading

Excavation induced unloading may induce additional shear stress in soils. Such additional shear stress or unloading history may affect the long-term deformation of soft clay under subsequent cyclic loadings. A series of undrained cyclic triaxial tests were performed on a kaolin clay to study unloading effect on cyclic behaviour of the soil. The effect of unloading sequence on deformation of the clay under cyclic loading was simulated by reducing cell pressure in between loading cycles. The dependence of axial strain accumulation on the amplitude of cell pressure reduction and unloading schemes was investigated under different initial confining pressures and cyclic loading frequencies. The results indicate that reducing confining pressure accelerates the strain accumulation during subsequent loading cycles and the greater the reduction in cell pressure, the greater the accumulated strain and excess pore water pressure. Such acceleration of axial strain accumulation after unloading would be attributed to the variation of stress state and the soil's ability in memorizing the unloading history. The direction of strain accumulation is controlled by the shear stress ratio rather than the amplitude of unloading. The final accumulated strain is not much affected by unloading schemes if the samples are the same in the initial confining pressure and the amplitude of unloading. An empirical model was developed to fit the axial strain accumulation both before and after unloading. The effects of cell pressure reduction on the parameters of the empirical model were also analysed.

Micromechanical investigation of liquefaction of granular media by cyclic 3D DEM tests

In order to evaluate numerically the seismic-induced liquefaction potential of gravelly soils, three-dimensional discrete-element method cyclic undrained triaxial tests were performed in a periodic cell. The undrained tests were conducted by deforming the samples under constant volume conditions. The paper presents a detailed investigation into the mechanical phenomena occurring at the grain scale leading to the liquefaction of gravel when subjected to cyclic straining. The influence of variables characterising the granular assembly, such as inertial number, geometrical coordination number, mechanical coordination number, redundancy index and Reynolds stresses, on liquefaction is investigated. Results of the simulations show that the onset of liquefaction occurs when the granular medium becomes on average isostatic – that is the redundancy index is equal to 1, the geometrical coordination number is equal to 2 and the mechanical coordination number is equal to 3. To elucidate further the transition from solid-like to liquid-like behaviour, an analysis of how particles cluster together is presented. It is shown that, as the mean effective stress decreases, contacts are lost, with the maximum cluster size gradually reducing at an increasing rate. The loss of contacts is uniformly distributed throughout the sample and there is no break-up of the largest cluster into smaller clusters.

A multisurface kinematic hardening model for the behavior of clays under combined static and undrained cyclic loading

AbstractIn dynamic geotechnical problems, soils are often subjected to a combination of sustained static and fast cyclic loading. Under such loading conditions, saturated and normally consolidated clays generally experience a build‐up of excess pore water pressure along with a degradation of stiffness and strength. If the strength of the soil falls below the static stress demand, a self‐driven failure is triggered. In this paper, a constitutive model is presented for the analysis of such problems, based on a general multisurface plasticity framework. The hardening behavior, the initial arrangement of the surfaces, and the nonassociated volumetric flow rule are defined to capture important aspects of cyclic clay behavior. This includes nonlinear hysteretic stress‐strain behavior, the effect of anisotropic consolidation, and the generation of excess pore water pressure during undrained cyclic loading along with a degradation of stiffness and strength. The model requires nine independent parameters, which can be derived from standard laboratory tests. A customized experimental program has been performed to validate the model performance. The model predictions show a good agreement with test results from monotonic and cyclic undrained triaxial tests, in particular with respect to the strain‐softening response and the number of loading cycles to failure. A procedure for a general stress‐space implicit numerical implementation for undrained, total stress‐based finite element analyses is presented, including the derivation of the consistent tangent operator. Finally, a simulation of the seismic response of a submarine slope is shown to illustrate a possible application of the presented model.

Liquefaction resistance of fibre-reinforced silty sands under cyclic loading

Whether the so-called double porosity in soils with a loose and natural packing state is a concept with real-world implications is a fundamental yet controversial question in the study of cyclic undrained shear behaviour of fibre-reinforced silty sands. An attempt is made here to clarify the question by means of particle-level modelling combined with 41 undrained cyclic triaxial shear tests. The study shows that the initial Random Loose Packing changes to Random Close Packing and then Close Packing with silt content increments. The transition from random to close packing occurs at a threshold silt content which is relatively lower in coarser sands. For sands with <40% silt content, the rate of pore pressure growth with loading-unloading cycles increase with silt content increment. Reverse trend applies to silty sands with >40% silt content. Irrespective of fine content, fibres tend to sit deep into the silt pellets and encrust the macro-pore spaces. Generally, increasing fibre content leads to an increase in the average number of contacts per particle, dilation and easier dissipation of excess pore water pressure, a decrease in contact forces and improved liquefaction resistance. For sands with >40% silt content, effectiveness of fibre reinforcement diminishes with increasing sand median size.

Accumulated Plastic Strain Behavior of Granite Residual Soil under Cycle Loading

Abstract In this study, the accumulated plastic strain (APS) of granite residual soil under cyclic loads is investigated by a series of undrained cyclic triaxial tests. Granite residual soil is a s...

Particle breakage evolution during cyclic triaxial shearing of a carbonate sand

Particle breakage of carbonate sand under cyclic loading might be of interest in some circumstances, while few research results were reported. Drained and undrained cyclic triaxial tests terminated at different loading cycles were conducted on a carbonate sand to investigate the evolution characteristics of particle breakage during cyclic shearing. Considerable breakage was observed after successive cyclic triaxial shearing at moderate confining pressure levels (≤200 kPa). Abrasion of surface asperities and small sharp edges was found to be the primary pattern of particle breakage and the particle size distribution after cyclic shearing showed an increased mass content of fine particles. In drained cyclic tests with constant confining pressure and cyclic stress amplitude, particle breakage appeared to accumulate at a decreasing rate with increasing loading cycles, and the development of particle breakage with loading cycles can be fitted by a logarithmic equation. In undrained cyclic tests, particle breakage exhibited more complicated accumulation patterns because the effective confining pressure and cyclic strain amplitude varied greatly. A cycle-by-cycle incremental breakage evolution model was established, and the model revealed that the incremental breakage generated in subsequent loading cycles decreases with accumulated particle breakage and increases with increasing effective confining pressure and cyclic shearing intensity. The model was validated by comparing the model predictions with the particle breakage evolution observed during undrained cyclic triaxial tests.

Undrained cyclic responses of granulated rubber-sand mixtures

Undrained cyclic responses of rubber-sand mixtures are essential for its applications in earthquake-prone areas. Hence, the present study is intended to examine the liquefaction behaviour and modeling the undrained cyclic responses of granulated rubber-sand mixtures with size of sand and granulated rubber less than 2 mm. The stress controlled undrained cyclic triaxial tests followed by undrained monotonic tests were carried out on mixtures with rubber content 0% (pure sand), 10%, 20%, 30%, 50%, 75%, and 100% (pure rubber) to examine liquefaction and post-liquefaction behaviour of the mixtures. The test results show that the mixture possesses higher liquefaction resistance when rubber content is between 30% and 50%. The post-liquefaction behaviour of the mixtures identified as pseudo-elastic-hardening and its corresponding modulus is found to vary marginally with its static modulus. In addition, the post-liquefaction strength of the mixtures is observed to be more than that of sand at the lower axial strain. Further, the undrained responses such as hysteretic behaviour and excess pore water pressure are modeled using Masing’s rule and the relation between degradation index (δ) and excess pore water pressure ratio (ru), respectively. The proposed model effectively predicts the cyclic behaviour of mixtures with rubber content between 10% and 75%.

Energy based cyclic strength for the influence of mineral composition on artificial marine clay

The strength of marine clay under cyclic loading is affected by its mineral composition, which must be considered in engineering design. Consolidated undrained cyclic triaxial tests were conducted on specimens from two groups of samples of artificial marine clays consisting of four pure minerals (quartz, albite, Na-montmorillonite and kaolinite) in mass proportion (Qc:Ac:Mc:Kc). The study of two test groups was to identify differences in the properties of the soils due to montmorillonite and kaolinite (MKDT group) and the differences due to the nonclay minerals (NCDT group). The results demonstrated the following main points. The power function curves for cyclic strength derived from conventional strain failure criteria show that both montmorillonite and clay minerals significantly increase cyclic strength. Furthermore, the energy based viscous energy dissipation ratio (VEDR) was introduced to partition cyclic loading process into two stages: competition and rapid increasing. There were two critical points in the cyclic loading procedure, VEDRmin and VEDRbreakpoint, that represent initial energy dissipation and turning-point energy dissipation. Therefore, by connecting the VEDRbreakpoint points, the linear VEDR cyclic strength curve (NVEDR-VEDRbreakpoint) was created with two parameters, slopVEDR and VEDRintercept. By analogy with the parameters of conventional cyclic strength curve (a, b and CSRmin), slopVEDR and VEDRintercept respectively reflect that influence of cyclic loading and mineral composition on VEDRbreakpoint. Additionally, it is also demonstrated that both montmorillonite and clay minerals reinforce VEDR cyclic strength just like the conventional one. This research makes a major contribution to our understanding of cyclic strength by accounting for energy dissipation.

Investigation on the mechanical properties of a calcareous sand: the role of the initial fabric

This study examines the effect of the initial fabric on the coefficient of the lateral earth pressure at rest K0, the undrained monotonic loading strength and the liquefaction resistance of a calcareous sand from a reclamation land in Persian Gulf. K0 consolidation, undrained compression and extension and cyclic undrained loading triaxial tests are performed on laboratory samples reconstituted by air and water pluviation, dry and moist tamping and dry funnel deposition methods. Test results show that the air pluviation and moist tamping samples own the highest and the lowest K0 respectively. All the samples at medium loose and medium dense states show strain hardening when subjected to undrained monotonic loading. The air pluviation samples are more contractive than the other samples at the phase transformation points and the moist tamping samples exhibit an over-consolidated behavior. In the cyclic loading tests, the air pluviation and the moist tamping samples exhibit the lowest and the highest liquefaction resistance. It is shown that the evaluation and comparison of the cyclic undrained strength of various sands should take the sample preparation method into consideration scrupulously. The test results also indicate that although the mechanical property of soil sample is influenced by the fabric differences induced by sample preparation method, other factors such as homogeneity and stress history should not be neglected.

Liquefaction resistance of sand amended with biochar

Biochar is a solid carbon material produced by heating organic biomass in the absence of oxygen through a process known as pyrolysis. Scientists and policy makers have recognised its potential role in carbon sequestration, reducing greenhouse gas emissions, renewable energy, waste mitigation and as soil amendment. To date, most studies related to biochar application to soil have focused mainly on the agronomic benefits, while little attention is paid on its effects on soil properties from geotechnical point of view. Considering that biochar can be produced from biomass, its use would fit satisfactorily the current trends of recycling wastes for ground improvement and liquefaction mitigation. To address this, the effect of adding various proportions by weight of biochar, derived from poultry litter, on the liquefaction resistance of sand is investigated through undrained cyclic triaxial tests. The findings suggest that, contrary to other earlier published reports using another type of biochar, adding poultry litter biochar to sand decreases its liquefaction resistance in a similar manner as adding non-plastic fines. The results highlight the fact that the type of biochar used as soil amendment is important in determining whether the liquefaction resistance of the host sand will improve or not.