Cyclic Soil Behavior Research Articles

Cyclic modeling of unsaturated sands using a pore‐scale hydromechanical approach

AbstractDetermining proper strain‐dependent shear modulus and damping ratio for soils is of utmost importance when investigating their response to cyclic loads. Experimental studies on the effect of the degree of saturation and suction on the shear modulus at large strain amplitudes are scarce due to the complexities involved in testing such soils. Furthermore, the previously presented micromechanical models for the cyclic behavior of unsaturated soils lack some of the required features of soil pore skeleton essential to model unsaturated soils’ hydromechanical behavior. This paper is, thus, aimed at addressing this shortcoming by incorporating a pore‐scale numerical method that couples the discrete element simulation of the solid phase and the fluid pore network to capture the cyclic behavior of unsaturated sands. To this end, the model is first calibrated to determine the micro‐scale parameters using experimental results from static drained triaxial compression tests on dry and saturated sand samples. Next, the coupled model is employed to simulate the observed behavior during cyclic triaxial tests on unsaturated sands. A linear dependence of the plastic rolling coefficient and the interparticle friction angle on the degree of saturation is proposed from simulations of suction‐controlled cyclic triaxial tests. Variation of shear modulus with shear strain amplitude and degree of saturation indicates a continuous increase in the shear modulus with the decrease in saturation. In contrast, the trend for the damping ratio is the opposite. Finally, closed‐form relationships are proposed based on the simulation results for the shear modulus and damping ratio of unsaturated soils.

Memory repositioning in soil plasticity models used in contact problems

We aim to enhance the stability of finite element models of dynamic structural contact with multiphase granular soils which are described by advanced soil plasticity models that can simulate monotonic and cyclic behaviour of multiphase soils. Often, numerical oscillations cannot be avoided in these contact models and can cause advanced soil models to significantly overshoot stress, leading to unrealistic discontinuities in the stress paths. This situation can challenge the stability of the stress integration scheme and the global finite element solver and lead to the early termination of the analysis. We specifically address the issue of stress overshooting by presenting novel solutions and the corresponding stress integration schemes for a representative soil model for unsaturated granular soils. Also, several examples are provided to evaluate the integration scheme and show the advantages and limitations of the proposed overshooting solutions in solving a contact-impact problem involving unsaturated granular soils.

Earth pressure model to predict the long-term performance of integral abutment bridge

Integral abutment bridges (IAB), especially the short to medium-span IABs, have become more popular throughout the years in Australia as well as globally. IABs have advantages over traditional bridges in terms of their construction and maintenance costs due to the elimination of expansion joints. However, the thermal expansion can develop significantly larger earth pressure behind the abutment, thus leading to excessive forces (i.e. moment and shear force) to the foundation, which are not considered during the design process and can cause cracking and failures, eventually. It is observed from the field monitoring of IABs that the earth pressure model used to estimate the pressure distribution is not adequate to capture possible variations. Further, the performance of IABs highly depends on the complex interaction of abutment-backfill and soil-foundation and the time-dependent and cyclic behaviour of backfill and foundation soils. In this paper, nonlinear finite element model of an IAB considering the time-dependent effects of materials is presented to simulate long-term responses due to thermal loading. The developed IAB model results are validated using field monitoring data and parametric study is performed including the geometry of IAB, thermal loading, and soil properties. The results are used to investigate the functional relationship between input parameters and long-term responses which are further utilised to develop a new earth pressure distribution model for the design and performance assessment of IABs.

A thermodynamically consistent two surface/bubble thermo-mechanical model considering thermal and mechanical cyclic behaviour of fine-grained soils

The formulation of a two surface/bubble thermo-mechanical constitutive model consistent with the principles of thermodynamics is presented. This allows plastic deformations inside the outer yield surface, resulting in a smooth stress–strain prediction and progressive cyclic deformations. This is achieved by the translation of the inner yield surface (also known as the bubble surface) with the stress state of the soil, inside the outer yield surface, by using a kinematic rule. The constitutive equations, including the hardening rules, are derived by specifying a Gibbs-type energy potential and a rate of dissipation potential function, ensuring thermodynamic consistency. The kinematic rule is divided into isothermal and non-isothermal parts. With the isothermal component, the model is capable of capturing the hysteresis behaviour of soils during cyclic mechanical loading. With the non-isothermal part, the model is able to predict the shakedown behaviour of soils observed when they are subjected to heating–cooling cycles. The performance of the model is compared with various experimental data for isothermal and non-isothermal conditions, and is shown to be in good agreement.

Cyclic behaviour of stratified soil under liquefied states

A substantial amount of work on the cyclic behaviour of cohesionless soil has been performed after neglecting the reality of stratification existing nearby marine structures or alluvial plains. This complicated mechanism of stratified soil failure on earthquake-induced soil liquefaction is affected significantly by the presence of a less permeable soil layer. Several past studies investigated that under the action of dynamic loads, the presence of a silt layer in homogeneous sandy soil crucially modifies the pore pressure dissipation characteristics, axial strain rate and stress–strain behaviour of the whole stratified specimen. In the present study, cyclic behaviour of sand specimen interlayered with silt layer has been presented in respect of its pre-and post-liquefaction behaviour. Undrained stress-controlled cyclic triaxial tests have been performed on homogeneous sand specimens and on specimens interlayered with a silt layer, placed at H/4, H/2 and 3H/4 (where H is the height of the specimen from the top) to signify the role of placement depth. The instability and failure of such specimens have been compared using the failure line and phase transformation line. Few key observations suggested that the number of liquefaction failure cycles enhanced two times and secant modulus (under post liquefied state) improved by 4.8 times when the placement depth of the silt layer increased from H/4 to 3H/4 under similar loading conditions. Additionally, the role of initial static shear stress has been investigated at three different confining pressures in a few stratified specimens. It has been observed that failure of the stratified specimen is due to the obstruction of pore water movement caused by the presence of the silt layer. A comparison of the present work has been made with significant studies using liquefaction resistant curves to ensure the efficacy of this study.

Characterizing and Modeling the Coupled Hydro-Mechanical Cyclic Behavior of Unsaturated Soils Using Constant Water Content Oedometer and Direct Shear Tests

Most transportation infrastructures are constructed on compacted soils that are typically unsaturated above the groundwater table. The soils are subjected to cyclic traffic loadings and seasonal wetting–drying cycles. Although problems associated with unsaturated soils are ubiquitous in the US, coupled hydro-mechanical analysis is rarely included in the design/analysis of transportation geosystems. This can be attributed to two main reasons: (a) there are no simple devices/methods which can be used to rapidly characterize stress–strain behavior for unsaturated soils, and (b) there is a lack of a constitutive model to study coupled hydro-mechanical cyclic behavior for unsaturated soils in a consistent way. This paper takes advantage of the recent advancements in suction measurement and constitutive modeling to overcome these limitations. In this paper, conventional oedometer and direct shear tests for saturated soils are modified to characterize stress–strain behavior of unsaturated soils under cyclic undrained loading conditions. Then, series of constant water content cyclic oedometer and direct shear tests are performed to characterize the hydro-mechanical behavior of a silty soil. Moreover, methods are developed to use results from both tests to calibrate parameters for a recently proposed hydro-mechanical constitutive model. The paper also compares the model predictions with the measured results. Results indicate that the model is able to satisfactorily predict the hydro-mechanical hysteresis behavior of the soil. With developments in equipment, constitutive models, and analysis, it is now possible to fully characterize the hydro-mechanical behavior of unsaturated soils in a more efficient manner.

Cyclic behavior of saturated soil: a new 3D model

The role of pore pressure cannot be neglected for saturated soils in a strong earthquake, which is characterised by a large amplitude and duration. Indeed, pore water pressure controls phenomena such as cyclic mobility and liquefaction due to the loss of soil strength and stiffness. This can lead to a fast decrease of effective stresses and permanent deformations in the soil causing severe damage to structures. Motivated by experimental observations, a plasticity model is developed for capturing the main characteristics of cyclic mobility. This model extends an existing multi-surface plasticity formulation and is based on the relationship between the pore pressure and the shear work. The three-dimensional stress state of the material is considered. The proposed model allows to model the effect of cyclic loadings on saturated soils and to assess the multidirectional effect. Comparison between the modelling results and the experimental ones from triaxial and torsion tests are made to show the validation and the capacity of the current model.

Cyclic behavior of cement-stabilized sabkha soil

Cyclic behavior of cement-stabilized sabkha soil

Influence of fines on the monotonic and cyclic shear behaviour of volcanic soil “Shirasu”

Drained and undrained monotonic and undrained cyclic triaxial tests have been carried out on reconstituted samples of Shirasu originally deposited from pyroclastic flows in the Kagoshima area, Japan. This material contains 20%–30% fines derived from the same minerals as the coarse grains. Well-graded fines can form a weakly interlocked structure in loose Shirasu separating the coarse grains and resulting in a weak liquefiable soil. In order to clarify the mechanical characteristics of Shirasu, a series of triaxial tests were carried out on the original Shirasu and a material whose fines had been washed out. The “fines” Shirasu was weak with its properties highly dependent on the confining stress while the “no-fines” Shirasu had a high strength which decreased with increasing confining stress due to breakage of asperities. The presence of fines between coarse grains altered the location of critical state line of Shirasu. Under undrained cyclic loading and low confining pressures, the weakly interlocked structure of medium-dense “fines” Shirasu collapsed resulting in contractive behaviour and liquefaction. As the confining pressure was increased, this weak fine structure was compressed and the soil structure became stiffer under cyclic loading. In practical terms, this means that Shirasu which is placed as a loose hydraulic fill will be prone to liquefaction. The undrained cyclic response of medium-dense “no-fines” Shirasu was similar to that of dense “fines” Shirasu. Thus, the removal of fines was equivalent to compacting the material to a relatively high density.

Cyclic behavior of late quaternary alluvial soil along Indo-Gangetic Plain: Northern India

The A.D. 1803 and 1934 Bihar-Nepal border earthquake affected Indo-Gangetic Plain with evidences of liquefaction in cities like Patna, Varanasi, Agra, and Delhi in historical past. Recent strong shaking all along the Indo-Gangetic Plains and seismic induced damage to the buildings in Bihar during Mw 7.8 Gorkha earthquake raises the concern for site specific liquefaction potential estimation of alluvial soils. Cyclic triaxial tests were conducted on soil samples from Kanpur, Allahabad, Patna city to know the cyclic behavior, estimate the dynamic soil properties and the effect of relative density, confining pressure and frequency of loading on the cyclic behavior of the soil tested. The test results indicate the cyclic strength of Allahabad soil is less than Patna and Kanpur soil. The Allahabad soil with 80% sand, 10% silt and clay each is more prone to liquefaction than Kanpur soil (82% silt, 16% clay and 2% sand) and Patna soil (10% Kankar, 95% sand, 5% silt). This study indicates soils having sand with silt percentage are more liquefiable than clean sand or silty soil. It can be concluded that the soil of Allahabad and Patna city is more prone to liquefaction than Kanpur soil.

Influence of stress history on the cyclic behavior of compacted soils in the frozen state: Deviator stress history

Observation of the cyclic behavior of compacted soils in a frozen state is required for assessing the dynamic stability of subgrades or embankments induced by earthquakes or traffic in cold regions, in which the compacted frozen soils have often experienced deviator stress history before applying cyclic stress. Therefore, strain-controlled monotonic triaxial tests followed by stress-controlled cyclic triaxial tests were carried out on compacted frozen soils to investigate the influence of deviator stress history on the cyclic behavior of such soils. The results shows that nonlinear and accumulated behaviors are represented in the stress-strain response of frozen soils regardless the amounts of residual strain induced by stress history. Although the volume fluctuations along with the general path are observed in the cyclic loading sequence, the general path seems consistent with volume changes during the monotonic loading stage, which potentially indicates that the plastic flow characteristics of this frozen soil are independent of the axial loading models (monotonic or cyclic loading). Moreover, an increase in the residual strains induced by stress history led to a decrease in the axial strain accumulation rate and to an increase in cyclic stiffness due to strain hardening induced by preloading. A previously proposed model for predicting the changes in the accumulated strain with the cyclic loading process was found to be applicable to compacted frozen soils regardless of the amounts of residual strain induced by stress history.

Analytical Solution for One-Dimensional Nonlinear Consolidation of Saturated Double-Layered Soil Subjected to Cyclic Loadings

Cyclic loading-induced consolidation behavior of soft soil is of great interest for the analysis of offshore and onshore structures. In this study, an analytical solution for one-dimensional (1D) nonlinear consolidation of saturated double-layered soil under various types of cyclic loadings such as trapezoidal cyclic loading, rectangular cyclic loading, and triangular cyclic loading was derived. The proposed solution was subsequently degenerated into solutions for special cases and compared to the existing solutions. The degenerate solutions show good agreement with the existing results, which proves that the proposed solutions are more general ones for 1D nonlinear consolidation of saturated soils under time-dependent loading. Finally, a comprehensive parametric study was conducted to investigate the influences of different layer parameters, drainage conditions, and loading parameters on nonlinear consolidation of saturated double-layered soil under cyclic loadings.

Cyclic behavior of bio-cemented soils using relatively large grains

Cyclic behavior of bio-cemented soils using relatively large grains

Cyclic simple shear behaviour of saturated and moist sandy soils

ABSTRACT Liquefaction and settlement of sandy soils cause significant damage during earthquakes. In this research, cohesionless soils of Kutch region with history of large earthquakes are explored. Twenty-six soil samples were collected from different locations of Kutch region and tested under saturated and moist conditions by performing two series of Electromechanical Dynamic Cyclic Simple Shear (EMDCSS) tests. In series I, the liquefaction characteristics of saturated samples were observed to be dependent on fines content and plasticity index. Kutch soils with non-plastic fines exhibited low liquefaction resistance and showed increased resistance at higher FC; however, for sands with plastic fines, PI rather than FC controlled the cyclic degradation. Saturated sandy soils with non-plastic fines exhibited lower shear stress mobilisation, higher pore pressure and larger degradation as compared to sands with clay content. In series II, the settlement characteristics of moist samples at constant normal stress revealed decreased axial deformation and increased mobilised shear stress with increased FC and PI. Silty-sands exhibited higher deformations and larger strength as compared to clayey-sands. The EMDCSS tests at saturated and moist conditions revealed Kutch soils to be prone to liquefaction and large settlements, respectively.

The effects of unloading on drained cyclic behaviour of Sydney sand

New excavation or tunnelling affects the stress state of soils in ground. The change of stress state due to excavation may affect the cyclic behaviour of soils. Cyclic loading, such as traffic and earthquake loading, induced ground deformation may be greater than expected if such effect is not considered. A series of cyclic triaxial tests were performed on Sydney sand with different relative densities. The effect of unloading sequence on deformation of the sand under cyclic loading was simulated by reducing lateral stress in steps between loading cycles. The dependence of strain accumulation on the magnitude of confining pressure reduction and on unloading stress paths was studied. The results indicate that the sand has a memory of stress history and the stress history of such unloading enlarges the strain accumulation during the subsequent cycles, and the greater the reduction of lateral stress, the greater the accumulated strain. Under cyclic loading, the accumulated axial strain could increase nonlinearly or linearly with the ratio of unloading magnitude to initial mean effective stress, depending on the stress state before cyclic loading. The unloading stress paths have limited effects on the final accumulated strain if the initial and final stress states are the same. The variation of strain accumulation direction attributes to the change of average stress ratio resulting from lateral stress reduction, but hardly depends on relative density and unloading stress paths. The strain accumulation direction after unloading roughly agrees with the modified Cam Clay flow rule.

Large strain dynamic characteristics of quaternary alluvium sand with emphasis on empirical pore water pressure generation model

The present study focuses on the cyclic behaviour of cohesionless soil collected from the quaternary alluvium deposit at the Middle Ganga Plain (MGP). A series of strain-controlled cyclic triaxial tests have been carried out on collected soil samples at various effective confining stresses, shear strain amplitudes and motion frequencies to estimate the dynamic parameter at large strain. From the results, it has been shown that dynamic properties and liquefaction strength substantially affected by the shear strain amplitude of input motion. However, effective confining stress and motion frequency have no significant effect on dynamic properties and liquefaction strength at large strain. Regression equations have been developed for dynamic and liquefaction strength parameters for the studied soil. It has been found that the consideration of asymmetricity in the shape of hysteresis loops significantly influences the damping ratio estimation at a particular shear strain. Another novel aspect that has been presented in this study is the effect of effective confining stress on the EPWP model parameter F using a mathematical equation. The regression equation for model parameter F proposed in this study has been validated by predicting the maximum EPWP development of studied soil and other quarternary alluvium soils available worldwide.

Cyclic Behaviour of Palu Sandy Soils in Cyclic Simple Shear Test

A 7.5-moment magnitude earthquake hit Palu, Central Sulawesi, Indonesia, in September 2018. This earthquake caused many damages and casualties, including tsunami and liquefaction. Following these events, Palu sand’s cyclic properties were investigated under cyclic simple shear testing conditions, which could convincingly portray the real seismic ground shaking under repeated shear force. All the tests were performed under the frequency of 1.0Hz with varied relative densities and cyclic stress ratio (CSR). The results show that grain size distribution plays a significant role in liquefaction resistance of sandy soils tested-the soils tested under higher CSR need fewer cycles to liquefy. Furthermore, soils which in loose conditions tend to have lower liquefaction resistance.

Undrained cyclic response of a dense saturated sand with various grain sizes and contents of nonplastic fines: Experimental analysis and constitutive modeling

The densification can increase the liquefaction resistance of sands. However, in most engineering practice, sands are not pure and contain a significant amount of fines with particle diameter smaller than 0.075 mm. Thus, it is necessary to quantitatively evaluate the influence of fines on the undrained cyclic behavior of dense sandy soils. In this study, a series of undrained cyclic triaxial tests were conducted on the dense saturated sand with various mean grain sizes and contents of nonplastic fines. A unified constitutive framework is modified to improve the capability of simulating the cyclic mobility behavior of sandy soils. The results indicate that the effect of the mean grain size on the cyclic stress ratio required to cause 5% double-amplitude axial strain for sandy soils depends on the amount of nonplastic fines added. Moreover, a good correlation between the cyclic resistance ratio and the initial value of the equivalent granular state parameter is obtained for various fines contents and mean grain sizes of nonplastic fines. The influence of the fines content and mean grain size of nonplastic fines on the liquefaction resistance of sandy soils can be reasonably characterized by the constitutive framework using a set of unique parameters. Additionally, the capability of the constitutive framework for describing the influence of the fines content on the cyclic instability behavior of sandy soils is also evaluated against the experimental data in the literature.

Influence of Input Assumptions on the Evaluation of the Seismic Performance of Earth Dams

ABSTRACT The seismic performance of earth dams can nowadays be performed via dynamic analyses using constitutive models of sufficient accuracy in describing cyclic soil behavior. However, a number of assumptions different from soil model affect the problem as a whole. In this paper, a 2D model of a simplified homogeneous earth dam is developed, to assess the influence of bedrock compliance, vertical component of ground motion, stabilizing berms, and initial pore water pressure distribution on its seismic performance, thus providing some guidance on the choices that should be adopted for a safe assessment of the seismic performance of existing earth dams.

Analysis of undrained cyclic response of saturated soils

Some previous constitutive models introduce many sophisticated concepts and new parameters to characterise cyclic behaviour of saturated soils, while other simpler models show incomplete theoretical developments which limit their applications. This study aims to improve previous studies by revising the way the yield surface responds to cyclic loading under undrained conditions, i.e., the yield surface is assumed to change its shape while maintaining its size during unloading. The proposed hypothesis is used to examine a series of undrained cyclic tests where various cohesive soils are examined with an acceptable agreement. Based on this process, empirical relationships between the model parameters and given load and soil characteristics are formed, thus enabling the input parameters to be determined rigorously. The analysis shows that soil can reach an unstable state where the excess pore pressure (EPP) and axial strain develop rapidly when the cyclic stress ratio reaches a critical degree. A higher loading frequency requires a larger number of cycles but in shorter timeframe to initiate instability of the soil. The lower the plasticity of the soil, the larger and faster the accumulation of EPP and axial strain whereas increasing the initial shear stress can make soil unstable earlier.