Liquefaction Response Research Articles

Understanding the influence of drained cyclic preloading on liquefaction resistance of sands using DEM-clump modeling

The soils in situ are subjected to various types of preloading histories. Extensive work has been devoted to understanding the impact of undrained preloading with different strain histories on the reliquefaction resistance of sands. This study primarily examines the effects of drained cyclic preloading histories on the liquefaction resistance of soils using DEM-clump modeling. The effects of preloading stress path and preloading deviatoric stress amplitude on the drained cyclic behavior and subsequent undrained liquefaction response are discussed. Moreover, the evolution of two microscale descriptors, including coordination number Z and fabric anisotropy degree ac, during the total process is analyzed. The results demonstrate that a smaller preloading stress amplitude and an increasing preloading cycle generally increase the liquefaction resistance of sandy soils. In comparison, a larger preloading stress amplitude significantly reduces the liquefaction resistance. We also reveal that drained cyclic preloading histories induce soil samples with different relative densities and fabrics. The relationship between relative density and liquefaction resistance of soils is not unique. Essentially, Z and ac are good indexes for determining the liquefaction resistance of soils with various drained cyclic preloading histories. The primary objective of this study is to elucidate the micromechanical effects of drained cyclic preloading on the liquefaction resistance of sandy soils.

Effect of Non-plastic Fines Content and Gradation on the Liquefaction Response of Chlef Sand

Effect of Non-plastic Fines Content and Gradation on the Liquefaction Response of Chlef Sand

Spatial variability of shear wave velocity: implications for the liquefaction response of a case study from the 2010 Maule Mw 8.8 Earthquake, Chile

Assessing the potential and extent of earthquake-induced liquefaction is paramount for seismic hazard assessment, for the large ground deformations it causes can result in severe damage to infrastructure and pose a threat to human lives, as evidenced by many contemporary and historical case studies in various tectonic settings. In that regard, numerical modeling of case studies, using state-of-the-art soil constitutive models and numerical frameworks, has proven to be a tailored methodology for liquefaction assessment. Indeed, these simulations allow for the dynamic response of liquefiable soils in terms of effective stresses, large strains, and ground displacements to be captured in a consistent manner with experimental and in-situ observations. Additionally, the impact of soil properties spatial variability in liquefaction response can be assessed, because the system response to waves propagating are naturally incorporated within the model. Considering that, we highlight that the effect of shear-wave velocity Vs spatial variability has not been thoroughly assessed. In a case study in Metropolitan Concepción, Chile, our research addresses the influence of Vs spatial variability on the dynamic response to liquefaction. At the study site, the 2010 Maule Mw 8.8 megathrust Earthquake triggered liquefaction-induced damage in the form of ground cracking, soil ejecta, and building settlements. Using simulated 2D Vs profiles generated from real 1D profiles retrieved with ambient noise methods, along with a PressureDependentMultiYield03 sand constitutive model, we studied the effect of Vs spatial variability on pore pressure generation, vertical settlements, and shear and volumetric strains by performing effective stress site response analyses. Our findings indicate that increased Vs variability reduces the median settlements and strains for soil units that exhibit liquefaction-like responses. On the other hand, no significant changes in the dynamic response are observed in soil units that exhibit non-liquefaction behavior, implying that the triggering of liquefaction is not influenced by spatial variability in Vs. We infer that when liquefaction-like behavior is triggered, an increase of the damping at the shallowest part of the soil domain might be the explanation for the decrease in the amplitude of the strains and settlements as the degree of Vs variability increases.

Effects of partial saturation on the liquefaction response of two Christchurch deposits

Effects of partial saturation on the liquefaction response of two Christchurch deposits

Energy-based evaluation of seismic liquefaction response of sand in level and sloping ground

Energy-based evaluation of seismic liquefaction response of sand in level and sloping ground

Ground-motion effects on liquefaction response

This article evaluates the influence of ground-motion characteristics on the liquefaction response of free-field level-ground deposits. Ground motions imposed on liquefiable soils have historically been characterized by the peak ground acceleration (PGA). In simplified procedures for liquefaction evaluation, the use of the ground surface PGA can be justified by the fact that it is closely related to the peak shear stresses developing in the critical zone for liquefaction manifestation, at shallow depths. In nonlinear dynamic analysis (NDA), however, such simplified characterization of the input motion using the bedrock-level PGA can result in large record-to-record variability in the computed response. Record-to-record variability can be substantially reduced by employing more appropriate ground-motion intensity measures (IMs) for specific aspects of the liquefaction response observed in NDA. Among 25 IMs examined in this study, the Modified Acceleration Spectrum Intensity (MASI), defined as the integral of the acceleration spectrum over periods 0.1–1.5 s, is found to be the most efficient IM for the prediction of the pore-pressure response of liquefiable deposits, whereas Velocity Spectrum Intensity (VSI) ranks among the best-performing IMs for response parameters related to ground deformations. Importantly, such “multiple-period spectrum IMs” are shown to perform consistently better than several highly-regarded time-integrated IMs (e.g. Arias intensity, CAV). Conclusions and recommendations are drawn on the basis of a comprehensive series of NDAs involving 180 input motions and 13 deposit models based on characteristic soil profiles from Christchurch.

An Experimental Investigation on Shear Strength and Liquefaction Response of Pond Ash for Road Embankment Construction

An Experimental Investigation on Shear Strength and Liquefaction Response of Pond Ash for Road Embankment Construction

Role of geofoam inclusions on the liquefaction resilience of transportation geostructures

Though the effectiveness of geofoam buffers for improving the dynamic load response and seismic performance of road embankments and retaining walls is well-established, their role on soil liquefaction is not investigated by many. This study explores the potential of Expanded Polystyrene (EPS) geofoam inclusions for liquefaction mitigation in sands through a series of stress-controlled constant volume cyclic simple shear tests. The study quantifies the increase in liquefaction resistance of sand with geofoam inclusions and reduction in modulus degradation and shear deformations and increase in energy dissipation with loading cycles. Effects of geofoam density and thickness of the layer on the liquefaction response were also investigated through systematic series of experiments with geofoam of three different densities and two different thicknesses. Findings from this experimental study suggest that providing a thick low-density geofoam layer provided the maximum benefit among all the inclusions. Fundamental mechanisms governing this improved response are explored through a series of bender element tests. Results from this study confirm the effectiveness of geofoam buffers in mitigating liquefaction in granular soils and recommend their use in road embankments and retaining walls being constructed in zones of high seismicity to avoid liquefaction and associated lateral spreading failures in these structures.

Select liquefaction case histories from the 2001 Nisqually, Washington, earthquake: A digital data set and assessment of model performance

While soil liquefaction is common in earthquakes, the case-history data required to train and test state-of-practice prediction models remains comparatively scarce, owing to the breadth and expense of data that comprise a single case history. The 2001 Nisqually, Washington, earthquake, for example, occurred in a metropolitan region and induced damaging liquefaction in the urban cores of Seattle and Olympia, yet case-history data have not previously been published. Accordingly, this article compiles 24 cone-penetration-test (CPT) case histories from free-field locations. The many methods used to obtain and process the data are detailed herein, as is the structure of the digital data set. The case histories are then analyzed by 18 existing liquefaction response models to determine whether any is better, and to compare model performance in Nisqually against global observations. While differences are measured, both between models and against prior global case histories, these differences are often statistically insignificant considering finite-sample uncertainty. This alludes to the general inappropriateness of championing models based on individual earthquakes or otherwise small data sets, and to the ongoing needs for additional case-history data and more rigorous adherence to best practices in model training and testing.

Liquefaction behavior evaluation of a multi-layered site with fines-dominated soils

Characterization of liquefaction response in terms of triggering and manifestation at sites with soils containing significant amounts of fines is critically important. Saturated fines-dominated soils, that are known as liquefaction-susceptible materials, would represent a range of extreme responses to earthquake excitations from cyclic mobility to cyclic liquefaction causing excessive displacements. In a multi-layered soil profile, the interaction of adjacent layers in porewater pressure redistribution along the site profile plays an important role in liquefaction response. In this study, an advanced Nonlinear Dynamic Analysis (NDA) procedure in predicting the liquefaction mechanism and manifestation at a site with multiple fines-dominated soil layers is presented. The procedure specifically aims at simulating the interactions in a multi-layered system containing both sand-like and clay-like materials. The liquefaction data recorded by Wildlife Liquefaction Array (WLA) in 1987 Superstition Hills Earthquake (M = 6.6) was deployed to validate the NDA procedure. WLA site consists of sandy silt, silty sand, clayey silt, silty clay, and silt deposits in its upper 20 m and has provided invaluable records of porewater pressure and ground motions. Two critical-state-based constitutive models, PM4Silt and PM4Sand, in a coupled dynamic-fluid finite difference platform were employed. Calibration of the constitutive models was conducted using Cyclic Direct Simple Shear (DSS) test single-element modeling. The simulated response of the site from the proposed approach was compared with those of other NDA procedures conducted on this case history in terms of liquefaction parameters such as excess porewater pressure ratio and maximum shear strain. These comparisons revealed that incorporating multi-layer effects in an advanced NDA procedure can enhance the liquefaction behavior predictions at sites with fines-dominated materials.

Calibration of an elastoplastic model of sand liquefaction using the swarm intelligence with a multi-objective function

According to post-seismic observations, spectacular examples of engineering failures can be ascribed to the occurrence of sand liquefaction, where a sandy soil stratum could undergo a transient loss of shear strength and even behave as a “liquid”. Therefore, correct simulation of liquefaction response has become a challenging issue in geotechnical engineering field. In advanced elastoplastic models of sand liquefaction, certain fitting parameters have a remarkable effect on the computed results. However, the identification of these parameters, based on the experimental data, is usually intractable and sometimes follows a subjective trial-and-error procedure. For this, this paper presented a novel calibration methodology based on an optimization algorithm (particle swarm optimization (PSO)) for an advanced elastoplastic constitutive model. A multi-objective function was designed to adjust the global quality for both monotonic and cyclic triaxial simulations. To overcome computational problem probably appearing in simulation of the cyclic triaxial test, two interrupt mechanisms were designed to prevent the particles from wasting time in searching the unreasonable space of candidate solutions. The Dafalias model has been used as an example to demonstrate the main programme. With the calibrated parameters for the HN31 sand, the computed results were highly consistent with the laboratory experiments (including monotonic triaxial tests under different confining pressures and cyclic triaxial tests in two loading modes). Finally, an extension example is given for Ottawa sand F65, suggesting that the proposed platform is versatile and can be easily customized to meet different practical needs.

8th Ishihara lecture: Holistic evaluation of liquefaction response

Soil liquefaction during earthquakes is a highly dynamic process involving rapid development of excess pore water pressures (EPWP), reduction in soil stiffness and strength, and diffusion of EPWPs through water flow. In addition, the liquefaction response is characterized by strong cross-layer interactions that significantly influence the severity of liquefaction and overall system response of liquefying deposits. To emphasize the importance of dynamic interactions and provide an in-depth understanding of the liquefaction response, a framework for a holistic evaluation of the liquefaction response is presented. Three key aspects of the response are required to be concurrently considered in the holistic evaluation of the liquefaction response: element (soil) response, cross-layer interactions (system response) and intensity of the input motion. The proposed approach is applied to a comprehensive series of nonlinear dynamic analyses (NDAs) of well-documented case history sites from Christchurch, New Zealand, to identify key interaction mechanisms and quantify effects of dynamic interactions on the liquefaction response. As state-of-practice simplified liquefaction evaluation procedures ignore interactions within the deposit, results from simplified analyses substantially differ from those observed in NDA and show significant anomalies in the evolution of the liquefaction response throughout the depth of liquefiable deposits. A systematic approach for an NDA-based improvement of simplified analysis is proposed to incorporate interaction mechanisms and system response effects in simplified liquefaction evaluation procedures.

Grain Shape Effects on the Liquefaction Response of Geotextile-Reinforced Sands

Grain Shape Effects on the Liquefaction Response of Geotextile-Reinforced Sands

Energy-based assessment of cyclic liquefaction behavior of clean and silty sand under sustained initial stress conditions

In practical engineering, sand deposits containing some finer particles usually sustain an initial static shear stress. This study investigates the sustained initial stress effect on liquefaction response of saturated sand through conducting cyclic undrained triaxial tests. The obtained response of sand samples containing a small amount of silty fines is compared to that of clean sand under similar relative densities. The results exhibit that various stress conditions result in two response patterns named as cyclic mobility and residual deformation accumulation. It is shown that the addition of silty fines can either enhance or reduce the cyclic liquefaction resistance of sand, depending on the fines content, while the sustained initial stress plays a beneficial role in resisting cyclic failure for samples with or without the addition of fines under otherwise identical testing conditions. It is also found that the dissipated energy accumulated in both the silty and clean sand follows a power-law relationship to the generated residual pore pressure during cyclic loading. A unified relationship is further established between the liquefaction resistance and dissipated energy, which may be useful for developing an energy-based assessment of in-situ soils using strength data from laboratory experiments.

Pore-water pressure and liquefaction response of layered fine soils undergoing cementation

Cemented paste backfill (CPB) is fine-grained soil undergoing cementation. It is widely used in mining operations for ground support and tailings disposal. In the field, CPB may be placed in one layer (continuous filing), or multiple layers (discontinuous or sequential filling). Until now, no studies have addressed the effect of the different filling strategies on the CPB response during cyclic events by using the shaking table technique. This paper presents new findings regarding the effect of the different filling strategies of CPB on its geotechnical response to dynamic loading. Samples were prepared with different scenarios, including one layered-CPB sample (discontinuous filling), in which each layer was cured for a different duration, and two unlayered-CPB samples (continuous filling), one of which was cured for 2.5 h and the other for 4.0 h. All samples were exposed to the same cyclic loading conditions using a one-dimensional shaking table. Geotechnical parameters, including pore-water pressure, settlement, volumetric water content and liquefaction susceptibility, were monitored or determined before, during and after shaking. The results indicate that layered-CPB samples are resistant to liquefaction under the studied loading conditions, while the unlayered-CPB samples are prone to liquefaction under the studied conditions when they are cured for less than 4.0 h.

Experimental Studies and Constitutive Modeling of Static Liquefaction Instability in Sand–Clay Mixtures

This paper examines static liquefaction phenomena in sand–clay mixtures from both experimental and theoretical perspectives. Consolidated undrained triaxial tests (CU tests) are implemented on a mixture of sand and clay to study the effects of initial relative density, confining pressure, and clay content on static liquefaction responses. By using the equivalent granular state parameter, a state-dependent hardening plasticity model is proposed to reproduce mechanical responses, as well as to replicate the observed static liquefaction phenomenon. In accordance with the second-order work theory, the criteria for predicting the potential instability and static liquefaction of sand–clay mixtures are obtained. The analyses show that (1) static liquefaction is prone to be promoted by low initial relative density and confining pressure; (2) even a small amount of clay particles can significantly increase the liquefaction susceptibility in loose sand–clay mixtures; (3) the proposed constitutive model can provide a satisfactory match between the test data and the simulations; and (4) even when the state of the soil is potentially unstable, soils can still remain stable unless second-order work vanishes, which indicates the inception of static liquefaction.

Liquefaction responses of fibre reinforced sand in shaking table tests with a laminated shear stack

Mixing unidimensional tension-resistant elements into cohesionless soils, which is well known as fibre-reinforcement, is effective at strengthening the soils as well as increasing their liquefaction resistance in triaxial tests. In this study shaking table tests were performed on unreinforced and fibre reinforced sand models, contained in a laminated shear stack, to gather evidence as to whether or not the fibre reinforcement technology might reduce liquefaction susceptibility in a loading condition that has the semblance of an earthquake. The test results show that the excess pore pressures generated, and the amount by which the equivalent shear modulus is reduced, are significant in unreinforced and reinforced models when exposed to continuous sinoidal biaxial shaking simultaneously in horizontal and vertical directions. Fibre-reinforcement delays and reduces the build-up of excess pore pressures, slightly. Fibre-reinforcement also decreases slightly the attenuation of the acceleration amplitudes as well as the degradation of stiffness resulting from the generation of excess pore pressures. A constitutive model based on the rule of mixtures, which captures the load sharing between fibres, sand skeleton and pore water in triaxial loading conditions, and accounts for the anisotropy of the fibre orientation distribution, was modified and then used to study the shaking table deformation pattern. The stress the fibres impose on the sand skeleton in the vertical direction was determined and a new pore pressure ratio was used to assess whether or not liquefaction occurred. This enabled a mechanistic understanding of how the fibres alter the sand skeleton stresses and suppress liquefaction development. Liquefaction eventually occurred, or was close to occurring, in the reinforced model at different depths even though the fibres added stresses to the sand skeleton. The earth pressures prevailing in these 1 g shaking table tests were not sufficiently large for optimal interaction between fibres and sand skeleton. The fibres were not sufficiently tensioned as the confining (clamping) stresses provided by the neighbouring sand particles were not large enough. This means that the benefits of this reinforcement technology may be minor in practical situations where the fibre reinforced soil is at shallow depths.

DEM analysis of cyclic liquefaction behaviour of cemented sand

This study presents an investigation of cyclic liquefaction response of cemented sand using discrete element method (DEM). To reproduce the effect of cementation for cemented sand, an existing bond contact model was introduced in a DEM code, and then a series of undrained cyclic triaxial tests were simulated, where different cement contents (CCs) and cyclic stress ratios (CSRs) were considered. Finally, the evolutions of some important macro and micro-scale variables were analyzed. For cemented sand, if the CC is large or the CSR is small, few bond breakages occur, the mechanical coordination number almost remains unchanged, and the input work mainly contributes to the increase in the elastic energies at particle contacts and bond contacts, not leading to the onset of liquefaction. In the case of the liquefied cemented sand, with increasing CSR, bonds break more intensely, and the mechanical coordination number declines faster. The elastic energies at particle contacts and bond contacts tend to be zero faster, and the dissipated energies due to sliding friction, rolling rotation, and twisting rotation reach their maximum more promptly. In addition, the normal orientations for the bonded contacts, unbonded contacts, broken bond contacts, and total contacts, all tend to be isotropic more rapidly.

Evaluation of field sand liquefaction including partial drainage under low and high overburden using a generalized bounding surface model

The article presents simulations of the seismic liquefaction response of dense and loose clean Ottawa sand under low and high overburden in the centrifuge, using Program FLAC3D and the P2Psand constitutive model. P2Psand was initially calibrated in the paper with cyclic stress-controlled triaxial tests and then modified with information from two centrifuge experiments. The calibrated model was used to simulate four centrifuge tests covering relative densities from 45% to 80% and overburden pressures from about 100 kPa (∼1 atm) to 600 kPa (∼6 atm). The four numerical computations were fully coupled effective stress simulations that allowed for pore water pressure buildup and dissipation at every time step. The calibration yielded very good matches between numerical and experimental results in all four centrifuge experiments, and calibrated P2Psand input parameters are suggested for practitioners in similar clean sands. The simulations confirmed the increased diffusivity of the sand layer under high overburden obtained before from the centrifuge results. The reason is that P2Psand assumes that the sand bulk modulus is proportional to the square root of the mean effective stress, consistent with the similar conclusion derived from the centrifuge data by the authors. The calibrated P2Psand model was also used to perform “no flow” simulations of the same four centrifuge experiments, in which fluid flow was not allowed during or after shaking. No flow simulations are used sometimes in practice to reduce numerical effort, on the assumption that liquefaction in the field is mostly undrained. It was found that this assumption may produce useful engineering results for a low overburden of 1 atm, but it may become increasingly incorrect and too conservative at higher overburden. The reason is that for certain field conditions, fluid flow becomes more significant during shaking under high overburden due to increased sand diffusivity.

Combined effect of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands

Cyclic liquefaction of silty sands remains to be very intriguing for both research and practice. Even though many factors are known to influence the liquefaction resistance of sands, the effect of fines content is perhaps one of the most studied yet still a controversial one. Effect of grain size distribution by means of uniformity coefficient is also studied in literature but not as much as fines content influence. Moreover, to date, no clear relationship has been established between the uniformity coefficient and cyclic liquefaction resistance of clean or silty sands. This study adopts a distinct methodology by considering the effects of fines content and uniformity coefficient together, which were typically considered separately as two isolated parameters in previous studies (i.e., typically, only one of them was considered or focused). A series of constant volume cyclic direct simple shear (CDSS) tests were performed on mixtures of two base sands and four non-plastic silts at different fines contents, which also enabled authors to observe the liquefaction response of silty sands with different gradations. Based on the analysis, a new equation was developed which predicts the cyclic liquefaction resistance of silty sand by considering the uniformity coefficients of the sand (CUsand) and silt (CUsilt) fractions forming the soil together with its fines content (FC). The proposed equation was also demonstrated to work very well on six distinct silty sands having different gradations and fines contents from literature. The level of the combined influence of fines content and uniformity coefficient on cyclic liquefaction resistance of silty sands is also shown to be considerably affected by the magnitude of relative density. Practical implications and limitations of the new equation are discussed as well.