Onset Of Liquefaction Research Articles

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.

Numerical investigation of dynamic soil response around a submerged rubble mound breakwater: II. Loose sandy seabed

Low-crested structures such as submerged rubble mound breakwaters (RMB) are commonly used as successful examples of coastal protection measures. This study addresses foundation issues related to the performance of a submerged RMB constructed on a liquefiable site where the foundation soils have been loosely deposited; these issues were investigated using an integrated numerical model proposed by Zhao et al. (2018). Unlike previous work in Zhao et al. (2018), the dynamic features of loose sand deposits (i.e. build-up of pore water pressures, development of plastic strains, degradation of soil stiffness) due to the fluid–seabed-structure interactions, accompanied by the onset of liquefaction, were simulated. The reliability of this model to predict the liquefaction susceptibility of loose sand deposits was validated against the experimental results available in literature. This study shows that the submerged RMB constructed on a liquefiable seabed experienced progressive and asymmetric downward settlement under successive loading cycles. The opposing currents in the wave field tended to enhance this asymmetric settlement whereas the following currents did the opposite. Regardless of changes to the magnitude and direction of current velocities, ignoring the currents in the wave field may lead to an overestimation of the increased rate of residual pore water pressures in the region underneath the breakwater, particularly in shallow soil layers where the maximum relative differences can reach up to 120% of (p̄current−p̄no-current)∕P0 at t∕T=25.

A multilateral analysis of slope failure due to liquefaction-induced lateral deformation using shaking table tests

Liquefaction-induced lateral displacement can cause substantial deformations and trigger failure in the saturated sandy slopes. This study elaborates on the results of a shaking table experiment performed on a saturated sandy slope model. A transparent Plexiglass container was used to allow visualization of the time-dependent ground displacements at different grid points. Using colored sand grid along with the video-tracking analysis technique provided an excellent opportunity for instant monitoring of the model deformation in both the time and space domains. Furthermore, the pore pressure buildup and dissipation in the soil medium and acceleration time histories of the model were recorded and analyzed. Detailed and comprehensive analyses of the high-resolution recorded data streams resulted in the determination of the onset of liquefaction and the induced subsidence, acceleration response, deformation behavior, and shear strain progress through time and depth at different slope sections. It was also found that the shear strain rate was different in the on-slope and free field locations, and its value was proportional to the liquefaction duration. It was also observed that the variation of the shear strain rate at different depths in the free field led to a localized sliding event.

Estimation of Transient Forces in Single Pile Embedded in Liquefiable Soil

Abstract During the transient phase of liquefaction, i.e., from the onset of liquefaction to the stage of full liquefaction of soil, intrinsic properties of a soil–pile–structure system change caus...

Evaluation of the effects of initial deviatoric stress and cyclic stress amplitude on liquefaction potential of loose and medium-dense sands: An energy-based method

The energy-based method is a promising tool for evaluating soil liquefaction potential. In this study, the effects of initial deviatoric stress (qs) and cyclic stress amplitude (qcyc) on soil liquefaction potential in undrained cyclic triaxial tests were evaluated using the energy-based method. The testing results indicate that the required dissipated energy for the onset of liquefaction is influenced by both qcyc and qs for a loose sand, while it is only affected by qs for a medium-dense sand. For both loose and medium-dense sands, there exists an approximately unique relationship between the residual excess pore water pressure ratio and the normalized dissipated energy (Wn) during cyclic loadings, independent of qcyc and qs. The relationship between the double-amplitude axial strain and the Wn is influenced not only by initial conditions but also by loading conditions. The evaluation of the effects of the various factors on the liquefaction potential based on the energy-based method provides insight into the liquefaction resistance for both loose and medium-dense sands.

Liquefaction Potential Assessment of Brahmaputra Sand Based on Regular and Irregular Excitations Using Stress-Controlled Cyclic Triaxial Test

The response of saturated soil during earthquakes is governed by many factors such as frequency content, strain, stress, excess pore-water pressure and strength variations within the soil mass. This paper highlights the effect of strains on the stiffness modulus and its degradation at the liquefied condition of cohesionless soil. Cyclic triaxial (CT) tests, in stress-controlled manner, were carried out on saturated sandy soil specimens made at different relative density (Dr = 30%–90%) and effective stress (σ′c = 50–200 kPa). The reconstituted specimens were subjected to regular and irregular stress histories. Representative strong motions with varying PGA were chosen, and the corresponding irregular stress histories were used. Additionally, regular stress histories constituted from different cyclic stress amplitudes were also used. The responses of the saturated specimen were obtained in terms of the excess pore-water pressure generation and strain accumulation with elapsed time. In comparison to the standard frequency and duration parameters (namely the predominant period and significant durations), it is observed that the responses are more influenced by Arias intensity and specific energy density of the strong motion. Based on the increase in pore-water pressure, reduction in shear modulus and increase in shear strain within the specimens, the complete manifestation of liquefaction is divided in four zones, namely the no liquefaction zone, quasi-liquefaction zone, zone marking the onset of liquefaction and the completely liquefied zone. The criteria for the onset of liquefaction of Brahmaputra sand involving shear strain, peak ground acceleration and cyclic stress ratio are provided.

Assessment of Dynamic Response of Cohesionless Soil Using Strain-Controlled and Stress-Controlled Cyclic Triaxial Tests

Soils subjected to earthquake motions undergo random variations in stress, strain and frequency during the entire period of shaking. The spatial and temporal complexity of the strong motions is commonly addressed through simplistic strain-controlled or stress-controlled cyclic loading tests as a part of laboratory investigations. Such a methodology is utilized and reported in the present study for assessing the dynamic response of cohesionless sand obtained from River Brahmaputra, India. In order to assess the dynamic response and liquefaction potential of the cohesionless Brahmaputra sand, both stress-controlled and strain-controlled cyclic triaxial tests were performed on reconstituted cylindrical specimens prepared at different relative densities (Dr) ranging from 30 to 90%. The specimens were subjected to varying effective confining pressures (σ′c: 50–200 kPa), shear strain amplitudes (γ: 0.015–4.5%) and cyclic stress ratios (CSR: 0.05–0.3). For all the tests, the frequency of the applied harmonic loading was maintained at 1 Hz. The magnitude of excess pore-water pressure (PWP) generated during successive loading cycles of the strain-controlled tests was found to be considerably lower than that generated in a stress-controlled test. The strain-controlled test reveals a reduction in the development of excess PWP with the increase in confining pressure and relative density, thereby indicating a decrease in liquefaction potential with increasing confining pressure. The stress-controlled test highlighted that based on a particular CSR, an increase in confining pressure results in the requirement of higher deviatoric stress and smaller numbers of cycles are required to initiate liquefaction. Although apparently misleading, it is imperative that during earthquake, same deviatoric stress is applied on the entire soil deposit. Thus, for specimens at larger depths having higher confining pressure, the CSR value is smaller, and thereby successive deeper layers require more number of stress cycles to liquefy. Hence, the study revealed that both stress-controlled and strain-controlled tests can be successfully used to assess the dynamic properties and liquefaction potential of cohesionless specimens. Based on the findings, the developed cyclic shear stress ratio (CSR) = 0.5 and cyclic shear strain amplitude (γ) = 0.5% are considered as the limiting conditions to achieve the onset of liquefaction through strain-controlled and stress-controlled approaches, respectively.

Applicability of Pseudoprobabilistic Method of Liquefaction Hazard Assessment for Nuclear Power Plants at Diffuse Seismicity Sites

For the new nuclear power plants, the hazard of liquefaction due to earthquakes should be excluded by appropriate site selection or eliminated by engineering measures. An important question is how to define a quantitative criterion for negligibility of the liquefaction hazard. In the case of operating plants, liquefaction can be revealed as a beyond-design-basis event. It is important to learn whether the liquefaction hazard has a safety relevance and whether there is a sufficient margin to the onset of liquefaction. The use of pseudoprobabilistic method would be practicable for the definition of probability of liquefaction, but it could result in overconservative results. In this paper, the applicability of the pseudoprobabilistic procedure is demonstrated for the sites in diffuse seismicity environment and for low hazard levels that are typical for nuclear safety considerations. Use of the procedure is demonstrated in a case study with realistic site-plant parameters.

Liquefaction induced by deep vertical vibratory compaction

Three case histories were analysed where three different methods of deep vertical vibratory compaction were used to treat loose, water-saturated sand. Vertically oscillating probes not only generate cylindrical waves with strong ground vibrations that cause compaction of the soil but may also result in liquefaction. Cone penetration tests (CPTs) were performed before and after treatment to evaluate the compaction effect. Soil liquefaction could be observed on all sites during the start of deep vibratory compaction. On two sites, the onset of liquefaction could be documented by vibration measurements. A conventional CPT-based liquefaction analysis was performed, which suggested that liquefaction could be expected at all sites. The case histories analysed in this study suggest that vertically oscillating probes have the potential of being used as full-scale liquefaction testing machines. A new concept is outlined that could be used to establish the liquefaction hazard at a particular site.

A numerical study of particle friction and initial state effects on the liquefaction of granular assemblies

Liquefaction of sandy soil due to cyclic loading can result in catastrophic damage to the built environment. Liquefaction has been previously studied through field testing, laboratory experiments, and numerical simulations. However, the particle-scale behavior of granular materials during the initiation of liquefaction has not been comprehensively quantified. In the current work, the discrete element method is employed to study the effect of global void ratio, initial confining stress, overconsolidation ratio, and particle friction on liquefaction resistance. Mechanical coordination number, local void ratio distribution (LVRD) entropy, fabric anisotropy and average rotational velocity are quantified in each assembly to provide insight into the particle-scale physics governing liquefaction resistance. Results show that lower global void ratio, increased confining stress, higher OCR values, and higher particle friction all increase liquefaction resistance. Immediately prior to the onset of liquefaction, the mechanical coordination number in each assembly sharply decreased to approximately 2.5, with the remaining contacts attributed primarily to particle collision after liquefaction initiation and fabric collapse. Anisotropy induced in the cyclic loading process was due to normal contact force anisotropy, which was more prominent in the specimens with higher initial confining pressures. Liquefaction resistance for overconsolidated specimens was found to be lower than that of normally consolidated specimens at the same void ratio. We observe liquefaction resistance to be sensitive to the coefficient of interparticle sliding friction, especially for lower friction coefficients. Average particle rotational velocities are shown to increase with increasing interparticle friction. The quantity of energy dissipated through frictional sliding was controlled by both the rate of dissipation and the number of loading cycles to liquefaction. In sum, the simulations elucidate significant connections between micromechanical properties and liquefaction response at different initial states and with different particle frictions.

Equivalent linear computation of response spectra for liquefiable sites: The spectral interpolation method

A simplified methodology is presented for the computation of elastic response spectra at liquefiable sites, based on the widely used equivalent linear site response analysis method. The target response spectrum is obtained by frequency dependent interpolation between the response spectra for “non-liquefied” and for “liquefied” ground, the former computed for the native soil properties, without excess pore pressure buildup, and the latter for the properties of the liquefied soil. Apart from the structural frequency, the interpolation coefficient is also related to the factor of safety against liquefaction. In this way, the proposed methodology takes indirectly into account the initial segment of the seismic excitation time-history, until the onset of liquefaction, which is of cornerstone importance for the overall ground response at sites with low and moderate liquefaction potential. Results of parametric nonlinear numerical analyses and three field case studies are used to calibrate the methodology and evaluate its accuracy. In addition, the potential of the proposed methodology for defining code-oriented design spectra for liquefiable sites is examined.

Identification of transient vibration characteristics of pile-group models during liquefaction using wavelet transform

A time–frequency approach based on the wavelet transform is used to examine the transient vibration characteristics of two 2 × 2 pile-group models tested in a shake table. The models are subjected to three different records consisting of white noise input and two differently scaled records from the 2011 Christchurch Earthquake. In contrast to conventional Fourier analysis, the proposed method has the advantage of enabling the visualisation of the temporal variation in structural frequencies and frequency content of ground motion due to liquefaction in an effective way. It is found that liquefaction causes a decrease in structural frequency, whose reduction depends on the rate of excess pore pressure build-up, whereby high rates (“fast liquefaction”) lead to greater reduction, ie, up to 51%. Liquefaction is also responsible for the elongation of the predominant period of the ground motion and narrowing of its overall frequency bandwidth. The combined effect of reduction in structural frequency and filtering of high frequency components of the ground motion may lead to moving resonance condition, resulting in amplification of structural response. After the onset of liquefaction, there is a redistribution of maximum bending moment toward deeper elevations, indicating that kinematic soil-structure interaction dominates the overall seismic response.

Energy-based evaluation of liquefaction of fiber-reinforced sand using cyclic triaxial testing

The present study reviews a series of cyclic triaxial tests to investigate the liquefaction characteristics of Babolsar sand reinforced with randomly distributed fibers using an energy-based approach. The effect of fiber content, fiber length, confining pressure, and relative density were studied. The test results revealed that the addition of fibers increased the number of cycles required to liquefaction, resulting in higher cumulative dissipated energy. This accounted for the higher cyclic shear resistance of reinforced sand compared to unreinforced sand. Capacity energy is defined as cumulative dissipated energy to onset of liquefaction. The test results showed that Wliq was significantly affected by the fiber inclusion. Comparative studies demonstrated that energy-based method is a good way to evaluate liquefaction potential of fiber-reinforced sands.

Multi-directional modeling for prediction of fabric anisotropy in sand liquefaction

Anisotropy in the onset of liquefaction and post liquefaction under cyclic loading condition causes the change in response behavior of the soil. The proposed model operates within the integration of sliding/opening/closing framework of 17 predefined planes as local deformation. This leads to the use of better stress/strain multilaminate histories with many directional effects on soil behavior specifically internal mechanism during pre and post-liquefaction. The ability of multilaminate model for fabric anisotropy has been proven by comparison with the experimental results under drain and undrained conditions and monotonic and cyclic loading. The effects of induced anisotropy was also investigated.

Nickel ore bulk liquefaction a handymax incident and response

Nickel ore liquefaction has a direct correlation between the parameters of moisture content (MC) within the cargo and the response motion of the ship steering through its encountering weather condition at seas. The focus parameter of the potential onset of liquefaction is the amount of moisture content within the cargo. Therefore, having a moisture content below the transportable moisture limit (TML) before loading is the suggested mandatory standard of IMSBC11International Maritime Solid Bulk Cargoes. code for the transport of solid bulk cargoes which may liquefy. When cargo with an unsuitable/unsafe moisture content exceeding the threshold of its transportable moisture limit is loaded on board, ship's vibration and motion at sea may result in liquefaction taking place. In the worst case, the ship may develop a severe list due to cargo shift and capsize. Understanding that there is an inadequacy of scientific research works on the subject of remediation effort in liquefaction at seas and availability of closed form solution in this discipline. A response plan developed for a handymax bulk carrier liquefaction incident, with the objective to reduce the risk of capsizing and reclaim its stability by redistributing her homogeneous stowage loading on board into alternate loading is presented herein for information.

Equivalent Linear Computation of Response Spectra for Liquefiable Sites: The Spectral Envelope Method

AbstractA simplified methodology is proposed for the computation of elastic response spectra at liquefiable sites, based on the widely used equivalent linear (frequency domain) site response analysis method. The actual response spectrum is obtained as the upper-bound envelope of the thus calculated response spectra corresponding to the preliquefaction and the postliquefaction segments of the seismic excitation, the former computed for the natural soil properties and the latter for the properties of the liquefied soil. The time of liquefaction onset, which separates the two seismic excitation segments, is defined in terms of the minimum factor of safety against liquefaction within the liquefiable layer. Additional guidelines are provided for the estimation of the excess pore pressure buildup and the associated soil softening during the preliquefaction segment of the seismic excitation, as well as for the definition of the liquefied soil stiffness and the hysteretic damping ratio. The proposed methodology h...

Major advances in liquefaction research by laboratory tests compared with in situ behavior

Major advances in liquefaction research in the laboratory to understand the basic mechanisms in comparison with in situ behavior during previous earthquakes are reviewed. Then, several issues related to liquefaction triggering and post-liquefaction deformation are selected for further discussion in the author's perspective. These include effects of fines associated with aging, effects of gravels, effects of initial shear stress, and lateral spreading and lateral flow due to void redistribution. It has been disclosed that a quite a few issues still remain to be settled in evaluating liquefaction onset and post-liquefaction deformations for improving engineering design, particularly for Performance-Based Design (PBD).

Laboratory Study on Pore Pressure Generation and Liquefaction of Low-Plasticity Silty Sandy Soils during the 2012 Earthquake in Italy

AbstractThis paper describes the results of a laboratory investigation performed on clean sand and low-plasticity silty sands, recovered at different locations of the bank stretch at Scortichino, which was affected by serious damages following the 2012 Emilia Romagna earthquake in Italy. A comprehensive cyclic simple shear (CSS) testing program was undertaken to evaluate the liquefaction potential and pore pressure response of silty sand layers, which form the subsoil at the site. A series of undrained CSS tests were carried out on undisturbed samples by applying an initial static driving shear stress before cyclic loading (nonsymmetrical tests), with the aim of gaining a better understanding of the role played by a static preshearing on the observed liquefaction phenomena. The results obtained prove that, in nonsymmetrical cyclic loading tests, low-plasticity silty sands tend to be more susceptible to liquefaction than in symmetrical cyclic loading tests. The onset of liquefaction occurs by large shear s...

Correlation between liquefaction resistance and shear wave velocity of granular soils: a micromechanical perspective

The shear wave velocity method has become an increasingly popular means to evaluate the liquefaction potential of granular soils. Understanding the fundamental mechanism underlying existing empirical or semi-empirical relationships is important for better assessing their reliability. This paper presents a particle-scale study of the correlation between cyclic resistance ratio (CRR) and the shear wave velocity corrected for overburden stress (Vs1). The discrete-element method was used to simulate a series of undrained stress-controlled cyclic triaxial tests together with shear wave velocity (Vs) measurements. Discrete-element method modelling with various relative densities, confining pressures and micro-parameters was performed under various cyclic stress ratios (CSRs), and the onset of liquefaction was illustrated through both macroscopic and microscopic responses, for example, inferred excess pore-water pressure, mechanical coordination number and redundancy index. The inter-particle friction was identified as the key micro-parameter that governs the liquefaction resistance of granular soils. A micro-scale CRR–Vs1correlation considering two independent micro-parameters, inter-particle friction and particle shear modulus, was then obtained and further validated with the outcomes from three dynamic centrifuge model tests performed on silica sand no. 8. This study demonstrates that the CRR–Vs1correlation is particle specific, thus soil specific, and the particle mechanical properties should be included in the Vs-based method for future liquefaction evaluation of granular soils.

Influence of the void ratio and the confining on the static liquefaction in slopes in shangi sand

Se presenta un estudio numérico del inicio de la licuación estática en taludes, bajo condiciones no drenadas de carga, basado en un criterio de inestabilidad general para suelos elastoplás-ticos, fundamentado en el concepto de pérdida de controlabilidad. Se aplica el criterio al caso de carga axisimétrica, para detectar el punto de inicio de licuación con un modelo elastoplástico para arenas. Se comparan los resultados numéricos con evidencia experimental, encontrando un buen nivel de concordancia. Se presenta un estudio cuantitativo de la influencia de la presión media, relación de vacíos y la anisotropía inicial de esfuerzos sobre el inicio de la licuación en la arena de Changi. Se concluye que: a) el ángulo de fricción movilizado al inicio de la licuación no es una propiedad del material, sino que es una variable de estado; b) a pesar de las múltiples variables involucradas en el proceso de generación de inestabilidad no drenada, el estado de esfuerzos en el inicio de la licuación estática se puede representar convenientemente por una relación lineal entre Aq/p0 y r|0. Esta representación gráfica se puede usar en la práctica de la ingeniería geotécnica para cuantificar un margen de seguridad contra licuación estática de un talud arenoso.