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The 2008 Mw7.9 Wenchuan earthquake in China caused widespread soil liquefaction and ground failures. A liquefaction case study of gently sloping ground at Yingxiu Town in the near-fault region is presented, which features its relatively thick deposits of sand-gravel mixtures, high soil stiffness, extremely intensive ground motion, large lateral spreading and severe damage of superstructure. The details of ground motion, site condition, field manifestations of liquefaction, subsurface soil profiles and field testing of shear wave velocities are presented. A conceptual binary mixture model is proposed to explain the gravel content effect on the stiffness and liquefaction resistance of gravelly soils. A preliminary liquefaction triggering evaluation method for gravelly soils is proposed by considering the gravel content correction of shear wave velocities based on the existing simplified procedure for typical sandy soils. The failure mechanism of the Baihua Bridge built at this site is explored, and the liquefaction-induced lateral spreading in down-slope direction might aggravate the failure process by imposing a large kinematic load on the piers besides the inertial forces transferred from the superstructure.

Liquefaction of silty sands remains puzzling due to the complexity involved in the interaction between coarse and fine particles during loading. This paper presents first-hand experimental data from a series of cyclic triaxial tests under controlled particle characteristics, with the aim to elucidate the influence of particle-size disparity on the liquefaction resistance of sand−fines mixtures. A detailed analysis of the test results and an experimental database compiled from the literature reveal that the particle-size disparity, defined as the ratio between the characteristic sizes of the base sand and the fines, is a major and rational factor controlling the reduction of cyclic resistance of sand−fines mixtures as compared with factors such as the grading and shape of the base sand. A simple, explicit expression is further proposed to properly account for the reduction of cyclic resistance of sand due to fines.

In dynamic centrifuge modelling, shaking control is one of the key technologies and has important effects on the accuracy and repeatability of the model tests. In this study, a series of analyses and experiments is performed to study the frequency response functions (FRFs) and shaking performance of the in-flight hydraulic shaker on a geotechnical centrifuge at Zhejiang University (i.e. ZJU-400). First, based on an analytical model of the bucket−shaker−container system with interaction with the servo-hydraulic system, parametric studies on the FRF were conducted to identify the key variables in shaking control. Then a suite of dynamic centrifuge model tests were conducted under different centrifugal accelerations, payloads and shaking amplitudes, to observe the FRFs between the command and the achieved accelerations at the table. The results reveal that FRF is affected by several factors including the shaking amplitude, model parameters and centrifugal acceleration, where the shaking amplitude is the dominant factor. The FRF cluster model of the shaker was established and a feed-forward control procedure is proposed to facilitate the possibility of well-controlled shaking with only one try. The validation model tests show that the proposed procedure secures a satisfactory accuracy of the waveform replication for both sine waves and earthquake motions.

This Data in Brief article provides summarized information of the liquefaction case histories from the 12 May 2008 Mw7.9 Wenchuan earthquake. According to the data processing procedures recommended in the related research article, all eighty-one case histories investigated by the present authors and seven other case histories from the literature are carefully compiled. All necessary information and the mean and standard deviation for some key parameters are given for these liquefaction case histories (i.e., site name, site location, site inclination angle, liquefaction manifestations, critical layer, soil sampling information, ground motion, total and effective stresses, shear-mass participation parameter, cyclic stress ratio (CSR) for Mw=7.5, normalized shear wave velocity (Vs1), data class and field testing time). These data may be used by colleagues to study the effect of gravel content on liquefaction behaviour of gravelly soils and develop the corresponding deterministic or probabilistic methods for liquefaction triggering evaluation.

The Liquefaction Experiments and Analysis Projects (LEAP) is an international effort to produce a set of high quality test data and to then use it in a validation exercise of existing computational models and simulation procedures for soil liquefaction analysis. A validation effort (LEAP-GWU 2015) was undertaken using a benchmark centrifuge model of a sloping deposit tested in a rigid-wall container. This article presents and discusses the shear stress-strain responses and effective stress paths of the LEAP-GW 2015 centrifuge tests and numerical predictions (including an assessment of the effects of the rigid boundaries).

A dynamic centrifuge model test of mildly sloping ground was conducted at Zhejiang University according to the LEAP-GWU-2015 experiment specifications. A 5-degree slope consisting of a saturated medium dense Ottawa F-65 sand was prepared by air pluviation method in rigid container, which simulated a prototype with a 20 m length and 4 m depth under 26 g centrifugal acceleration. The model was subjected to three smaller and two destructive motions. Test data and preliminary analyses of model responses during multiple shakings are presented. In-flight measurement of shear wave velocity by bender elements was used to characterize the evolution of soil state. Acceleration response spectra were presented and site amplification effects were observed. Shear stress-strain loops were calculated from acceleration records, and asymmetric dilatancy in the sloping ground was observed during liquefaction. Generation and dissipation of excess pore pressure were depicted. Large liquefaction-induced ground displacements were measured and analyzed. This study provides valuable data and delivers some important observations of liquefaction responses of a sloping ground.

Stone column is one of the prevailing liquefaction mitigation techniques to densify the surrounding soil, expedite the drainage and bring the possible shear reinforcement effect. The mitigation mechanisms of liquefaction triggering and the associated deformation of the improved ground have not been well explored yet, which hinders the development of robust design in engineering practices. Three centrifuge model tests, including a loose sand model, a dense sand model and a dense sand model with stone columns were conducted to explore the individual effect of densification and drainage caused by stone columns on seismic responses of a level silty sand ground, including the excess pore water pressure, acceleration and ground settlement, etc. The densification effect increases the dilatancy of the surrounding soil and hinders the generation of excess pore water pressure during shaking, thus significantly reduces the liquefaction potential and post-shaking settlement as well. However, it amplifies the upward propagating ground motion considerably. The drainage effect in a densified ground with SCs mainly takes place after shaking, and it accelerates the dissipation rate about 5–10 times that of a densified ground without SCs, which helps to quickly restore the ground stiffness and reduce the deformation to some extent. The contributions from the two effects to the post-shaking ground settlement were also observed and discussed. The present study provides insights on liquefaction mitigation mechanisms of the stone column-improved ground and valuable benchmark tests for further analysis.

Many submarine landslides occur through marine sensitive clay layers, and the strain softening behavior plays a key role. The changing soil properties induced by various disturbances will have marked impact on earthquake performance of submarine clay slopes. In the present study, undrained triaxial compression tests on reconsolidated samples of a soft sensitive marine clay were conducted, and a soil disturbance dependent simple constitutive model is proposed for describing post-peak nonlinear strain softening behavior of sensitive clays based on experimental results, and then is implemented in QUIVER code to perform one-dimensional seismic response analysis of mild infinite slopes, to address the relative importance of soil disturbance effect on the site response and sliding displacement of submerged slopes during seismic loading. Detailed laboratory test descriptions and results of a soft sensitive marine clay, model formulations and comprehensive computational efforts are presented. Parametric study of site response analysis focusing on the effects of soil disturbance degree and depth on generic clay grounds with varying sloping angles subjected to harmonic and earthquake loadings are performed. The predicted acceleration amplification, maximum shear strains and permanent displacements provide insight of earthquake performance of submarine sensitive clay slopes. The main findings are drawn based on several key concepts. First, undisturbed sensitive clay is typically stiffer and stronger than disturbed clay consolidated at the same stress level and hence, unless strain softening is triggered, structured sensitive clay will perform better than insensitive clay of the same residual strength. Second, post-peak softening at shallow depth will lead to strain localization on a thin layer, which is the main cause of sudden change of upward wave propagation characteristics and large permanent displacement at seabed surface of mild submarine clay slope. Thirdly, soil disturbance degrees and depths have very marked effects on seismic response and displacement performance of sensitive clay slopes, and such effect will be further enhanced by slope angle or earthquake intensity, which should be cautiously treated in engineering design.

Nonlinear site response of deep offshore clay deposit plays an important role in changing the characteristics of ground motions when subjected to strong shaking, especially when different amplification behaviors of acceleration and displacement are considered. The paper describes a series of centrifuge shaking table tests and numerical simulations to investigate the behavior of deep offshore clay deposits subjected to earthquake loadings. The centrifuge model tests were performed on a slightly overconsolidated clay deposit at UC Davis. A suite of shaking tests were conducted including impulse step wave testing, frequency sweeps, a small “elastic” earthquake event and a “ductility” level large earthquake event. Accelerations, displacements and pore pressures were measured in the soils (free field) throughout the test program. For the elastic level excitations, about a 33% amplification was observed between the input acceleration at the base and the measured accelerations near the top of the clay deposit. However, for the ductility-level earthquake excitation, which had peak input acceleration at the base of 0.46g, acceleration near the top of the deposit was reduced to 0.07g. These observations are correctly simulated by DEEPSOIL with proper soil models and parameters back analyzed from the centrifuge model test. Then systematic 1-D site response analyses are performed on synthetic clay deposit models with 30 to 120 m depths using the validated DEEPSOIL program, and the amplification characteristics of acceleration and deformation induced by base excitation with different intensities and frequencies are analyzed in both time and frequency domains. The results reveal that for deep soft offshore clay deposits subjected to large earthquakes, significant acceleration attenuation may occur near the top of deposit due to soil nonlinearity and even local shear failure; however, significant amplification of displacement at low frequencies is expected regardless of the intensities of base motions, which suggests that for displacement sensitive offshore foundations and structures, such amplified low-frequency displacement response will play an important role in seismic design.

The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance (CRR)-shear wave velocity (V s)-void ratio (e) of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V s of soil is raised high enough (i.e., no less than the critical velocity) to resist the given earthquake loading according to the CRR-V s relationship, and then this requirement is transferred to the control of target void ratio (i.e., the critical e) according to the V s-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V s-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.

Three dynamic centrifuge tests with different densities (corresponding to loose, medium dense, and dense deposits) were conducted at Zhejiang University for LEAP-UCD-2017 for an exercise of repeatability and reproducibility. The same model used in LEAP-GWU-2015 representing a 5-degree slope consisting of saturated Ottawa F-65 was repeated in 2017, but more rigorous protocols and new techniques (CPT and high-speed cameras) were included in Zhejiang University experiments. Test facilities and detailed modeling and testing procedures are presented; uncertainties in input parameters are also discussed. Preliminary results associated with selected experiment are presented.

The 2008 Wenchuan earthquake caused widespread liquefaction of gravelly soils (i.e., gravelly sands and sandy gravels), which phenomena show many differences compared to those of typical sands. To study the liquefaction mechanism and triggering evaluation of gravelly soils during this event, comprehensive case studies with measurement of shear wave velocity on both liquefied and non-liquefied sites were carried out according to a suite of recommended procedures for site investigation, field testing and data processing. Three typical cases were provided to illustrate the distinct characteristics of ground motion, liquefaction manifestation, soil profiles and field testing, and explore the possible mechanisms of liquefaction. Eighty-one well identified case histories were obtained, which feature the updated estimation of ground motion parameters from the USGS ShakeMap and the probabilistic treatment of the datasets. The preliminary analyses on liquefaction triggering boundary curves, shear wave velocities of these case histories and the applicability of the Ishihara criterion (1985) indicate that the gravel content plays a key role in the liquefaction mechanism and the consequences of gravelly soil deposits, and the liquefaction evaluation of gravelly sands and sandy gravels should be treated separately.

Cone penetrometers (CPTs) are commonly used for characterising the soil properties of centrifuge models; CPT data is useful for interpretation and quality control. This paper describes the development and design of a new robust CPT device for centrifuge testing. The new device consists of a 6mm cone, an outer sleeve, and an inner rod that transmits cone tip forces to a load cell above the ground surface. The design eliminates the need for a custom submerged strain gauge bridge near the tip, significantly reducing cost.A direct comparison was performed between this CPT device and another similar device developed at the University of Cambridge. CPT’s were manufactured using the new design and then shipped to eight different centrifuge facilities, for quality control of similar experiments performed for LEAP (Liquefaction Experiments and Analysis Projects). All the centrifuge tests simulated a 4 m deep deposit of soil, all consisting of Ottawa F-65 sand with relative densities ranging between about 45 to 80%. The results obtained have been extremely valuable as an independent assessment of the density calculated from mass and volume measurements at different laboratories.

Liquefaction-induced large deformations of shallow foundations were widely observed during strong earthquakes, and one important feature of these is that they occur relatively slowly compared to the duration of earthquake shaking. As most previous model tests used clean sands with high permeability, this type of “delayed” failure mode has not been observed or reproduced realistically in the laboratory to date. In this study, a dynamic centrifuge model test was performed under 30 g to study the mechanism of post-liquefaction progressive failure of buildings with shallow foundation on relatively thick deposits of liquefiable sandy soils. A two-dimensionally asymmetrical model structure was used to simulate the eccentric loads at the interface between the foundation and the subsoil. A clayey sand model with a relative density of 35% was prepared to have the relatively low permeability and coefficient of consolidation comparable to those of in-situ sandy soils. A prototype 2 Hz, 80 s long sine sweep with peak amplitude of 300 gal was used to simulate an earthquake strong enough to trigger a typical liquefaction state. Seismic responses in the liquefiable deposits and deformations of the structure were monitored during and after shaking. The main finding of this study is that the post-liquefaction progressive failure of shallow foundation was due to the large ground deformation of subsoil where significant shear strain localization had developed during liquefaction. Progressive settlement and tilting of shallow foundation will continue as long as the liquefaction state maintains, and longer durations of liquefaction lead to larger deformations.

The development of physical modeling for mega engineering prototypes requires sophisticated use of the capability of current centrifuge facilities. In this study, centrifuge model tests were performed to investigate the dynamic response of high fill slope by using generalized scaling law in an improved way. Firstly the two-stage generalized scaling law was partly re-organized by considering the separate similitude of dynamic strain for the virtual 1 g field, to solve the inherent problem of the scaling of soil strain when the derived prototype strain exceeded some important thresholds. Then a series of centrifuge model tests were conducted under different centrifugal accelerations to model a high fill slope with a prototype height of 100 m by the approach of “modeling of models”. Dynamic responses under sine waves with different amplitudes were monitored and the re-organized generalized scaling law was validated for nonlinear dynamic response with shear strain less than 1%. It was observed that site amplification of high fill slope was affected by both soil nonlinearity and soil strata non-uniformity, where soil nonlinearity led to smaller acceleration amplification under stronger excitation and soil strata non-uniformity contributed to the acceleration de-amplification and larger displacement amplification at the weak sublayer. The large dynamic displacement near the slope surface consequently contributes to the development of lateral cracks after strong shaking. Seismic response under earthquake motions revealed that high fill slope with inclined non-uniform strata was characterized by multiple vibration modes and lower fundamental frequency, which was more vulnerable to earthquake motions with abundant frequency components. This study provides a more physically meaningful use of the similitude of dynamic stress-strain relation in centrifuge modeling for large-scale geotechnical problems under dynamic loadings.

In-flight measurement of shear-wave velocity (Vs) in centrifuge model test is important for real-time characterization and has multiple engineering applications. Accurate measurement of Vs by bender elements (BE) in centrifuge models is still challenging, in part because of the curved raypath of shear-wave propagation. By focusing on the variable g-fields inside the models, this paper provides new equations with improved Vs-depth function to raypaths of shear waves for two typical centrifuge model setups. Parametric analyses including the centrifuge specifications, testing layout, and soil characteristics were carried out to study their effects on raypaths and Vs accuracy. The results show that testing layout has significant effect on Vs accuracy whereas soil characteristics have considerable effect. Variable g-fields will cause a further reduction of Vs accuracy, which is dominated by centrifuge radius. To secure an accurate Vs measurement in centrifuges, it is recommended that Di/L should be lar...

Liquefaction of granular soil deposits is one of the major causes of loss resulting from earthquakes. The accuracy of the liquefaction potential assessment at a site affects the safety and economy of an engineering project. Although shear-wave velocity ( Vs ) -based methods have become prevailing, very few works have addressed the problem of the reliability of various relationships between liquefaction resistance (CRR) and Vs used in practices. In this paper, both cyclic triaxial and dynamic centrifuge model tests were performed on saturated Silica sand No. 8 with Vs measurements using bender elements to investigate the reliability of the CRR- Vs1 correlation previously proposed by the authors. The test results show that the semiempirical CRR- Vs1 curve derived from laboratory liquefaction test of Silica sand No. 8 can accurately classify the ( CRR, Vs1 ) database produced by dynamic centrifuge test of the same sand, while other existing correlations based on various sandy soils will significantly under o...

Dynamic centrifuge model test was conducted to study the earthquake-induced differential settlement of foundation on cohesive ground, and the influence of asymmetry of building was investigated. During the experiment, the overconsolidated kaolin clay ground with a three-dimensional asymmetrical structure model was shaken by a basically balanced input motion, and bender elements were used to measure shear wave velocities of model ground to reveal the soil fabric evolution during and after shaking. The test results show that, the total seismic settlement of foundation is composed of instantaneous and long-term post-earthquake settlements, and most of the differential settlement occurs immediately after the earthquake while the post-earthquake settlement is relatively uniform despite its large amplitude. The asymmetry of building affects the settlement behavior considerably. Compared with 1-or 2-dimensional structures, more evident differential settlement occurs under three-dimensional asymmetrical building during shaking, which accounts for one-half of the total seismic settlements and results in complex spatial tilting effects of foundation.

The great Wenchuan earthquake (M s = 8.0) in 2008 caused severe damage in the western part of the Chengdu Plain. Soil liquefaction was one of the major causes of damage in the plain areas, and proper evaluation of liquefaction potential is important in the definition of the seismic hazard facing a given region and post-earthquake reconstruction. In this paper, a simplified procedure is proposed for liquefaction assessment of sandy deposits using shear wave velocity (V s), and soil liquefaction from the Banqiao School site was preliminarily investigated after the earthquake. Boreholes were made at the site and shear wave velocities were measured both by SASW and down-hole methods. Based on the in-situ soil information and V s profiles, the liquefaction potential of this site was evaluated. The results are reasonably consistent with the actual field behavior observed after the earthquake, indicating that the proposed procedure is effective. The possible effects of gravel and fines contents on liquefaction of sandy soils were also briefly discussed.

The bender element testing features its in-plane directivity, which allows using bender elements to measure the shear wave velocities in a wider range of in-plane configurations besides the standard tip-to-tip alignment. This paper proposed a novel bender element testing technique for measuring the horizontal shear wave velocity of soils, where the bender elements are surfacemounted and the axes of the source and receiver elements are parallel to each other. The preliminary tests performed on model ground of silica sand showed that, by properly determining the travel distance and time of the shear waves, the surface-mounted bender elements can perform as accurately as the conventional “tip-to-tip” configuration. Potentially, the present system provides a promising nondestructive tool for characterizing geomaterials and site conditions both in laboratory and in the fields.

Shear wave velocity ( Vs ) offers engineers a promising alternative tool to evaluate liquefaction resistance of sandy soils, and the lack of sufficient in-situ databases makes controlled laboratory study very important. In this study, semitheoretical considerations were first given based on review of previous liquefaction studies, which predicted a possible relationship between laboratory cyclic resistance ratio ( CRRtx ) and Vs normalized with respect to the minimum void ratio, confining stress and exponent n of Hardin equation. Undrained cyclic triaxial tests were then performed on three reconstituted sands with Vs measured by bender elements, which verified this soil-type-dependent relationship. Further investigation on similar laboratory studies resulted in a database of 291 sets of data from 34 types of sandy soils, based on which the correlation between liquefaction resistance and Vs was established statistically and further converted to equivalent field conditions with well-defined parameters, reve...

Recent studies using field case history data yielded new criteria for evaluating liquefaction potential in saturated granular deposits based on in situ, stress-corrected shear wave velocity. However, the conditions of relatively insufficient case histories and limited site conditions in this approach call for additional data to more reliably define liquefaction resistance as a function of shear wave velocity. In this study, a series of undrained cyclic triaxial tests were conducted on saturated sand with shear wave velocityVs measured by bender element. By normalizing the data with respect to minimum void ratio, the test results, incorporated with previously published laboratory data, statistically revealed good correlation of cyclic shear strength with small-strain shear modulus for sandy soils, which is almost irrespective of soil types and confining pressures. The consequently determined cyclic resistance ratio,CRR, was found to be approximately proportional toV s 4 . Liquefaction resistance boundary curves were established by applying this relationship and compared to liquefaction criteria derived from seismic field measurements. Although in the range ofVs1>200 m/s the presented curves are moderately conservative, they are remarkably consistent with the published field performance criteria on the whole.

Small strain shear modulus G max is a key parameter together with the state of stress and shear strain amplitude for predicting the dynamic behavior of soils. Although the seismic cyclic loading on saturated soil deposits induces a decrease in effective stress and a rearrangement of the soil skeleton which may both lead to a degradation in undrained stiffness and strength of soils, only the contribution of effective stress reduction to G max degradation is considered in the Hardin and Richart equation which is widely used in seismic response analysis nowadays, and that of soil fabric change is neglected. In this paper, undrained cyclic triaxial tests were conducted on normally and isotropically consolidated saturated sands with the shear wave velocity measured intermittently by bender element during cyclic liquefaction, to study the influences of seismic cyclic loading history on small strain shear modulus G max during earthquake. And the G max values of samples without such influences were investigated for comparison. The tests results indicate that G max of sand under high amplitude seismic cyclic loading history influences is moderately lower than the corresponding value of non-cyclic loading effects at the same effective stress. Hence it is necessary to reinvestigate the determination of G max in seismic response analysis carefully to predict the ground responses more reasonably.

In order to study the seismic responses of saturated sand, a group of centrifuge-shaking table tests on saturated medium dense sand and dense sand are conducted at the institute of technology, SHIMIZU Corporation in Japan. Then finite difference software FLAC/FLAC3D is used to calibrate the experimental results. Ideal elastic-plastic model, Mohr-Coulomb's criterion and Finn's pore pressure generation model are used in the simulation. The effect of confining pressure on relative density, soil shear modulus, bulk modulus and pore pressure generation parameters are considered. Influence of saturation is also taken into account. With comparison, the numerical results show good agreement with those of the centrifuge tests and basically reveal the development law of pore pressure and acceleration. The feasible numerical model lays a good foundation for the liquefaction analysis in more complicated conditions.

Nowadays, several geotechnical centrifuges are newly developing for different purposes in China (Hou et al. 2006). One of them (Ma et al. 2006) introduced the development of a 150 g.ton centrifuge in Tongji University, which was designed to study geotechnical problems in soft ground. In this year, a large centrifuge with a payload capacity of 400 g.ton, termed ZJU-400, was installed in Zhejiang University, Hangzhou, PR China. It is anticipated that the facility will contribute greatly to theoretical and practical research in the fields of geoenvironmental engineering, soil dynamics and earthquake engineering and foundation engineering. The centrifuge facility will become an important part of the Key Laboratory of Soft Soils and Geoenvironmental Engineering, Ministry of Education, Zhejiang University. Table 1 lists some centrifuges in mainland China which have capacities larger than 100 g.ton.

Quality control of ground improvement is a difficult but very important aspect of liquefaction mitigation construction. In this paper, an approach to evaluate the improvement level in liquefiable soils treated by stone columns was developed based on the liquefaction resistance-shear wave velocity-void ratio correlations of sandy soils. According to this method, the required level of ground improvement is supposed to be obtained once the target velocity is reached for a given earthquake magnitude, and this requirement will transfer to the void ratio control during stone column installation. A case study using vibro-stone column is introduced, where field tests including seismic testing (SASW) and SPT were performed before and after ground treatment, and the effectiveness of stone columns for liquefaction mitigation was properly evaluated by shear wave velocity. The high consistency between Vs- based and SPT-N value-based evaluations indicates that shear wave velocity could be used to develop criteria for ground improvement needed to mitigate liquefaction.