Liquefaction Resistance Research Articles

Effects of partial saturation on the liquefaction resistance of sand and silty sand from Christchurch

The liquefaction resistance of partially saturated soil was experimentally investigated for one clean sand and one silty sand collected from a site in Christchurch, in an area severely affected by liquefaction in the 2010–2011 Canterbury earthquakes. A series of cyclic undrained tests were performed on fully and partially saturated sand and silty sand specimens, in conjunction with evaluation of saturation conditions in situ based on comprehensive field measurements of P-wave velocity (Vp) in Christchurch deposits. The Skempton’s B-value and P-wave velocity were comparatively used as measures for partial saturation in the laboratory. B-value - Vp relationships from the test results indicate that Vp steadily increases with the B-value until a threshold B-value is reached beyond which Vp remains unchanged at values indicating full saturation, i.e. Vp ;≥ ;1600 ;m/s. In general, the liquefaction resistance of tested sand and silty sand increases with a decrease in the B-value or Vp, i.e. with a reduction in the degree of saturation. Furthermore, test results suggest existence of threshold B-values and Vp for tested soils beyond which no significant increase in the liquefaction resistance was observed. This threshold B-values and Vp were found to be dependent on soil type and applied confining stress. The effects of partial saturation on liquefaction strength are different for the sand and silty sand when using Vp as a measure for the degree of saturation. While a gradual rate of increase in liquefaction strength with decreasing Vp is observed for the tested sand, the liquefaction strength of silty sand shows similar gradual increase with a decrease in Vp up to about 800 ;m/s, which is then followed by an abrupt increase in the liquefaction strength for Vp ;< ;800 ;m/s. Generally good agreement between liquefaction strength of tested soils and published data was observed, with a clear distinctive feature in the behaviour of the silty sand as compared to clean sands.

An extended hypoplastic model for sands with additions of highly plastic fines formulated under the ISA framework

In the present work, the hypoplastic model for sands by Wolffersdorff, (1996) coupled with Intergranular Strain Anisotropy (ISA) by Fuentes et al., (2020) is extended to account for the influence of fines content on the undrained cyclic response and liquefaction resistance of the material. A set of undrained cyclic triaxial tests on clean Ottawa C778 sand and on the same sand with additions of bentonite or laponite were simulated to evaluate the model’s capabilities. The comparison between experiments and element test simulation results suggest that the proposed extended model is able to accurately describe the behavior of clean Ottawa C778 sand and the significant influence of plastic fines in the response of the mixtures, such as the reduction in the accumulation rates of strains and pore water pressure under cyclic loading, and therefore, the improvement in the liquefaction resistance with increasing fines content.

Effects of pre-shearing and pre-consolidation histories on liquefaction behaviour of saturated loose sand: DEM investigation

PurposeThe study aims to investigate the effects of pre-loading histories (pre-shearing and pre-consolidation) on the liquefaction behaviour of saturated loose sand via discrete element method (DEM) simulations.Design/methodology/approachThe pre-shearing history is mimicked under drained conditions (triaxial compression) with different pre-shearing strain levels ranging from 0% to 2%. The pre-consolidation history is mimicked by increasing the isotropic compression to different levels ranging from 100 kPa to 300 kPa. The macroscopic and microscopic behaviours are analysed and compared.FindingsTemporary liquefaction, or quasi-steady state (QSS), is observed in most samples. A higher pre-shearing or pre-consolidation level can provide higher liquefaction resistance. The ultimate state line is found to be unique and independent of the pre-loading histories in stress space. The Lade instability line prematurely predicts the onset of liquefaction for all samples, both with and without pre-loading histories. The redundancy index is an effective microscopic indicator to monitor liquefaction, and the onset of the liquefaction corresponds to the phase transition state where the value of redundancy index is one, which is true for all cases irrespective of the proportions of sliding contacts.Originality/valueThe liquefaction behaviour of granular materials still remains elusive, especially concerning the effects of pre-loading histories on soils. Furthermore, the investigation of the effects of pre-consolidation histories on undrained behaviour and its comparison to pre-sheared samples is rarely reported in the DEM literature.

Experimental Wave-Based Assessment of Liquefaction Resistance for Different Degrees of Saturation

Abstract This paper presents the results of an experimental program carried out in the laboratory aimed at assessing the liquefaction resistance by correlations between longitudinal wave (P-wave) and shear wave (S-wave) velocities (VP and VS) and cyclic stress ratio from triaxial testing (CSRCTx) for different degrees of saturation (Sr). The liquefaction resistance was assessed using a cyclic triaxial apparatus equipped with Hall-effect transducers and bender elements, combining stress-based (large-strain level) and wave-based (small-strain level) approaches. These tests were carried out in soil specimens at relatively high degrees of saturation, which were estimated during testing by VP measurements interpreted using Biot’s theory. The results revealed that, for the same relative density and confinement stress, the S-wave-based approach did not predict the liquefaction resistance well because of the negligible variation in the stress state and soil stiffness for the assessed Sr values, which were above the air-entry value. In turn, the P-wave-based approach effectively predicted the liquefaction resistance increment of the TP-Lisbon sand for different Sr conditions because of the strong dependency of P-wave propagation on the degree of saturation in granular media. This is a consequence of the most relevant factor conditioning the pore pressure buildup in partially saturated sands, e.g., the compressibility of the occluded air bubbles, which can be detected by VP but not by VS.

Seismic performance of a sheet-pile retaining structure in liquefiable soils: Numerical simulations of LEAP-2022 centrifuge tests

This paper focuses on the numerical simulations of a sheet-pile retaining structure under liquefaction-induced lateral spreading, using data from LEAP-2022 dynamic centrifuge tests conducted at various facilities. The simulations employ an updated pressure-dependent multi-yield surface constitutive model (i.e., OpenSees PDMY03), incorporating dilatancy, cyclic mobility, and associated shear deformation features. To more accurately represent the liquefaction resistance characteristics of medium to dense Ottawa sands during LEAP-2022, the contractive and dilative rules of the PDMY03 model are updated based on experimental observations. Subsequently, the model parameters are calibrated through a series of stress-controlled cyclic direct simple shear (CDSS) tests to closely match the liquefaction strength curves of Ottawa sand. With these calibrated model parameters, dynamic response analyses of the sheet-pile retaining structure in liquefiable soils are performed, and the computed results are directly compared to the centrifuge experimental data. It is demonstrated that the updated PDMY03 constitutive model, combined with the employed computational framework, has the potential to realistically predict the experimental results of the sheet-pile retaining structure subjected to liquefaction-induced lateral spreading. Overall, this comprehensive approach enables a realistic evaluation of the performance of equivalent sheet-pile retaining structures under conditions of seismically-induced liquefaction, as well as other relevant scenarios.

Anisotropy in the Liquefaction Resistance of Fibre Reinforced Sand.

Adding discrete fibres to sand has been seen as a feasible technique to improve sand's strength as well as liquefaction resistance. Considering the anisotropic distribution of fibre orientations, the anisotropy in the liquefaction resistance of the reinforced sand is also introduced using fibres. Here, the triaxial compression and extension test results of unreinforced and fibre-reinforced sand in different density states are provided, from which the anisotropy in the liquefaction resistance of fibre-reinforced sand is demonstrated. Fibre reinforcement improves the liquefaction resistance of sand by introducing both the densifying effect and the confining effect. The inclusion of fibres increases both the slope and the intercept of the strength envelope in comparison with the unreinforced sand under triaxial compression, while the strength envelope is not affected by fibres under triaxial extension. Stress contribution of fibres makes the ESP of the composite under undrained loading reverse its direction to develop even though the phase transformation is absent. The stress ratio initiating the ESP reversal is irrespective of the fibre content but dependent on the density state under triaxial compression. Under triaxial extension, the stress ratio initiating the ESP reversal remains the same in the samples with varied density states and fibre contents. The mechanism correlating to the strength envelope and ESP reversal of the fibre-reinforced sand was demonstrated following a rule of mixture based constitutive modelling framework. By introducing an alternatively defined pore pressure ratio that incorporates the stress contribution of fibres, the liquefaction state of the fibre reinforced sand is reasonably assessed. Liquefaction remains absent in the sand once the fibres are mixed. The anisotropy in the liquefaction resistance of fibre-reinforced sand arises, as the predominant role played by the fibres to suppress the liquefaction is different when varied loading paths are involved, which is sourced from the anisotropic distribution of fibre orientations.

Effects of coupled seepage and seismic histories on liquefaction resistance of shallow sand deposits

Seismic histories induced by minor earthquakes could improve the sand liquefaction resistance, whereas those induced by strong earthquakes could decrease the sand liquefaction resistance. The action of upward pore fluid seepage on shallow sand deposits during the post-liquefaction process was determined to be one of the mechanisms of these natural phenomena. Based on this background, a series of 1g shaking table tests were carried out to analyze the effects of pore fluid seepage on the sand reliquefaction resistance in subsequent earthquakes. Experimental results showed that the decreasing effects of the seepage history on the sand liquefaction resistance were limited by the input seismic intensities and applied hydraulic gradient (i). Weaker or more extensive seismic motions (cyclic stress ratio, CSR<0.32 or >0.67, respectively) and i values less than 0.5 would not noticeably decrease liquefaction resistance. In the case of inputting successive motions with a medium CSR and i=3.0, the liquefaction resistance of the sand deposits with seepage histories decreased in the first two shakes in comparison with the deposit models without seepage histories. A longer seepage duration correlated to a much lower liquefaction resistance. These results demonstrated that the interaction of the soil layers during reconsolidation should be considered in evaluating the liquefaction risk of the ground.

Dynamic properties of sand with different contents of clay

In this study, a series of dynamic triaxial tests and corresponding simulations using discrete element method (DEM) were conducted on sand with different clay particle contents. The development of pore pressure, axial strain, stress path, and stress–strain curve were analyzed. The contact and pore structure characteristics were further examined through electron microscopy. Subsequently, the concept of a contact-to-particle ratio is proposed to describe the connection behavior. The results show that the influence of the clay particle content on the liquefaction resistance is not monotonous. With an increase in clay particle content, the effective stress of sand cannot reach zero. However, the increase in clay particles reduced the permeability coefficient of the sand, which resulted in weak liquefaction resistance of sand. When clay particle content reached 30–35%, the stress–strain curve failed at an early stage. The contact-to-particle ratio was the smallest when the clay particle content was 35%, that effective contact of the particles is only 15% of that in the pure sand sample. When clay content reached 40–50%, the sand sample gradually exhibited the characteristics of clay.

Seismic response of vibroflotation reinforced coral sand foundation through shaking table tests

The liquefaction damage in dredger coral sand foundation mainly occurs when these materials are subjected to earthquake action. In the past practical engineering, the dredged loose foundations were used to be reinforced by vibroflotation, a traditional foundation reinforcement method. This paper investigated the impact of vibroflotation on the enhancement of liquefaction resistance by the shaking table. Sampled after the earthquake, the microfabric evolution is assessed by μCT system. The macroscopic results from shaking table tests showed that the vibroflotation can effectively inhibit the growth rate of the excess pressure ratios. Meanwhile, the peak excess pressure ratios of vibro-treated foundation are significantly smaller. Moreover, the study uncovers vibroflotation also resists the sandy softening and the stiffness reduction caused by strong shock. The development patterns of dynamic shear stress-strain hysteresis loops show the vibro-treated foundation is more resistant to stiffness attenuation. The microfabric assessment includes the evolution of the particles and the pores. The less increasing CNave and less decreasing APD reveals that vibro-treated foundation can prevent the damage of earthquake better due to the vibro-caused densification. Similarly, both CNave and K50 shows the vibro-point position gets better anti-seismic capacity when compared with the model center. Overall, the results of the microfabric evolution show that more acute variation happens on the untreated foundation after the earthquake, indicating the great improvement of anti-seismic capacity due to vibroflotation.

Experimental Investigation on the Post-liquefaction Behavior of Sands in Simple Shear Conditions

Abstract Experimental evidence shows that earthquake induced liquefaction can occur more than once in sandy soils. Moreover, despite an increase in soil density caused by the dissipation of the excess pore pressure induced by earthquakes, the liquefaction resistance of soils that have experienced liquefaction may be lower than that of virgin soils. This paper offers insight into this topic starting from the analysis of the undrained monotonic behavior of post-liquefied sands by means of tests performed with a simple shear cell equipped with flexible boundaries, which maintains a constant diameter to guarantee the “K0-condition.” The control system of cyclic, reconsolidation, and monotonic phases is described in detail. The experimental results show that neither the relative density, effective confining stress, cyclic stress ratio, nor the direction of shear strain play important roles in the monotonic behavior of post-liquefied soils. Moreover, the comparison between the monotonic response of virgin and post-liquefied soils (prepared by moist tamping technique) shows that it is not affected by the stress–strain history experienced by soils. It can be explained through a microstructural interpretation. According to which, the initial soil fabric generated with the moist tamping method and that formed during liquefaction remain almost unchanged because of the rotation of principal stress directions occurring during simple shear tests. A further confirmation is given by the results of tests performed on specimens prepared by air pluviation method.

Effects of seepage flow on liquefaction resistance of uniform sand and gap-graded soil under undrained cyclic torsional shear

Internal erosion is the transportation of soil particles from within or beneath geotechnical structures, caused by seepage flow, that impacts the subsequent mechanical and hydraulic behaviour of the soil. However, it is difficult to predict the liquefaction resistance of eroded soil due to several factors related to the soil fabric. The present study investigates the impact of seepage flow on the undrained cyclic behaviour of two types of soil: uniform sand and gap-graded soil with a fines content of 20%, using a novel erosion hollow cylindrical torsion shear apparatus. From the results for the uniform sand, the soil fabric formed by moist tamping (MT) leads to higher liquefaction resistance than that formed by air-pluviation (AP). However, after applying seepage flow, the liquefaction resistance of the eroded MT specimens becomes even lower than that of the non-eroded AP specimen. Therefore, the liquefaction resistance of soil is expected to decrease due to the rearrangement of the initially stable coarse particles during seepage flow. On the other hand, the liquefaction resistance of the gap-graded soil tends to increase after the removal of fines as the number of stable contacts between the coarse particles is increased. Under these test conditions, the latter effect is found to be greater for the given gradation, leading to a slight increase in the liquefaction resistance of the tested gap-graded soil after internal erosion. Furthermore, the intergranular void ratio and small-strain shear modulus are seen to be well correlated with the liquefaction resistance of the tested soil.

Static and cyclic liquefaction of granular materials considering grain morphology

In this study, a series of undrained monotonic and cyclic triaxial shear tests were performed on glass sands to evaluate the effect of grain morphology on the static and cyclic undrained response of granular materials. The grain morphology of five test materials prepared with two glass sands with significant shape discrepancy was quantified with an image-based method. The test results show that as the overall regularity decreases, the peak and steady state stress ratios increase, and the dilatancy is suppressed. The development of excess pore water pressure and accumulated axial strain as well as the rate of stiffness degradation are lowered as the overall regularity decreases. The results also reveal that excess pore water pressure is correlated well with the cyclic stiffness degradation index. The liquefaction resistance decreases with the increase of the overall regularity.

Evaluation of liquefaction resistance for single- and multi-phase SICP-treated sandy soil using shaking table test

Evaluation of liquefaction resistance for single- and multi-phase SICP-treated sandy soil using shaking table test

Cyclic Behaviors of Anisotropically Consolidated Gravelly Soils under Triaxial Condition: Effects of Sand Gradation Part of the Soil

Abstract Previous studies have extensively examined the effects of silt contents and gradations on the cyclic behavior of sand and silt mixtures. However, comparable data on the mixture of sand and gravel are limited because of the experimental challenges of getting reliable testing results from gravel-size particles. Furthermore, in several case histories in which liquefaction occurred, the liquefied soils had experienced initial static shear stress because of the sloping ground conditions or the presence of structures and buildings on the site. The effects of initial static shear stress on the cyclic behavior of clean sands have been widely studied, and some recommendations have been suggested for practical engineers. This research aimed to evaluate the effects of the sand gradation part on the cyclic behavior of two gravelly soils, both with 60 % gravel and 40 % sand but different gradations (well-graded vs. uniformly graded). A total of 26 cyclic triaxial tests were carried out on moist-tamped reconstituted specimens of the tested gravelly soils. The specimens were anisotropically consolidated to assess the effects of initial static shear stress combined with sand gradation on cyclic behaviors of the tested gravelly soils. Results of the tests indicated that the gravelly soil with uniform sands had a greater resistance against liquefaction than the one with well-graded sands. The lower cyclic resistance of the gravelly soil with well-graded sands can be attributed to its lower permeability associated with wider gradation and finer particles of the sand part, leading to higher excess pore pressure buildup during cyclic loading. Moreover, a similar increase in the level of initial static shear stress resulted in an increase in the liquefaction resistance of the gravelly soils, whereas the soil with uniform sands experienced a higher increase than the soil with well-graded sands.

Influences of particle size distribution and fines content on the excess pore water pressure generation of sand-silt mixtures under cyclic loading

The mechanical behaviors of binary mixtures are different from that of uniform soils. However, experimental studies on the dynamic responses of sand-silt mixtures considering the combined effects of fines content (FC) and host sand gradation are limited in the literature. In this paper, an experimental program was designed concerning five binary mixtures with three grain size ratios (Rd) and three sand uniformity coefficients (Cus) for investigating the effects of fines content and host sand gradation on both the liquefaction resistance and the excess pore water pressure (EPWP) generation of sand-silt mixtures. Results show that the effect of FC on the liquefaction resistance of sand-silt mixtures depends on relative density (Dr), grain size ratio, and sand uniformity coefficient. The liquefaction resistance of sand-silt mixture can be uniquely characterized by the equivalent relative density Dr* regardless of FC, Dr, and host sand gradation. Relationship between the EPWP ratio Ru and the cycle ratio N/NL for the sand-silt mixtures can be well expressed by the Seed model, which is significantly affected by cyclic stress ratio (CSR), FC, and Dr but insensitive to the change of host sand gradation. A trained artificial neural networks (ANN) model is conducted to predict the fitting parameter β of the Seed model with a maximum difference of 25% between the predicted and measured values. Moreover, there is an arctangent relationship between Ru and shear strain amplitude γa of each specimen, and the fitting parameter A for the relationship is sensitive to the particle size distribution and stress amplitude. A unique relationship between a density-corrected parameter A/Dr* and CSR is proposed regardless of FC and host sand gradation.

DEM simulations on the influence of carbonate precipitation on liquefaction mitigation of sand

Microbially induced carbonate precipitation (MICP) is an effective method to mitigate liquefaction of sands under cyclic shear loading. In this paper, discrete element method (DEM)-based simulations of the cyclic direct simple shear (CyDSS) tests are carried out using a three-dimensional shear box geometry to evaluate the liquefaction resistance of untreated, MICP-cemented, and reconstituted sands. A six-parameter contact model previously used for undrained and drained triaxial tests on sand is used in the DEM analysis. Verification and validation of the DEM model is implemented through modeling of experimental CyDSS results on loose Fraser River sand at several values of cyclic stress ratios (CSR). The DEM model parameters for untreated and microbially treated Ottawa 20–30 sand are obtained by matching the simulated deviatoric stress and excess pore pressure from strain-controlled undrained isotopically consolidated triaxial compression tests. The DEM model is shown to be capable of accurately representing the cyclic strength curves for untreated, treated, and treated but reconstituted sand using parameters derived from the triaxial test data. The simulated stress path, shear strain evolution, and the evolution of coordination number are used to further examine the effect of MICP on liquefaction in CyDSS tests. The DEM model can be used to design cementation levels and develop cyclic strength curves for different types of sands to aid engineers in designing liquefaction mitigation strategies using MICP.

Study on the Liquefaction Mechanism of Mixed-Size Tailings Material Based on Grain Contact State Theory

Tailings ponds serve as high-potential energy structures designed to store waste tailings and other industrial materials. However, they can give rise to significant environmental pollution and pose a substantial threat to social and economic development, as well as the safety of people’s lives and property. Seismic disasters can cause liquefaction of tailings, leading to destabilization and dam failure of tailings ponds, and the evolution of dynamic pore pressure of tailings can indirectly reflect the destabilization process of tailings ponds. Fine grain content is one of the main factors affecting the dynamic strength and pore pressure development of tailings. This article studies the microscopic characteristics of tailings material through microscopic observation, triaxial testing, discrete element simulation, and grain contact state theory, aiming to analyze the influence mechanism of fine grain content on the micromechanics of tailings. Based on the grain contact state theory, the tailings with different fine grain contents are classified into three types: coarse grain tailings, intermediate-size grain tailings, and fine grain tailings, and the grain contact is classified into four different states. In contact state 1, the vibration pore pressure exhibits a “fast-stable” development mode with increasing vibrations. In contact state 2 or 3, the vibration pore pressure develops linearly with vibrations. For contact state 4, the development of vibration pore pressure presents a “fast-stable-sharp” development mode. The effect of fine grain content (FC) on the liquefication of the tailings studied in the present work is as follows. When the fine grain content is FC&lt;30%, the liquefaction resistance of the tailings decreases with the increase of FC. When FC&gt;30%, the liquefaction resistance increases with the increase of FC. When FC=30%, the liquefaction resistance is the lowest, indicating that the critical threshold of the fine grain content of the tailings studied in the present work is FCth=30%.

Experimental investigation of liquefaction characteristics of saturated coral sand subjected to complex cyclic stress paths: Effects of loading frequency

How cyclic loading frequency affects the liquefaction characteristics of saturated coral sand was investigated by performing undrained cyclic shear tests subjected to a 90° jump of principal stress, with consideration given to cyclic stress ratios (CSR) of 0.25, 0.30, 0.35, and 0.40, orientations of major principal stress of 0°, 22.5°, 45°, 67.5°, and 90°, and cyclic loading frequencies ( f ) of 0.05, 0.1, 0.5, and 1 Hz. The test results show that increasing f decreases the generation rate of excess pore water pressure and deformation. Under the same cyclic stress path, the amplitude of deviatoric strain and the excess pore water pressure ratio (ru) have a unique relationship. The unit cyclic stress ratio (USR) was introduced to represent the liquefaction resistance of saturated coral sand under different cyclic loading modes, and increased f leads to increased liquefaction resistance. Under isotropic consolidation, the relationship between the cumulative dissipated energy (Wc) and ru is almost independent of f, CSR, and cyclic stress path. A hyperbolic function model of Wc with the development of ru is proposed, and its applicability is verified against data from the literature.

Framework of a performance-based design for liquefaction resistance

Seismic liquefaction hazards remain a very challenging problem in geotechnical earthquake engineering and are one of the most important aspects currently to update the framework of the liquefaction resistance design from a performance-based perspective. In this paper, by investigating the characteristics of the seismic liquefaction hazard, as well as integrating the existing performance-based earthquake engineering (PBDEE) and advanced risk management theory, the connotation and key points of performance-based liquefaction hazard governance are proposed, and the framework of a performance-based design for liquefaction resistance (PBDLR) is constructed according to the technical system construction rules. The results indicate that the liquefaction hazard has its own characteristics in terms of the hitting target, hazard scale, occurrence mechanism, chain effect, treatment technology, and uncertainty of the influencing factors. Its technical system of hazard governance requires special consideration. The presented PBDLR integrates the advantages of both the advanced risk management theory and the existing performance-based earthquake engineering technology system, and the elements and structure consider the sociality of the target, the integrity of the function, the hierarchy of the composition, and the linkage of the elements and the completeness of the technology. The PBDLR takes the liquefaction hazard governance objective as the primary factor and performance analysis as the technical main body of the framework, and it is equipped with several new elements matching the characteristics of the liquefaction hazard and the requirements for the technical development of an anti-liquefaction design. The PBDLR presented in this paper can provide guidance and a reference for future research and technical development in liquefaction hazard governance.

Experimental Study on Liquefaction Characteristics of Coral Gravelly Soils with Different Particle Size Distributions

Many laboratory studies have shown that particle size distribution (PSD) affects the liquefaction susceptibility of granular materials. However, few studies have focused on the impact of PSD on coral particles. In this study, two different soil families were prepared: one with three levels of mean particle size (D50) with identical uniformity coefficient (Cu)and the other with four levels of Cu with the same D50 for coral gravelly soils. In addition, a series of undrained cyclic triaxial tests were conducted on coral gravelly particles with two groups of PSDs at a relative density of 40% and an adequate confining pressure of 100 kPa. The test results indicated that D50 with identical Cu can affect the undrained cyclic behavior of coral gravelly particles. In contrast, Cu with identical D50 does not impact the undrained cyclic behavior of coral gravelly particles. The developing pore water pressure was uniform when the sample was subjected to the same cyclic loading. For samples with changing D50 values of 2.35, 4.70, and 7.05 mm, increasing D50 improved the cyclic liquefaction resistance. For samples with changing Cu, increasing Cu in the range of 1.06–5.00 first increased and then decreased the liquefaction resistance.