Liquefaction resistance and post-liquefaction shear deformation are key aspects of the liquefaction behavior for granular soil. In this study, 3D discrete element method (DEM) is used to conduct undrained cyclic triaxial numerical tests on specimens with diverse initial fabrics and loading history to associate liquefaction resistance and post-liquefaction shear deformation with the fabric of granular material. The influence of several fabric features on liquefaction resistance is first analyzed, including the void ratio, particle orientation fabric anisotropy, contact normal fabric anisotropy, coordination number, and redundancy index. The results indicate that although the void ratio and anisotropy strongly influence liquefaction resistance, the initial coordination number or redundancy index can uniquely determine liquefaction resistance. Regarding post-liquefaction shear deformation, the above quantities do not dictate the shear strain induced after initial liquefaction. Instead, the mean neighboring particle distance (MNPD), a fabric measure previously introduced in 2D and extended to 3D in this study, is the governing factor for post-liquefaction shear. Most importantly, a unique relationship between the initial MNPD and ultimate saturated post-liquefaction shear strain is identified, providing a measurable state parameter for predicting the post-liquefaction shear of sand.

The bank protection measures of waterways shall become more environmentally friendly in the future including the use of plants instead of stones. The low levels of protection provided by plants in the early phase after planting requires a process-based understanding of soil-wave-interaction. One process that is considered essential is liquefaction where the soil undergoes a phase-change from solid-like to fluid-like behaviour which could reduce the safety of the system. The aim of this publication is to analyse the results of column experiments on wave-induced soil liquefaction and to develop a numerical model which is able to describe the entire process from the pre-liquefaction phase to the following reconsolidation in order to support the analysis of liquefaction experiments. Numerical simulations of the column experiments were done using a fully coupled hydro-mechanical model implemented in the open-source software FEniCS. A permeability model derived from granular rheology allows the simulation of dilute as well as dense suspensions and sedimented soil skeletons. The results of the simulations show a good agreement with the experimental data. Theoretical limits in the liquefied state are captured without the common modelling segmentation into pre-and post-liquefaction phase. Due to the modular structure of the implementation, the constitutive setting can be adjusted to incorporate more complex formulations in order to study the influence of wall friction and non-linearity in soil behaviour.

Geocells have become an integral part of many geosystems like road and railway embankments, retaining walls and foundations, attributed to their multiple merits in terms of stability and strength, but their contributions towards liquefaction mitigation are unknown. The present study aims to understand the role of geocell reinforcement on the liquefaction and post-liquefaction shear response of saturated sands through monotonic and cyclic triaxial tests. Low-strength geocells of required physical and mechanical properties were fabricated through ultrasonic welding of 3D printed polypropylene (PP) sheets. The liquefaction benefits of including a single geocell in sand were quantified in terms of the reduction in pore water pressure, retardation in stiffness degradation and delay in the retardation of effective stress. In general, the inclusion of geocells delayed liquefaction, with higher beneficial effects at lower initial confining pressure, higher cyclic strain amplitude and higher cyclic loading frequency. The maximum benefit measured in terms of percentage rise in the number of cycles needed to liquefy was calculated to be about 230 %. Geocell reinforcement also helped in the quick regain of post-liquefaction shear strength and stiffness.

A series of undrained triaxial tests was conducted to investigate the effect of crushed mudstone with the immersion-induced degradation on the liquefaction and post-liquefaction properties, and the undrained shearing behavior without precedent cyclic-loading histories of sands containing crushed mudstone. The tested materials with a main particle diameter of 2-0.85 mm were prepared by mixing sands and crushed mudstone to reach the prescribed mudstone content defined by dry mass ranging from 0% to 50%. The mixtures were subjected to immersion under a certain stress level and were subsequently tested. In addition, one-dimensional compression tests were also supplementally performed to visually observe the immersion-induced degradation of crushed mudstone. The test results mainly showed that: (1) the liquefaction resistance, the post-liquefaction undrained strength, and the undrained strength without a precedent cyclic-loading history decreased significantly with increasing mudstone content, M-c, up to 20%; (2) even a small amount of crushed mudstone affected these strengths; (3) the above-mentioned large reductions in the strengths were attributed to the immersion-induced degradation of crushed mudstone; (4) at M-c > 20%, the liquefaction resistance increased while the significant increase in the undrained static strengths with and without precedent cyclic-loading histories was not observed; and (5) the increase in the liquefaction resistance at M-c > 20% may have been attributed to both the gradual increase in the plasticity and the formation of the soil aggregates among deteriorated crushed mudstone, while the increase in the specimen density did not play an important role in such behavior. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

To provide new insights into the liquefaction and post-liquefaction behaviors of calcareous sand with and without geosynthetics reinforcement, a series of multi-stage cyclic triaxial tests were conducted. The geosynthetics employed in this study include geogrid, geotextile, and geotextile-geogrid composite. The multi-stage tests consist of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading without excess pore pressure dissipation. The effect of different arrangements of reinforcement layer on the behaviors of calcareous sand is examined and discussed in this study. The test results indicate that a unique relationship can be observed between the double amplitude axial strain and the pore pressure ratio of calcareous sand, irrespective of the influence of reinforcement layer arrangement, providing an effective means of predicting the strain at a given pore pressure level. The liquefaction resistance of calcareous sand increases with the increase in the number of reinforcement layer and decreases with the increase in the distance from the first layer of reinforcement to the sample's top surface. Compared to geogrid and geotextile, the proposed geotextilegeogrid composite exhibits better efficiency in enhancing the liquefaction resistance of calcareous sand. The reinforcement also accelerates the recovery of strength for liquefied calcareous sand and increases the maximum shear strength of sand at large axial strain during the post-liquefaction stage.

Liquefaction-induced large deformations in sloping ground caused heavy damage to buildings and infrastructures during earthquakes, and its evaluation and mitigation challenge. In this study, a series of soil element tests using hollow cylinder apparatus (HCA) were conducted to investigate the relationship between residual volumetric strain and residual shear strain of medium dense to dense saturated sand with moderate initial static shear stress. The soil element tests indicate that the developments of residual volumetric strain and residual shear strain are dominated by the Post-liquefaction Deformation Potential (PLDP) of soil, which is well correlated to the maximum cyclic shear strain developed during cyclic loading. Then, the applicability of PLDP to characterize the post-liquefaction deformation response in gently sloping ground was investigated by centrifuge model tests without and with stone column improvement. The model tests of medium dense and dense sand slopes proved the applicability of PLDP preliminarily. The mitigation mechanisms against settlement and lateral spreading in gentle slopes by densification and drainage effects induced by stone columns were also observed and discussed. The present study provides the conceptual term of PLDP for evaluating post-liquefaction deformations of natural and stone column-improved gently sloping grounds, which helps to develop mitigation techniques for liquefiable sloping ground subjected to earthquake loadings.