The mitigation of seismic soil liquefaction in sand with fine content presents a challenge, demanding efficient strategies. This research explores the efficacy of Microbial-Induced Partial Saturation (MIPS) as a biogeotechnical technique to improve the liquefaction resistance of sandy soils with plastic fines. By leveraging the natural metabolic processes of indigenous microorganisms, this method introduces biogenic gas production within the soil matrix, effectively reducing its degree of saturation. This partial desaturation alters the soil's response to cyclic loading, aiming to mitigate the risk of liquefaction under dynamic loading conditions. Experimental results from a series of undrained strain-controlled cyclic shear tests reveal that even a modest reduction in saturation significantly enhances the soil's stability against seismic-induced liquefaction. The investigation extends to analyzing the effectiveness of the MIPS treatment in sands with low-plasticity clay content, offering insights into the interaction between microbial activity, soil texture, and liquefaction potential. Results show that while plasticity plays a key role in improving the cyclic response of soils, the influence of MIPS treatment remains noteworthy, even in sand with plastic fines. Additionally, a modified predictive formulation is introduced, incorporating a calibrated parameter to account for the influence of fines' plasticity on excess pore pressure generation.

After sand liquefaction, buried underground structures may float, leading to structural damage. Therefore, implementing effective reinforcement measures to control sand liquefaction and soil deformation is crucial. Stone columns are widely used to reinforce liquefiable sites, enhancing their resistance to liquefaction. In this study, we investigated the mitigation effect of stone columns on the uplift of a shield tunnel induced by soil liquefaction using a high-fidelity numerical method. The liquefiable sand was modeled using a plastic model for large postliquefaction shear deformation of sand (CycLiq). A dynamic centrifuge model test on stone column-improved liquefiable ground was simulated using this model. The results demonstrate that the constitutive model and analysis method effectively reproduce the liquefaction behavior of stone column-reinforced ground under seismic loading, accurately reflecting the time histories of excess pore pressure ratio and acceleration. Subsequently, numerical simulations were employed to analyze the liquefaction resistance of saturated sand strata and the response of a shield tunnel before and after reinforcement with stone columns. Additionally, the effects of densification and drainage of the stone columns were separately studied. The results show that, after installing stone columns, the excess pore pressure ratio at each measurement point significantly decreased, eliminating liquefaction and mitigating the uplift of the tunnel. The drainage effect of the stone columns emerged as the primary mechanism for dissipating excess pore pressure and reducing tunnel uplift. Furthermore, the densification effect of stone columns effectively reduces soil settlement, particularly pronounced around the stone columns, i.e., at a distance of three times the diameter of the stone column.

Seismic loading has been widely recognized as a critical factor contributing to soil liquefaction. This paper introduces centrifuge tests conducted to characterize the seismic response of clayey sand foundations under surcharge induced by upper structures such as dams, with a focus on examining the effectiveness of different liquefaction mitigation measures. Three models with a surcharged block above are considered: one with soil untreated, one improved with stone columns, and the other enhanced by closed diaphragm walls. In addition, a free ground model is tested to examine the dynamic characteristics of the tested soil. Results show that the soil used is prone to liquefaction, but this trend can be somewhat suppressed by the presence of the surcharge. However, the excess pore pressure within the shallow layer keeps rising after shaking, posing the surcharged structure to instability. With the inclusion of stone columns, seepage can be effectively facilitated, thus eliminate the large pore pressure concentration. The construction of closed diaphragm walls effectively reduces the surface settlement by providing lateral restraint of the soil core. This investigation sheds light on the liquefaction mitigation mechanisms of different measures for clayey sand subjected to large overburden and provides references for improving the seismic design.

Liquefaction, a significant hazard triggered by earthquakes, is characterized by a sudden loss of shear strength due to a rise in pore pressure and the corresponding reduction in effective stresses, leading to structural damage and substantial economic losses. Numerous studies have investigated various mitigation measures for liquefaction. Recently, the focus has shifted toward developing environmentally friendly, cost-effective technologies to enhance liquefaction resistance. One such promising technique is induced partial saturation (IPS), which has the potential to serve as a cost-effective, environmentally friendly, and practical solution for both new and existing structures. The IPS mechanism was examined and discussed extensively in the first part of this review. The effectiveness and usability of this approach in the soil are reviewed in the next section, using small, large-scale laboratory and field-scale testing. Following that, microbubble and pore-scale studies are used to quantify durability and stability. The review has provided several key recommendations to address the current challenges and limitations of the technique, aiming to enhance its effectiveness and stability. Given the ongoing research and the need to ascertain their suitability for practical applications, the existence of a comprehensive literature review becomes essential. This review will provide researchers with valuable insights into the current state of knowledge in this field and serve as a foundation for future studies.

One effective technique for mitigating the earthquake-induced liquefaction potential is the installation of stone columns. The permeability coefficients of stone columns are high enough to cause a high seepage velocity or expedited drainage. Under such conditions, the fluid flow law in porous media is not linear. Nevertheless, this nonlinear behavior in stone columns has not been evaluated in dynamic numerical analyses. This study proposes a dynamic finite element method that integrates nonlinear fluid flow law to evaluate the response of liquefiable ground improved by stone columns during seismic events. The impact of non-Darcy flow on the excess pore pressure and stress path compared to conventional Darcy law has been investigated numerically in stone columns. Furthermore, the effects of different permeability coefficients and stone column depths have been studied under near and far field strong ground motions. The results indicate that the non-Darcy flow increases the excess pore water pressure as high as 100% in comparison to the Darcy flow.

Electrolysis desaturation is an emerging ground improvement technique with significant potential for widespread application in liquefaction mitigation. This method reduces the saturation of foundation soils, thereby decreasing soil liquefaction potential during earthquake. To date, there is still a lack of systematic research on the microstructure evolution of silica sands during the electrolysis desaturation treatment. In this study, non-destructive low-field nuclear magnetic resonance (NMR) technology was employed to investigate the effects of electrolysis desaturation on the silica sands at the microscale. The results showed that the electrolysis desaturation treatment had negligible effects on the structures of micropores and mesopores. The macropores in fine sand expanded during electrolysis, and the increasing current amplified the extent of this expansion. Conversely, in coarse sand, the macropores contracted during electrolysis. Bubbles generated by high-current electrolysis tend to aggregate, causing cracks and surface uplift in the fine silica sand. For the coarse silica sand, the generated gas accumulates within the existing voids, resulting in an insignificant impact on the soil structure. The electrolysis desaturation treatment primarily facilitated the expulsion of free water in both fine and coarse silica sands. In fine silica sand, employing a high current can reduce saturation more effectively within the same duration, but it also allows for more gas bubbles to escape after resting. Coarse silica sand maintained a high desaturation efficiency due to its greater porosity. This study provides a rational explanation in microscale of the structural impacts of electrolysis desaturation treatment on foundation soils.

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.