Over the past years, ground densification and soil drains have been commonly used as countermeasures against the consequences of seismic soil liquefaction. However, the state-of-practice for designing such mitigation methods is typically for free-field conditions, without considering seismic soil-structure interaction (SSI) or structure-soil-structure interaction (SSSI). In this paper, three-dimensional (3D), fully-coupled, nonlinear finite element analyses, validated with centrifuge experimental results, are used to evaluate how the mitigation mechanism (e.g., densification, enhanced drainage, or their combination) affects the seismic performance of adjacent, similar and dissimilar, inelastic, shallow-founded structures on liquefiable sites. A combination of densification with enhanced drainage under and around the entire footing is shown as the most effective strategy to notably reduce the mitigated foundation’s permanent settlement and tilt (although not always to acceptable levels), regardless of building spacing. Enhanced drainage alone may reduce foundation’s average settlement, but it does not necessarily reduce tilt when near another structure. For the conditions evaluated, the presence of either mitigation method under one structure is shown to notably amplify the permanent tilt and possibly the flexural deflections of its unmitigated neighbor at shorter spacings (S < W/3 where S is the edge-to-edge building spacing and W is the building width), while having a minor impact on its settlement. The results indicate that mitigation (either densification, enhanced drainage, or their combinations) must be designed with extreme care in urban environments, with the goal of improving the overall performance at a systems level for the building as well as its surrounding structures.

Induced Partial Saturation (IPS) is considered one of the most innovative and promising countermeasures against liquefaction, due to its low-cost, eco sustainability and its applicability in the urbanized areas, where the need to reduce the risk of liquefaction must be addressed taking into account the integrity of the existing buildings. IPS consists of injecting gas/air into pore water in order to increase the volumetric compressibility of the fluid phase and thus, increasing soil liquefaction resistance. Although the effectiveness of IPS has been confirmed at small and large scale, its use in practical applications is not yet widespread. This can be basically attributed to a lack of design tools. In this paper an energetic approach has been used to build useful design charts, based on the results of in situ (CPT or SPT) tests. The charts allow to choose the degree of saturation to apply in situ to have a desired increase of resistance. A simple application to the case study of Marina District (California) has lastly been shown.

In geotechnical engineering practice, several seismic liquefaction countermeasures have been suggested to mitigate the damage scale induced by earthquakes. Cement-induced ground improvement is the common preventative measure, where ground solidification mainly involves grout material injection into the ground (e.g., depth of 10 to 20 m). However, cement injection has environmental concerns (e.g. ground water pollution) and is ineffective in terms of seismic wave attenuation. Recently, biopolymer-based soil treatment (BPST) has been actively implemented in geotechnical engineering practices as an environmentally friendly approach. In this study, an enhanced BPST material (Cr³⁺-induced cross-linked xanthan gum) has been introduced to improve the seismic resistance of liquefiable loose sand. A cyclic direct simple shear apparatus was used to assess the cyclic stress ratio (CSR) and cyclic resistance ration (CRR) of clean and Cr³⁺-xanthan gum – BPST sand samples. According to experimental findings, the BPST condition with Cr³⁺-xanthan gum has higher CRR values than the clean and sole xanthan gum-treated sand cases. The experimental findings and seismic ground response analysis support the effectiveness of Cr³⁺-xanthan gum-BPST as a countermeasure to reduce the seismic risk of loose liquefiable sandy grounds.

The presented paper aim is to validate the application of the log piling method as a safe, cost-effective and environmentally friendly densification method for reducing the risk in terms of soil liquefaction during seismic excitation. Recent applications of the technique in Japan assume that log piles shall penetrate the whole or most of the liquefiable soil layer in order to prevent damage during earthquakes. However, such mindset might lead to economically ineffective solutions as in some cases improvement depth might become unreasonably great. Previous studies and observations prove that shallow ground improvement significantly influences the seismic response of the “liquefiable soil – improved zone – superstructure” system in a favorable way – quantitively represented by the reduction of liquefaction-induced total settlement and penetration settlement. The purpose of the paper is to demonstrate the outcome of small and medium-scale 1-g shaking table tests for the sake of providing practical guidelines for setting optimum dimensions of the modified ground zone. In order to do so, first series of tests (small-scale) focus on an extended parametric study which delivers conclusions regarding improvement width, center-to-center piles distance and improvement depth to liquefiable layer thickness ratio, whereas the second one (medium-scale) aims to give a suggestion for the minimum absolute value of the piles’ length. This paper allows engineers in practice to follow a full step-by-step procedure for adopting the log-piling method as liquefaction mitigation countermeasure for small residential buildings.

Dynamic centrifuge tests were used to simulate seismic performance of a five-story building with footings supported by micro-piles during and after liquefaction process. The comparison test was a shallow-footed five-story building model without piles. The test results demonstrated that small size pile has an obvious effect of restraining the postearthquake settlement and inclination of the building. The deeper the small size pile penetrates into the non-liquefied bearing soil layer, the better the improvement effect. During the shaking, it was observed that the axial instrumented

piles displayed symmetrical reverse axial force waveforms, and the lateral instrumented piles showed similar and in phase bending moment wave forms. After the earthquake, as the excess pore water pressure dissipated, the negative frictional force of the axially instrumented piles increased significantly. Whether it is axial force or bending moment, as the shallow soil liquefies, it increases in the deeper part of the foundation pile, indicating that the shallow soil loses its bearing capacity due to liquefaction and the seismic load is transferred to the deep soil.

The SCP (Sand Compaction Pile) method is the most widely adopted liquefaction countermeasure in Japan, and the first academic report of the improvement effect of the SCP method was published in an article on earthquake investigation after the 1978 Miyagi-ken-oki Earthquake. Despite subsequent seismic events, such as the 1995 Hyogoken Nambu Earthquake and the 2011 Off the Pacific Coast of Tohoku Earthquake, both inland and plate boundary occurrences, minimal damage has been reported in regions where SCP ground improvements were implemented. This paper reports on the SCP method’s effectiveness during major past earthquakes and the results of analyses based on subsequent investigations. Furthermore, as recent findings, the results of shaking table tests simulating the installation procedure with penetration and construction (pulling out and re-driving) process to the SCP method. The test results reveal that these construction processes with cyclic shear affect the improvement effects of "increase in lateral stress" and "stabilization of microstructure" in addition to "increase in density”.