The Sand Compaction Pile (SCP) method is a ground improvement technology that increases the density of the ground by constructing sand piles through penetration and repeated withdrawal/re-driving of the casing pipe. This method is the most widely used liquefaction countermeasure method in Japan. This method has been recognized in previous investigations that its improvement effect is mainly derived from an increase in soil density. However other factors such as unique stress history during the SCP work process also have been reported to contribute to the effectiveness. In order to more accurately reproduce the behavior of the ground during the construction of Sand Piles, a stress history simulating the SCP work process was applied to specimens, and the effects of the stresses were observed. The material used in this test is silica sand. These specimens were prepared by air-pluviation method to reach a relative density of 60% (Dr=60%). The specimens were consolidated with a lateral stress ratio of 0.5 (K0=0.5), then the stress history including lateral pressure increase and cyclic shear stress was applied, and finally, liquefaction resistance was confirmed by cyclic loading. After applying stress history, an increase in liquefaction resistance was observed in these specimens. This increase was larger than that of specimens subjected only to lateral stress increase without a shear stress history.

Recently, the observed devastation on structures due to soil reliquefaction highlights the need to assess the ground improvement techniques' performance under repeated shaking conditions. Ground improvement using stone column reinforcement was most popular due to its multimode benefits, such as installation-induced densification, drainage and shear reinforcement. Though the performance of the stone column improvement technique in liquefaction mitigation was well documented, the de-bonding of aggregates and column contamination due to the intrusion of surrounding soil grains during repeated shaking needs to be explored elaborately for assessing the performance of the technique. Similarly, encasing stone columns with geotextile material has recently been getting attention due to its confining and containment characteristics. Considering the above, the present experimental investigation attempted to use ordinary and geotextile encased stone columns for liquefaction and reliquefaction mitigation of saturated ground. The performance of the treatment technique was evaluated under repeated incremental shaking events. A saturated ground having 800 mm thickness with 40% relative density was used for the study. Four ordinary and encased stone columns having 120 mm diameter and 800 mm length, constituting an 8.0% area replacement ratio, were used for ground reinforcement. Both untreated and treated ground were subjected to repeated incremental acceleration loading, viz. 0.1g, 0.2g, 0.3g and 0.4g with a 5 Hz loading frequency. The generated pore water pressure ratio, soil settlement and foundation settlement for both treatment technique was monitored and compared with the untreated ground. The parameters influencing the performance of the ordinary and geotextile-encased stone column technique against liquefaction and reliquefaction hazards were evaluated and presented.

This study focuses on the pipe uplift in liquefied soil during earthquakes, examining the uplift process and proposing consideration for countermeasures through experiment and numerical simulation. The research emphasizes the additional factor of uplift resistance force and the risk of applying the weight of rigid structure as a countermeasure. The additional factor of uplift resistance force is non-liquefied behavior and suction force at the lower part of the pipe. Also, the risk of applying rigid structure is the accelerating liquefaction behavior at the soil-structure contact area. These results are expected to contribute to developing pipe uplift reduction countermeasures.

Innovative soil improvement methods like calcite-induced precipitation methods have been promising techniques in improving the shear strength of sand. EICP is an innovative bio-inspired approach that has emerged in recent years as an environmentally friendly solution for liquefaction countermeasures. EICP is a candid process to promote the calcium carbonate (CaCO₃)/calcite precipitation obtained by mixing urea (CO(NH₂)₂), calcium chloride (CaCl₂), and urease enzyme. Bio-cementation using EICP helps in the deposition of CaCO₃ in the void space where clogging of the porous medium causes a reduction in porosity and hydraulic conductivity. All these factors increase the soil's strength, leading to soil liquefaction mitigation. In this study, poor-graded silica sand is adopted to evaluate liquefaction resistance. EICP solution consists of 3 g/l urease added with 1 M Urea and 0.67 M Calcium Chloride as cementation solution. The cyclic response under an effective confining pressure of 100 kPa in the pure sand and EICP-treated specimen in 7 days of curing time was studied. Field emission – Scanning Electron Microscopy (FE-SEM) and Energy Dispersive Spectroscopy (EDS) revealed the deposition of calcium carbonate on the interparticle contacts and surface of the sand grains, which enhances the cyclic resistance in the soil.

Liquefaction, a common issue in cohessionless, saturated soils under static and dynamic loading. Inducing partial saturation is a recent method to mitigate the liquefaction of sand by generating gas or air in the pores of saturated sand. Since the fluid bulk stiffness of soil is very sensitive to the presence of gas or air, a small volume of bubbles can significantly affect the pore pressure response to loading. However, conventional measures against soil liquefaction are often expensive and unsuitable for existing structures. This study aimed to assess the effectiveness of the air injection method in preventing liquefaction in saturated sand using cyclic triaxial apparatus. Stress-controlled triaxial tests were performed on loose saturated and treated sand considering different cyclic stress ratio and confining pressure. Additionally, this study examined the durability of entrapped air bubbles under field conditions that may lead to dissolution or escape of air bubbles. To evaluate the long-term stability of the bubbles tests were conducted on partially saturated sand under hydraulic gradient flow condition. The results demonstrated a significant improvement in liquefaction resistance for the treated sand, with a reduced degree of saturation ranging from 95% to 80%. Furthermore, in durability study after downward water flow, the degree of saturation of partially saturated sand slightly increased and remained stable, indicating long-term stability

Reinforcement of existing river levees upon deep liquefiable subsoil is costly, and its effectiveness is often limited. For some conditions, it would be cost-effective to demolish an existing embankment and stabilize the liquefiable subsoil by means of cement-treatment. In the present Japanese design guideline, the entire layer of liquefiable subsoil beneath a river embankment is supposed to be reinforced; however, such construction cost depends highly on the depth of reinforcement. To rationalize the design approach, the present study aims to evaluate the performance of partial reinforcement immediately beneath the embankment. A series of shake-table model tests under a centrifugal acceleration of 50g were conducted where the depth of reinforcement by cement-treatment was varied systematically. The experimental results revealed that the settlement of levee crown can be reduced linearly with the depth of reinforcement relative to the depth of the initial liquefiable subsoil. Besides, the acceleration measured at the levee crown was reduced drastically when partial reinforcement was adopted due to the attenuation of ground motion that propagated through an underlying liquefied soil layer. This side effect would contribute to safe road operation immediately after an earthquake event, and enables prompt repairment of river levees to prepare for aftershocks.

An in-house research and development (R&D) exercise involving a Rammed Aggregate Pier (RAP) ground improvement trial, was undertaken to determine if RAPs were a suitable ground improvement option to mitigate liquefaction, for a significant infrastructure project located within New Zealand. The Pleistocene-aged volcanic derived pumiceous sands encountered below the groundwater table, were assessed using conventional methods to be susceptible to liquefaction. Considering the results of other trials, conventional large strain Cone Penetrometer Testing (CPT) in conjunction with small strain shear wave velocity testing methods, using the seismic cone penetrometer (sCPT), were carried out prior to and following RAP installation to assist in evaluating the effectiveness of the ground improvement. Although the results of the trial demonstrated that the Pleistocene-aged alluvial sands densified following RAP installation, shear wave velocity measurements were much lower than those undertaken prior to installation indicating that the high energy vibratory hammer used to install the piers had disturbed the soil microstructure. The results have highlighted an interesting effect of dynamic ground improvement techniques in geologically older soil deposits. Comparing the results of the trial, with other RAP ground improvement trials conducted around the world demonstrated that current in-situ testing methods and subsequent analysis methods used in evaluating liquefaction potential of soils are generally based on a large database of case histories involving very young, silica-rich soils which have no bonding/cementation (Robertson, 2015) and therefore there are limitations associated with assessing geologically aged soils.