Loose sandy soil layers are prone to liquefaction under strong earthquakes, causing damage to civil engineering structures inside or upon the liquefied ground. According to the present Japanese design guideline on liquefaction countermeasures for river levees, the entire depth of the liquefiable subsoil below river embankments should be improved. However, this approach is not economical against deep liquefiable subsoil. To rationalize the design approach, this contribution investigated the performance of a floating-type cement treatment method, in which only the shallower part of the liquefiable subsoil is reinforced. A series of centrifuge shaking table model tests was conducted under a 50g environment. The depth of improvement (cement treatment) was varied systematically, and the effect of the sloping ground was examined. The experimental results revealed that the settlements of river embankments can be reduced linearly by increasing the depth of improvement. Moreover, the acceleration of embankments can be reduced drastically by the vibration-isolation effect between the cement-treated soil and the liquefiable soil. These effects contribute to the safe retention of the embankment shape even when the liquefied sloping ground causes lateral flows. Towards practical implementation, discussions on the effect of permeability on cement-treated soil were expanded. Furthermore, the stress acting on cement-treated soil during shaking was measured using an acrylic block to explain the occurrence of cracks in the soil. (c) 2025 Japanese Geotechnical Society. Published 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/).

Earthquake-induced soil liquefaction causes ground and foundation failures, and it challenges the scientific community to explore the liquefaction problem in deep deposit under strong shaking. Due to the capacity limitation of physical modelling facility, it is difficult to reproduce soil liquefaction response of deep sand ground by centrifuge shaking table test. To address this problem, a suite of centrifuge model tests were conducted with the aid of Iai's Type III generalized scaling law (i.e., GSL) to observe the liquefaction response of deep sand ground, where Models 1 and 2 were used to validate the GSL and Model 3 with the validated GSL stands for the deep sand ground with prototype depth of 80 m. The test results of Models 1 and 2 indicate that GSL generally performs well for small-strain shear modulus, nonlinear dynamic response of acceleration and the generation of excess pore water pressure, but leaves considerable errors for post-shaking dissipation process and ground settlement with large plastic strain. The test results of Model 3 indicate that liquefaction is also possible in depth of 30-40 m under shaking event of PBA = 0.4 g and Mw = 7.5. For deeper depth without triggering of liquefaction, a depthdependent power function relationship between the peak excess pore water pressure and Arias intensity has been established. The test results also revealed that consolidation and earthquake shaking history contribute to the development of soil anisotropy in a deep ground, leading to a continuous increase of anisotropy degree, which could be evaluated using the small-strain shear moduli in different stress planes under orthogonal stress conditions.

Stone columns are a resultful measure to increase the bearing capacity of soft or liquefiable foundations. The centrifuge model test and finite element method were employed to investigate the bearing capacity and deformation behavior of the stone column-reinforced foundation. Study shows that the modulus of the reinforced foundation exhibits significant anisotropy. A bulging deformation area is identified in the reinforced foundation where obvious horizontal deformation of the stone column occurs. The ratio of the column stress and soil stress is observed to change violently in this area. A homogenization technique is consequently deduced by employing the column-soil stress ratio as a key variable. The definition of the column-soil stress ratio is extended to reasonably describe the column-soil interaction under different stress levels and its approximation method is given. Based on the Duncan- Chang E-nu model, a simplified method using the homogenization technique is proposed for the stone column reinforced foundation. The proposed homogenization technique and simplified method have been validated by the centrifuge model tests and finite element analyses. This method properly addresses the nonlinear spatial characteristic of deformation and the anisotropy of the stone column reinforced foundation.

A critical investigation of three constitutive models for clay by means of analyses of a sophisticated laboratory testing program and of centrifuge tests on monopiles in clay subjected to (cyclic) lateral loading is presented. Constitutive models of varying complexity, namely the basic Modified Cam Clay model, the hypoplastic model with Intergranular Strain (known as Clay hypoplasticity model) and the more recently proposed anisotropic visco-ISA model, are considered. From the simulations of the centrifuge tests with monotonic loading it is concluded that all three constitutive models give satisfactory results if a proper calibration of constitutive model parameters and proper initialisation of state variables is ensured. In the case of cyclic loading, the AVISA model is found to perform superior to the hypoplastic model with Intergranular Strain.

This study presents a series of centrifuge model tests that were conducted to investigate the grouting mechanism and its effect during rectangular pipe jacking in soft soil. A new jacking grouting device was developed to simulate the entire grouting process in the centrifuge model tests. The influence of grouting on the friction at the lining-soil interface and vertical displacement of the tunnel lining was analysed. In addition, the impact of the grouting slurry's viscosity and fluid loss on ground surface settlement and the friction at the pipe-soil interface was also examined. The results indicate that grouting plays a significant role in mitigating the friction and vertical displacement of the tunnel lining caused by excavation. Furthermore, the study shows that reducing the viscosity of the grouting slurry can reduce the friction coefficient at the pipe-soil interface, thus facilitating the advancement of pipe jacking. The use of a low fluid loss grouting slurry is also recommended to improve control over ground surface settlement. These findings are crucial for enhancing the efficiency and safety of rectangular pipe jacking in soft soil.

The deformation characteristics of river embankments on soft ground, improved by circular deep mixed columns and a combination of circular and grid-form columns, were investigated via two centrifugal model tests. The results indicate that the slope stability of the river embankment was effectively sustained in both cases. The combined reinforcement method exhibited superior overall performance, significantly reducing settlement. The greatest settlement was observed at the top of the river embankment, and although the settlement had not fully stabilized one year after construction, the settlement rate had slowed. Compared with the circular reinforcement alone, the river embankment maximum settlement was reduced by 25.3% in the combined reinforcement. Additionally, the grid-form columns effectively reduced the horizontal displacements in the middle and lower parts of the foundation. The deep-mixed columns performed effectively in providing support and reinforcement, and none of the piles reached the bending capacity during the test process. Given the stiffness difference between the columns and the surrounding soil, the stress distribution exhibited a stress concentration effect in the model. The measured column soil stress ratio ranged between 2 and 3, which is considered reasonable. The pronounced stress concentration effect of the mixing columns contributed to a faster consolidation rate of the foundation. On the basis of the measured settlement and excess pore water pressure, the degree of consolidation of the circular column-reinforced foundation one year after construction reached over 90% and 80%, respectively. For the foundations reinforced with combined circular and grid-form deep mixed columns, the degree of consolidation reached over 80% and 75%, respectively.

BackgroundThe slope failures triggered by heavy rainfall are challenging to predict. However, their severe impact and potential for extensive damage emphasize the urgent need for effective strategies to mitigate these risks. This study aimed to investigate the effects of pore water pressures (PWPs) and pore air pressures (PAPs) on slope failure during heavy rainfall under centrifuge condition. Three centrifuge rainfall model tests were conducted with varying rainfall intensities (I) and relative densities (Dr). In this experiment, the slope model was subjected to a centrifugal acceleration of 30 G.ResultsIn all cases, slope failures started at the slope toes when the PWPs became positive and phreatic surfaces appeared on the slope surface. In the Toyoura sand case, the PAPs increased slightly at the slope crest, hardly changed at the slope toe, and oscillated at the slope shoulder due to rainwater infiltration. The entire slope failure was observed in this case. In the Silica sand cases, only localized slope toe failures were observed. The PAPs slightly oscillated with small changes in the silica sand case with a relative density of Dr = 50%. However, in the case with a Dr = 25%, the PAPs at the slope toe significantly increased compared to the other parts, and the oscillations were comparatively large. After the first failure occurred at the slope toe in the silica sand case with a Dr = 25%, cracks and slip lines appeared at the slope crest.ConclusionsThe three cases illustrated the complex relationship between soil properties, rainfall intensity, and the dynamics of pore water and pore air pressure on slope stability during heavy rainfall. From the behaviour of PAPs and PWPs in all cases, it was found that the transition from air to water occurred smoothly, and the isolation of air was not observed even during heavy rainfall. Changes in PAPs were far smaller than those in PWPs, indicating a smaller impact on slope stability than PWPs.

Offshore wind power is a new type of clean energy with broad development prospects. Accurate analysis of the uplift capacity of offshore wind turbine foundations is a crucial prerequisite for ensuring the safe operation of wind turbines under complex hydrodynamic conditions. However, current research on the uplift capacity of suction caissons often neglects the high-sensitivity characteristics of marine soils. Therefore, this paper first employs the freeze-thaw cycling procedure to prepare high-sensitivity saturated clay. Subsequently, a single-tube foundation for wind turbines is constructed within a centrifuge through a penetration approach. Ten sets of centrifuge model tests with vertical cyclic pullout are conducted. Through comparative analysis, this study explores the pullout capacity and its variation patterns of suction caisson foundations in clay with different sensitivities under cyclic loading. This research indicates the following: (1) The preparation of high-sensitivity soil through the freeze-thaw procedure is reliable; (2) the uplift capacity of suction caissons in high-sensitivity soil rapidly decreases with increasing numbers of cyclic loads and then tends to stabilize. The cumulative displacement rate of suction caissons in high-sensitivity soil is fast, and the total number of pressure-pullout cycles required to reach non-cumulative displacement is significantly smaller than that in low-sensitivity soil; (3) the vertical cyclic loading times and stiffness evolution patterns of single-tube foundations, considering the influence of sensitivity, have been analyzed. It was found that the secant stiffness exhibits a logarithmic function relationship with both the number of cycles and sensitivity. The findings of this study provide assistance and support for the design of suction caissons in high-sensitivity soils.

Due to the frequent occurrence of urban deep covered karst collapse disasters under the strong interference of human engineering activities, the further expansion of the city's deep underground space has been seriously constrained. To study the deep covered karst failure mode and collapse mechanism under static overloading of dense building groups, a centrifugal model test was carried out for the first time based on the actual case of karst in north China. The results indicated that the damage mode of urban deep covered karst collapse under dense building groups is overall collapse, and the critical damage condition for inducing deep covered karst collapse damage is the building floor area ratio of 3.9. Based on the centrifugal model test, it is revealed that the collapse of the upper covering clay layer first started with larger-diameter cavities and then gradually transitioned to smaller-diameter cavities. The crack evolution pattern was mainly from the major penetrating cracks that gradually developed into small cracks, which finally led to the collapse surface shape being concave. Comparing the clay thickness after consolidation, it can be found that the upper covering soil layer is reduced by 16.5 cm on average, accounting for 69% of the height of the covering layer. This study provides technical guidance for the prevention and control of deep covered karst collapse disasters in urban areas.

The h-type anti-slide pile (h-pile) plays a crucial role in mitigating soil-rock mixture slope (SRMS) instability. Despite its significance, the limited availability of research outcomes has constrained the practical application of h-piles for SRMS reinforcement. This study employs three centrifuge model tests to investigate the behavior and performance of h-pile-reinforced SRMS under rainfall conditions. We systematically describe the response of earth pressure on the pile side and behind the pile, bending moment along the pile, and pore water pressure at the slope toe and pile side. This elucidates the evolution of soil arching for h-piles under rainfall conditions. The results reveal that rainfall duration influences the distribution pattern of earth pressure on the pile side, while the distribution pattern of bending moment for the h-pile remains unaffected. Additionally, the soil arching pattern between piles demonstrates joint arching, involving the combined action of frictional arching and end-bearing arching. The evolution process of soil arching between piles under rainfall conditions gradually dissipates from bottom to top and from far to near.