Precast driven piles are extensively used for infrastructure on soft soils, but the buildup of excess pore water pressure associated with pile driving is a challenging issue. The process of soil consolidation could take several months. Measures are sought to shorten the drainage path in the ground, and permeable pipe pile is a concept that involves drainage channels at the peak pore pressure locations around the pile circumference. Centrifuge tests were conducted to understand the responses of permeable pipe pile treated ground, experiencing the whole pile driving, soil consolidating, and axially loading process. Results show that the dissipation rate of pore pressures can be improved, especially at a greater depth or at a shorter distance from the pile, since the local hydraulic gradient was higher. Less significant buildup of pore pressures can be anticipated with the use of permeable pipe pile. For this, the bearing capacity of composite foundation with permeable pipe pile can be increased by over 36.9%, compared to the case with normal pipe pile at a specific time period. All these demonstrate the ability of permeable pipe pile in accelerating the consolidation process, mobilizing the bearing capacity of treated ground at an early stage, and minimizing the set-up effect. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. 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/).

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.

Infrastructure projects on slopes that are exposed to changes in water levels face unique challenges. Fluctuations in water levels can significantly impact the stability and integrity of the slope. Stresses affecting soil nails are influenced by various factors, including changes in groundwater levels due to rainfall, temperature variations, or human activities. While studies have addressed the use of soil nails to enhance slope stability, there has been limited attention to the performance and serviceability of soil nails under cyclic changes in the groundwater table. Lateritic slopes are susceptible to instability due to factors such as extensive weathering, inadequate drainage, and steep cuts. Erosion and slope failure are exacerbated by insufficient vegetation cover, climate-induced degradation, and human activities. This highlights the importance of understanding the stress generated and the interaction between the soil and reinforcing material. In this study, centrifuge modelling was employed to simulate cyclic saturation and desaturation of a lateritic slope in response to fluctuations in groundwater levels. Four centrifuge tests were conducted on slopes with a 5V:1H ratio, both unreinforced and reinforced, at two different soil densities. The slopes were subjected to cycles of saturation and desaturation using a seepage simulator located behind them. Both unreinforced and reinforced slopes exhibited stability within a gravitational range from 1 to 40 g, showing no apparent cracks or settlements. Following the initiation of water flow through the slope, a gradual flow slide failure occurred in the unreinforced slope. When exposed to fluctuating water levels, the utilization of soil nails prevented the development of a continuous slip plane in higher-density slopes, while lower-density modelling revealed a failure slump and tensile cracks on the slope surface. Increased excess pore water pressure during ground saturation reduced effective stress on soil nails, reducing their tensile resistance. Conversely, lowering groundwater levels increased effective stress, mobilizing axial forces in the nails. This cyclic variation caused visible changes in settlements, strains, and tensile cracks in the slope following saturation and desaturation cycles.

Research has been carried out to study the effects of new tunnelling on an existing adjacent tunnel to ensure the safety and serviceability of tunnels. Prior studies on twin-tunnel interaction have mostly centred on simplifying perpendicularly crossing tunnelling in a single-layered soil stratum. New tunnel excavation beneath an existing tunnel at different skew angles in two-layered strata can lead to different patterns of stress redistribution and adverse impacts on the existing tunnel. In this paper, results of three-dimensional centrifuge and numerical modelling carried out to study the twin-tunnel interaction with varying advancing orientations and layered soils will be reported. The influence of new tunnel excavation on an existing tunnel was simulated in-flight by controlling both the tunnel weight and volume losses. An advanced hypoplastic constitutive model that can capture stress-, path, and strain-dependency of soil behaviour is utilised for numerical back-analyses and parametric studies. Cases investigated include twin-tunnel interaction at three different skew angles (30 degrees, 60 degrees, 90 degrees) in a uniform sand layer and at skew angle of 90 degrees in two-layered sand with different relative densities and thicknesses. Distinct load redistribution patterns will be presented to explain deformation mechanisms of the existing tunnel at different tunnel advancing skew angles to highlight the effects of tunnelling orientation. The results of perpendicularly crossing tunnelling in twolayered sand will also be reported and compared to reveal the influence of layered soil. The findings and new insights can help engineers better estimate advancing tunnelling effects on existing tunnels and enhance the safety of tunnel construction.

Soil bioengineering using vegetation has been considered an environmentally friendly solution to improve slope stability. Although several studies have demonstrated the contribution of vegetation to slope stability, a gap in understanding the mechanisms of grass root-soil interactions under rainfall conditions remains. This study investigates the effects of the roots of vetiver grass ( Chrysopogon zizanioides) ) on the hydromechanical behaviour of an unsaturated soil slope using the centrifuge modelling technique. The changes in pore water pressure and slope deformation were monitored during the test. The monitored data were subsequently back-analysed and interpreted using seepage-stability analyses. In addition, this study focused on evaluating the effect of roots on slope stability, considering safety and pore water pressure during rainfall. Results revealed that the vetiver roots remarkably affected the initial suction of the slope by increasing the soil's air-entry value. The increased suction and the additional cohesion provided by the roots enhanced slope stability under rainfall conditions.

The issue of bridge end bumps is a critical concern in the failure of bridge and bridge approaches. A series of novel centrifuge tests utilizing a ring model box were conducted to investigate settlement and its induced damages at the bridge approach. A new mitigation method, the deep-seated slab, for bridge end bumps was modeled in the test. This study analyzed the decisive role of pavement stiffness, soil modulus, and load cycles on deformation from the perspective of structure-soil interaction under standard traffic load conditions. The test results show that when deep-seated slabs are used, the deformation of the bridge approach follows an exponential decay pattern, eventually stabilizing after approximately one slab length. Furthermore, the upper and lower bridges exhibit distinct damage modes, i.e., the bridge damage by wheel collision at the upper bridge and the pavement damage by wheel impact at the lower bridge. The damage zone on the pavement is approximately 1.7 times the wheel width and the damage zone on the bridge 2.6 times. Finally, a predictive model for the deformation of bridge approaches was proposed, considering the effect of pavement stiffness, subgrade soil modulus, and load cycles. The relationship between the deformation and the three normalized variables conforms to the quadratic polynomial function.

Rainfall-triggered slope failures have increased globally by over 70% in the last decade, as a direct implication of climate change. This can be counteracted by having good quality granular material to allow quick dissipation of pore water pressures. In the absence of permeable soils, the response of slopes with marginal soil during infiltration events can be improved by the simultaneous provision of preferential drainage channels and reinforcement function. The study discusses the effectiveness of inclusion of an assembled geosynthetic material possessing drainage action of a non-woven geotextile and reinforcement characteristic of woven geogrid, referred as a hybrid-geosynthetic. Centrifuge modelling technique was adopted, appropriate scaling laws were established, and a series of centrifuge tests were performed at 30 g on reinforced silty sand slopes of 2V:1H inclination representing 7.2 m height using a custom-designed rainfall simulator. The effect of geosynthetic type and optimum position of hybrid-geosynthetic layers within the slope were investigated. The slope movements, pore water pressure profiles, peak reinforcement strains and potential failure surface were analysed with the help of instrumentation and digital image analysis. The slope reinforced with geogrid indicated continuous build-up of positive pore water pressures during infiltration, while, the slope reinforced with hybrid-geosynthetic encountered lesser rise in phreatic levels by around 40% for the same intensity of rainfall. This resulted in substantially lesser peak strains of about 8% in the hybrid-geosynthetic layer as compared to the geogrids and non-woven geotextiles, wherein peak strain values as high as 48% and 19% respectively were registered. As far as the optimum placement of hybrid-geosynthetic inclusions within the slopes are concerned, the hybrid-geosynthetic layers placed within bottom one-third portion of the slope were more effective in drainage function. The hybrid-geosynthetic material thus developed can economize project costs by enhancing the performance of slopes with marginal soil deposits and the use of on-site local soils in reinforced earth construction.

Understanding the soil-root mechanical interaction is crucial to advancing the utilisation of vegetation as a nature-based approach to designing more stable slopes and resilient urban forestry against tree windthrown. Although numerical and analytical models for detailed analysis of soil-root interaction exist, these models are seldom validated due to the lack of field data and the significant challenges in quantifying such interactions due to the complex nature of root system. The centrifuge modelling technique is an effective alternative for unravelling the complexities of the hydromechanical behaviour of vegetated soils by recreating prototype stress levels in small-scale physical models and testing them under more controlled conditions. This work presents a critical review on existing centrifuge modelling methods for vegetated soils, paying particular attention on the (i) fundamentals of centrifuge modelling, where principles, scaling laws and applications relevant to modelling vegetated soils are detailed; (ii) methods for modelling soils, including choice of soil material and sample preparation; and (iii) methods for modelling roots by means of natural plants and root analogues, where the replication of root morphology, mechanical properties and capabilities of modelling transpiration effects are discussed. In every topic, the challenges that could further advance the centrifuge modelling of vegetated soils and the possible ways to address them are highlighted. Finally, the prospect for future studies is discussed, highlighting the potential to enhance the understanding of the underlying mechanisms amongst plant roots, soil, water and external loading.

Plant root-soil mechanical interaction in the application of soil bioengineering such as tree and slope stability has been investigated via centrifuge modelling, utilising root analogues to replicate vegetated soils. Three-dimensional (3-D) printing can be used to model complex root architecture, but the nature of the layer-upon-layer printing process may lead to printed parts of differing tensile behaviour depending on orientation and, consequently, unrealistic simulation of root mechanical reinforcement. This study aimed to assess the strength and stiffness anisotropy of straight root analogues built at varying orientations via three different 3-D printing methods and compare the measured properties with those of real roots. The tensile strength ratios between horizontally- and vertically-printed samples were up to 3.90, 1.27 and 2.57 for fused deposition modelling (FDM), liquid-crystal display (LCD) and Polyjet methods, respectively. Stiffness anisotropy was also more significant in FDM. The relatively higher anisotropy in FDM-printed samples could overestimate the strength and stiffness of most roots in a hypothetical heart-shaped root system, depending on the diameter distribution. Such a physical model may be improved using 45 degrees inclined Polyjet-printed rods.

Landfill failure threatens the safety of surrounding cities and causes soil and water pollution. High water levels can usually spur landfill failure. With the presence of earthquake, landfill instability is triggered in a greater possibility. However, the dynamic response and failure mechanism of landfills with high water level subjected to earthquakes are not yet clearly understood, and relevant experimental studies are quite scarce. This study includes a series of seismic centrifuge tests to investigate the seismic response of the landfill at different water levels. An improved method is proposed to prepare synthetic municipal solid wastes (MSWs) with similar staticdynamic properties to the actual MSWs. The failure and evolution mechanism of landfills with high water levels induced by the earthquake is revealed. Significant transitions are observed in the dynamic response of deformation, acceleration, and pore-water pressure as the water level changes. With the rise of water level, the settlement at the top of the landfill decreases first and then increases, while the horizontal displacement at the toe increases slowly, followed by a sudden drop; the acceleration amplification coefficient in the middle of the landfill increases first and then decreases; the dynamic pore-water pressure gradually decreases from positive to negative, but oscillates at the moderate water level. Three failure criteria and a hydro-earthquake coupled failure limit are proposed to demonstrate the combined effect of water level and earthquake on landfill stability. The test results provide a basis to establish seismic failure standards for landfills with different water levels and guide the seismic instability design of landfills with high water level.