The thermo-mechanical (TM) behaviour of the energy pile (EP) group becomes more complicated in the presence of seepage, and the mechanism by which seepage impacts the EP group remains unclear.In the current work, a 2 x 2 scale model test bench of EP group was set up to investigate the TM behaviour of EP group with seepage. The test results indicate that the heat exchange performance of EP group with seepage can be significantly enhanced, but also leads to obvious differences in the temperature distribution of pile and surrounding soil along the seepage direction, and thus causes evident differences in the mechanical properties between the front pile and the back pile in pile group. Compared with the parallel connection form, the thermal performance of EP group with the series connection form is slightly attenuated. However, the mechanical properties of various piles in the EP group differ significantly. Under the action of seepage, the mechanical balance properties of various piles in the forward series form are optimal, followed by the parallel form, and the reverse series form is the least optimal. A 3-D CFD model was established to further obtain the influence of seepage and arrangement forms on EP group. The findings indicate that seepage can not only mitigate thermal interference between distinct piles but also expedite the process of heat transfer from pile-soil to reach a state of stability. Concurrently, the thermal migration effect induced by seepage will be superimposed along the seepage direction, resulting in the elevation of thermal interference of each pile along the seepage direction, and the superposition of thermal migration effect increases with the time. Under the same seepage condition, the cross arrangement can enhance the thermal performance of EP group, optimize the temperature distribution of pile and soil, and thus the imbalance of mechanical properties among pile groups can be reduced. In addition, the concepts of thermal interference coefficient and heat exchange rate per unit soil volume are introduced to facilitate a more precise evaluation of the thermal interference degree of each pile in the pile group and the heat exchange performance under different pile arrangement forms.The standard deviation and mean value in the statistical method are used to evaluate the equilibrium of mechanical properties of pile group, which is more intuitive to compare the differences in mechanical properties of pile groups under different working conditions.

An indirectly coupled model, integrating the Richards' equation, the diffusion wave approximation equation, and the Green-Ampt infiltration model, has been developed to efficiently analyze surface flow and groundwater seepage under heavy rainfall conditions. Model effectiveness was validated through rigorous soil column and slope model experiments. Using this model, the sensitivity of slope stability to rainfall intensity and soil permeability heterogeneity was investigated utilizing local factor of safety (LFS) analysis. Increased rainfall intensity was found to notably impact slope stability, while the influence of permeability anisotropy on stability varies with slope steepness. This method was subsequently applied to analyze the slope stability of a soil heritage site impacted by extreme precipitation during Typhoon Lekima. Preliminary comparisons revealed that the steady-state average infiltration rate, when surface runoff was considered, was higher than the rate computed without it. Additionally, potential hazard zones were identified near areas with maximal water accumulation and runoff velocity when surface runoff was considered. Building on these findings, LFS changes were evaluated at various locations during and after 20 h of rainfall. The study indicated decreased stability in the shallow layer during rainfall, with slight improvement in the deeper layer. Post-rainfall, the shallow layer stability recovered, whereas the deeper layer stability declined due to increased depth of rainwater infiltration. The results suggest that the indirectly coupled model, combined with LFS analysis, is a robust method for effectively evaluating shallow layer stability of slopes in extreme rainfall conditions.

Saturation development and distribution at the soil-bedrock interface are important for predicting shallow landslide occurrence. Previous studies have indicated that saturation is generated in bedrock depressions and valleys and that bedrock groundwater seepage generates locally saturated areas. However, the effects of soil permeability, which is known to be heterogeneously distributed, on saturation development and distribution are poorly understood. In this study, we performed unprecedented high-resolution (approximately 50 cm grid) soil pore water pressure and soil temperature monitoring using 141 tensiometer-thermocouple sets in a plot measuring approximately 5 x 4 m to investigate the effects of topography and bedrock groundwater seepage on saturation development and distribution. We then measured permeability distribution of two soil profiles, including at the soil-bedrock interface, using the Guelph Permeameter method (GP method) for comparison with saturated zone distribution and saturation duration. The results indicated that a perennial saturated area was formed by bedrock groundwater seepage and was distributed downstream from a certain bedrock surface altitude in the lower region of the study plot. After a peak of rainfall, the perennial saturated area expanded upslope owing to the increased seepage. In areas without the influence of bedrock groundwater, saturation was observed to retreat rapidly at high permeability points and persist over long periods at low permeability points; however, the saturation duration was inconsistent with the bedrock surface topography. Therefore, it is suggested that the bedrock altitude controls the saturation distribution generated by bedrock groundwater, whereas the distribution of saturation that is associated with direct rainwater infiltration may be controlled by the permeability distribution during recession periods. Although the plot size was small, the unprecedented high-resolution observations suggest that the permeability distribution, rather than the bedrock topography, may control the saturated zone distribution following rainfall.

Suspended waterproof curtains combined with pumping wells are the primary method for controlling groundwater levels in foundation pits within soft soil areas. However, there is still a lack of a systematic approach to predict the groundwater drawdown within the foundation pit caused by the influence of these suspended curtains. In order to investigate the variation of groundwater level within the excavation during dewatering processes, the finite difference method is employed to analyze the seepage characteristics of foundation pits with suspended waterproof curtains. Basing on the concept of equivalent well, this study examines the coupled effects of aquifer anisotropy (ki), aquifer thickness (Mi), well screen length (li), and the depth of waterproof curtain embedment on the seepage field distortion. A characteristic curve is established for standard conditions, which exposes the blocking effect of the curtain on the amount of groundwater drawdown in the pit. Additionally, correction coefficients are proposed for non-standard conditions, which, in turn, results in a prediction formula with a wider range of applicability. Comparative analysis between the calculated predictions and the field observation data from an actual foundation pit project in Zhuhai City validates the feasibility of the quantitative prediction method proposed in this research, which also provides a 21% safety margin.