Energy piles, which serve the dual functions of load-bearing and geothermal energy exchange, are often modeled with surrounding soil assumed to be either fully saturated or completely dry in existing design and computational methods. These simplifications neglect soil saturation variability, leading to reduced predictive accuracy of the thermomechanical response of energy piles. This study proposes a novel theoretical framework for predicting the thermo-hydro-mechanical (THM) behavior of energy piles in partially saturated soils. The framework incorporates the effects of temperature and hydraulic conditions on the mechanical properties of partially saturated soils and pile-soil interface. A modified cyclic generalized nonlinear softening model and a cyclic hyperbolic model were developed to describe the interface shear stress-displacement relationship at the pile shaft and base, respectively. Governing equations for the load-settlement behavior of energy piles in partially saturated soils were derived using the load transfer method (LTM) and solved numerically using the matrix displacement method. The proposed approach was validated against experimental data from both field and centrifuge tests, demonstrating strong predictive performance. Specifically, the average relative error (ARE) was less than 15% for saturated soils and below 23% for unsaturated soils when evaporation effects were considered. Finally, parametric analyses were conducted to assess the effects of flow rate, groundwater table position, and softening parameters on the THM behavior of energy piles. This framework can offer a valuable tool for predicting THM behavior of energy piles in partially saturated soils, supporting their broader application as a sustainable foundation solution in geotechnical engineering.

The shear deformation characteristics of the pile-soil interface is significantly influenced by the water content due to the structural strength and water-sensitive nature of loess, leading to strain-softening behavior during shear deformation. Effective saturation and Bishop's effective stress were employed as direct driving variables to reflect the effects of saturation on the structural strength of loess, based on the water-stress coupling characteristics of the pile-loess interface. Structural parameters such as cohesion, friction angle, and compression index, along with their evolution equations, are developed to reflect the degradation of structural strength with plastic strain and effective saturation. On the basis, by equating the plastic deformation of unsaturated structural loess with saturated non-structural loess under lateral confinement, a load-collapse function is developed for the pile-loess interface in the effective stress-effective degree of saturation space. An elastoplastic hydro-mechanical coupling model for the pile-loess interface is developed by integrating a soil-water characteristic curve. The model is validated using direct shear test data from unsaturated structural Lanzhou loess and field pile test data from Shanxi unsaturated loess. The results show that the proposed model effectively. represents the hydro-mechanical coupling behavior of the pile-unsaturated loess interface, reflects the effects of saturation on shear strength, and captures the variation of strain-softening characteristics at the pile-soil interface with saturation. The model offers aneffective approach for disaster prevention design, analysis, and assessment of the load-carrying behavior of piles in unsaturated loess.

Soil arching is a critical mechanism in understanding the soil-pile interaction of pile-reinforced soil slopes. Previous research primarily focuses on evaluating the arching behavior under static loading conditions, whereas the seismic response of soil arching under earthquake loading remains unclear. This paper aims to investigate the seismic arching behavior in pile-reinforced soil slopes through a series of reduced-scale shaking table tests. The soil deformation characteristics, distribution of dynamic earth pressures, and internal forces of piles were systematically analyzed to evaluate the geometry characteristics and load-transfer ability of soil arching with varying input peak ground acceleration (PGA), pile spacing, and relative density of soils. The results indicate that soil arching that grew in either a wider pile spacing or loose sand tended to fully develop under low input PGAs and exhibited a higher arching height. Following this, a practical model was proposed to predict the stable arching height. With increasing the input PGAs, the seismic arching behavior involved four stages, termed stable, transitional, meta-stable, and failure. The load-transfer ability and seismic response of piles under earthquake loading were dependent on the pile spacing and relative density of soils. A wider pile spacing gave rise to a greater load-transfer ability which was enhanced in the stable arching stage and then diminished in the subsequent stages, showing a different trend from closer pile spacings. Compared to medium dense sand, loose sand reduced the load-transfer ability, but it promoted the occurrence of stable arching and elevated the point of dynamic load application. Furthermore, in the arching failure stage, arching footholds played a crucial role in maintaining slope stability as their instability directly resulted in overall slope failure. These findings are of practical significance for the design and construction of soil slopes reinforced with piles.

The construction of tunnels excavated by the conventional method in densely populated urban environments requires an adequate characterization of the loads acting on the primary lining during the excavation process, to ensure that the ground is deformed and stresses around the tunnel are relieved, simultaneously complying with the failure and serviceability limits of international standards while minimizing damage to nearby structures. In this paper, common lining design criteria are revisited, through the numerical simulation of an instrumented tunnel which is part of a 4.5 km long metro line currently under construction in Mexico City. Key needs for improvement in current design approaches are identified. The tunnel was instrumented with load cells, extensometers, and topographical references for convergences and divergences. A three-dimensional finite difference model of the instrumented was developed, and the load transfer mechanisms between the excavated soil and the primary lining were analyzed. Then, the numerical simulation of the contribution of the secondary lining in the overall stability for sustained load was established, along with the expected ground settlements, which can significantly affect nearby structures. Results gathered from this research are key for updating lining design criteria for urban tunnels built in stiff brittle soils.