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Nowadays, the energy pile system is considered one of the structures’ energy supply systems through geothermal renewable energy in developed countries. Although various studies have been carried out to analyze the behaviors of these systems, very few laboratory studies are reported in the literature. The present study aims to evaluate the behavior of small-scale energy piles using laboratory and numerical models in Babolsar sand soil. The presented physical modeling was accurately designed and carried out by the Geotechnical Research Group of the Babol Noshirvani University of Technology. Studies were conducted under different thermal loading conditions. The results indicated that an increase in heating time made the temperature difference in places farther from the pile more tangible. On the other hand, the values of free thermal expansion of the pile head are almost the same under different thermal loading conditions. Also, in applying a mechanical load of 200 N on the pile head, the displacement of the pile head was reduced by approximately 15% compared to the condition without mechanical loading. It is worth noting that most of the heat dissipation was radial in the soil environment around the pile. The range with a distance of approximately 2D from the central axis of the pile was considered as the area being significantly affected by the soil temperature around the pile, such that the amount of temperature changes was greater than 50% of the increased pile temperature in this area. Next, the heat injection rate and the pile and soil thermal resistances were also determined using the determined temperature gradients. Finally, the test results were confirmed by numerical modeling.

Energy piles serve as load-bearing foundations that facilitate sustainable heat exchange with shallow geothermal energy by integrating geothermal heat exchangers (GHEs). Nonetheless, the thermal loading introduces the potential for expansion and contraction in energy piles, which can impact the soil-pile interaction. Since the majority of the experimental research on energy piles only considered the heating load, investigating the thermomechanical response and bearing capacity of energy piles under cooling and different end-support conditions remains an area that requires more elaboration. To address this, two series of experiments were performed on a concrete energy pile using 1 gphysical modeling in dry sand with a relative density of 48 %. The tests were conducted on semi-floating energy piles (SFPs) and end-bearing energy piles (EBPs) under monotonic cooling while varying the average pile temperatures (a total of 6 tests). The results indicated that the EBP's behavior under cooling load was similar to SFP's. The bearing capacity alterations of the pile were calculated by determining the maximum thermomechanical stress induced in each of the conducted tests. The experimental results revealed that the bearing capacity of SFP was more significantly affected during a cooling load than EBP. Specifically, under identical mechanical loading conditions, the maximum reduction of the bearing capacity of SFP and EBP was found to be 13.4 % and 5.5 %, respectively. This phenomenon can be attributed to the distinction in load transfer mechanisms between the two foundation types, where a decrease in frictional shaft resistance had a more noticeable impact on reducing the bearing capacity of SFP compared to EBP. A comparative analysis was also conducted among settlement, axial stresses, and mobilized shaft friction values induced by various loading types.

This paper establishes an analytical correlation between factor of safety (FS) and reliability index βvalues commonly used in the design of drilled shafts in sand. This is achieved through fragility analysis of unit shaft and base resistances, calculated using finite element analysis-based capacity calculation equations, for drilled shafts. Analytical fragility curves are developed for allowable unit resistances along the pile shaft and at the pile base. Developed fragility curves are used to map FS values with corresponding values of β. Such analytical FS–βcorrespondence is not well established in literature. Comparison of results from fragility analysis with those obtained through conventional Monte Carlo simulations reveals excellent agreement. Developed FS-βcorrelation is employed in reliability analysis to estimate load and resistance factors corresponding to different FS values. Evaluated load and resistance factors compare very well with AASHTO specifications.

The prediction of coupled nonisothermal multiphase flow in porous media has been the subject of many theoretical and experimental studies in the past half a century. In particular, the evaporation phenomenon from the shallow subsurface has been extensively studied based on the notion of equilibrium phase change between liquid water and water vapor (i.e., instantaneous phase change). One of the frequent assumptions in equilibrium phase change approach is that liquid water is hydraulically connected throughout the vadose zone. Furthermore, classical soil‐water retention curves (e.g., van Genuchten model), which have been extensively used in the literature to model evaporation process, are only valid for high and intermediate saturation degrees. Although these limitations have been addressed and improved in separate studies, they have not yet been rigorously incorporated in the numerical modeling of nonisothermal multiphase flow in shallow subsurface of in‐field soils. Therefore, the aim of this study is to investigate the coupled heat, liquid, and vapor flow in soil media through the Hertz‐Knudsen‐Schrage (HKS) phase change model and by incorporating a water retention model which captures the soil‐water characteristics from full to oven‐dried saturation degrees. A numerical model is developed and validated against the in‐field experimental data. Reasonable agreements between the calculated and measured values of water contents at all depths, as well as the temperature, and cumulative evaporation are observed. Results also confirm that the contribution of the film flow in overall mass flow in the medium is required for accurate modeling and cannot be ignored. Nonequilibrium phase change is dominant for the very shallow subsurface soil with respect to dynamic variations of atmospheric demandFilm flow and a general SWR curve are necessary to model wetting/drying cycles for a wide range of moisture contentConsidering film flow in hydraulic conductivity of soil plays a significant role to model wetting/drying cycles in low saturation degree