Numerical study on the thermal-induced mechanical behavior in deep energy diaphragm wall (EDW): The long-term soil elastoplastic effects

摘要

? 2022 Elsevier LtdThe energy diaphragm wall (EDW) attracted increasing attention due to its high energy exchange rate and low space occupation. The current research on EDW primarily focused on its heat exchange capacity and performance. The elastoplastic effects on thermal-induced mechanical behavior caused by soil were neglected, which might underestimate the wall deflections in deep EDW due to the asymmetrical surrounding pile height pressure on both sides. This paper investigated the thermal performance and the induced mechanical behavior in deep energy diaphragm wall (EDW) based on the finite element analysis method (FEA) by the COMSOL Multiphysics software. Firstly, the thermal performance of varied pipe configurations (e.g., single U-shaped; W-shaped; double-U shaped; horizontal arrangement) was studied. Then it was followed by a study of a single heating–cooling cycle with a single U-shaped pipe, where the elastoplastic impact of the soil in the deep EDW was observed. Moreover, a parametric analysis with a long operation period (30 years) perspective was proposed regarding the heat load modes, the pipe buried locations, the air temperature of the adjacent underground space, and the excavation level. Results revealed that the heat transfer process caused an obvious impact on thermal-induced mechanical behavior. Higher levels of heat injection (Case 3) and extraction (Case 2) both led to a relatively large wall deflection after 30 years. The horizontal displacements at the top of the wall under Case 3 and Case 2 were up to 30.5 mm and 25.9 mm, respectively, while 22.9 mm under balanced case (Case 1) and 21.1 mm under the no heat load case (Case 0). When the pipe was close to the side of the excavation, the plastic deformation was about 1.25 times greater than that on the soil side, where the thermal contraction effects were emphasized. Besides, the air temperature in the underground space caused a small impact on the plastic strain in the soil domain. Because of the enhancement in the heat transfer process from the air to the wall while the air temperature increased, resulting in the average wall temperature raised. In addition, the influence caused by the excavation levels was quite evident. The deeper the excavation level, the easier the plastic strain to occur. This paper proposed a new perspective for understanding thermal-induced mechanical behavior in deep EDW, especially the long-term soil elastoplastic effects, which exerted a complex impact on the deformation variation of the diaphragm wall.