Experimental investigations of the thermo-mechanical behaviour of an energy pile with groundwater seepage

Abstract

• A set of small-scale model experimental device of energy pile with the groundwater seepage is built. • Influences of groundwater seepage on thermo-mechanical behaviour of energy pile are investigated. • The performance comparison between the energy pile in dry sand and saturated sand are conducted by tests . Energy pile with groundwater seepage usually exhibits more complex thermo-mechanical behaviour than that without groundwater seepage because of the existence of seepage field and the interaction between thermal, mechanical and water flow. The paper conducted laboratory small-scale tests to obtain the thermo-mechanical behaviour of energy pile with groundwater seepage. The influences of seepage velocities, groundwater levels, dry sand and saturated sand on the heat exchange performance, pile and soil temperatures, pile head displacement, pile thermal strain and pile tip soil pressure are experimentally investigated. The results illustrated that it is meaningful to place energy pile in the soil with a large seepage velocity to improve the heat transfer performance and temperature recovery rate of pile and soil, and thus the temperature change of pile and soil, pile thermal strain, pile head displacement and pile tip soil pressure can also be effectively alleviated, which is beneficial for the stability and safety of the pile structure. The groundwater level determines the contact area between the pile body and seepage field. The rise of the groundwater level is conducive to the improvement of the heat transfer performance of energy pile and the natural recovery of pile head displacement during the 14 h recovery, but it will also produce a larger pile head displacement during 10 h operation. Compared with the dry sand, the heat transfer rate of energy pile in the saturated sand is about 3.19 times that in dry sand, and the variation amplitude of pile and soil temperature, pile thermal strain, pile tip soil pressure can also be effectively reduced. However, the change value of pile head displacement in saturated sand during the operation and recovery is greater than that in dry sand, and the residual pile head displacement in saturated sand after 14 h of recovery is lower than that in dry sand. In addition, the increase of groundwater level and soil saturation will cause the pile body friction to decrease, which can be used to explain the reason for the changes in pile head displacement.