Axial pull-out response of a small-scale concrete pile subjected to cyclic thermal loading in sand

Abstract

Energy piles support structural loads and exchange heat with surrounding soils using closed-loop ground source heat pump (GSHP) systems. A GSHP connected to an energy pile operates in cycles where it functions for a period of time (running time) then stops for another period of time (stoppage time). This intermittent operation of the GSHP subjects the piles and surrounding soil to changes in temperature and to temperature cycles introducing challenges to foundation design. The research presented in this paper focuses on evaluating the effects of thermal cycles on the soil temperature and soil-pile interaction. In order to investigate these effects, an instrumented concrete energy pile with diameter of 101.6 mm and length of 1.383 m was subjected to different thermal cycles and tested under pull-out loading at the soil-structure interaction (SSI) facility at Lehigh University. In this paper, results from two pile tests are presented. Axial pull-out response of a pile subjected to five thermal cycles was compared to the response of a pile subjected to pull-out loading at room temperature. It was observed that the pile subjected to thermal cycles had an ultimate shaft resistance that is 28% greater than that of the pile tested at room temperature.