Thermo-mechanical behavior of driven energy piles from full-scale load tests

Abstract

A plethora of studies has been carried out to investigate the thermomechanical behavior of energy piles. However, research associated with full-scale tests on energy piles is still limited. Moreover, the existing full-scale tests are primarily focused on bored energy piles under a certain mechanical load. Very few studies are concerned about driven energy piles or an energy pile under multiple mechanical loads. In contrast to bored piles where the surrounding soils tend to be loosened during construction, construction of driven piles can densify the soils around the piles, and therefore, the responses of the two types of energy piles may be different under thermal load. This study presents a full-scale load test on a driven energy pile under various mechanical loading levels. The pile is a jacked prestressed concrete hollow pile with pile diameter of 0.4 m and length of 15 m. The tests included mechanical load alone, heating-recovery cycles, and cooling-recovery cycles under five mechanical loads. The test results were also compared with previous test results for bored energy pile at the same site. Overall, the results from this study indicated that the level of mechanical loading affected the pile settlement responses under cyclic thermal loading, and the thermal cycle history also affected the rate of pile settlement caused by the mechanical load. Due to the effect of pile construction, the driven energy pile responded differently to the impact of thermal cycles as compared with the bored energy pile.