Abstract:
Geothermal energy piles are becoming more common but there is still limited guidance for analysis and design of such piles. Many engineers may be uncertain as to how or even whether energy loops, for example made with High-Density Polyethylene (HDPE), influence the geotechnical performance of a geothermal energy pile. In this research, numerical simulations and parametric studies were performed, utilising the finite element method, to determine how variously configured HDPE loops influence the bearing capacity and settlement of a pile. With the aid of PLAXIS 3D finite element software to model and simulate 60 geothermal energy piles having differently configured HDPE loops, it was found that, for a typical 2 m diameter pile, 11 HDPE tubes caused the pile capacity to decrease by as much as 70% when compared to a conventional pile. However, with 3-4 HDPE loops, it was found that the pile load capacity was enhanced by 30%-75%, suggesting the existence of an optimum reinforcing effect of HDPE loops on the soil. It was also found that reduction of pile capacity due to embedded HDPE loops in the vicinity of a pile base was accompanied by reduction of pile stiffness hence increase in settlement for a given applied load.
Therefore, conventional soil mechanics-based formulae for calculating pile base resistance and settlement may be inappropriate for geothermal energy piles and a more careful approach, such as numerical modelling and field testing is needed. There was confidence in the results of this research because: (a) the simulated settlements for the ultimate pile capacities were approximately 10% of the pile diameter, which is consistent with findings from field pile tests, (b) the simulated pile capacities for piles without HPDE loops were found to be consistent with estimates from soil mechanics-based formulae.