Thermo-Hydro-Mechanical Analysis of Geothermal Piles: Implications for Shaft Bearing Capacity

Undrained heating of clays under a non-isotropic stress state represents a worst-case scenario for the stress evolution under field conditions near an embedded heat source, such as in the heating phase in geothermal piles, where the temperature increase may raise pore pressure significantly. Indeed, the increase in pore pressure may be very large and approach shaft friction reduction at the pile-soil interface. To address this, we enhanced a viscoplastic model that was originally developed for rock joints to incorporate non-isothermal conditions to be employed in the THM simulation of shaft bearing capacity of geothermal piles. The developed framework was applied to a full-scale in situ geothermal piles test. The research indicates that with low permeability combined with elevated temperatures, effective stress is significantly reduced in pile-soil interface due to developed excess porewater pressures (pwp).