A Practical Design Method for Energy Piles Based on Pressuremeter Test Results

This paper aims to propose a design method for energy piles using the results of in situ pressuremeter tests. The method is based on the incorporation of thermal effects through a numerical model of cylindrical cavity expansion. Pressuremeter profiles are generated by the numerical model, which represent the limit pressure at different temperature variations. The pile's bearing capacity is, subsequently, determined by following the standard procedure outlined in Eurocode 7 for the pile design, which is based on pressuremeter tests. Thus, relying on pressuremeter curves, the proposed method is enabled to provide the mobilized base resistance, shaft friction and the bearing capacity of an energy pile. In a second phase, a case study of an energy pile located in a clay soil is conducted in order to explain the different steps of the proposed method and to examine the impact of thermal effects on the bearing capacity. The study reveals an increase of the bearing capacity when heating which reaches 3% at Delta theta = 40 degrees C and a decrease of 4% at Delta theta = - 40 degrees C when cooling. This variation is non-linear and asymmetric because the decrease caused by cooling is not fully recovered during heating: A loss of 1% of the bearing capacity is observed. As a result, it is crucial to consider thermal effects in the design of geothermal piles. On the other hand, the proposed method could be a practical approach for engineers to design energy piles.