A load transfer approach for studying the cyclic behavior of thermo-active piles

Unsatisfactory understanding of thermally induced axial stress and mobilized shaft friction in the thermo-active piles has led to a cautious and conservative design of such piles. Despite the fact that the number of construction works using this type of piles has been rapidly increasing since the last 20 years and none of them witnessed any structural damage, the question that still remains is how to overcome the cyclic thermal effects in such piles to optimize the design method. This paper presents a soil–pile interaction design method of an axially loaded thermo-active pile based on a load transfer approach by introducing a proposed t–z cyclic function. The proposed t–z function comprises a cyclic hardening/softening mechanism which is able to count the degradation of the soil–pile capacity during two-way cyclic thermal loading in the thermo-active pile. The proposed t–z function is then compared to a constitutive law of soil–pile interface behavior under cyclic loading, the Modjoin law. Afterwards, numerical analyses of a thermo-active pile located in cohesionless soil are conducted using the two cyclic laws in order to comprehend the response of such pile under combined mechanical and cyclic thermal loads. The behaviors of the pile resulting from the two laws show a good agreement in rendering the cyclic degradation effects. At last, the results permit us to estimate the change in axial stress and shaft friction induced by temperature variations that should be taken into account in the geotechnical design of the thermo-active pile.