Pile groups under deep expansion: a case history

Abstract

A viaduct in a high speed railway line experienced severe heave of its central pillars as a result of deep expansion of an anhydrite rock. Bridge pillars were founded on pile groups which experienced vertical heave displacements as well as lateral displacements and rotations. A semi-analytical solution for the response of a pile group under loading and arbitrary located soil expansion was developed integrating fundamental solutions for the elastic half-space. The procedure was first validated and then applied to explain the recorded behaviour of the pile groups. The deep expansion was identified from independent surface heave and continuous extensometer readings. Group rotations were well predicted. Observed tensile fissures at the cap-pile contact were explained by the calculated forces and moments on the piles.