Kinematics of soil arching in piled embankments

The transfer of embankment stresses towards pile heads in piled embankments is attributed to the mechanism known as soil arching. Three-dimensional physical models of piled embankments were built to simulate this mechanism. The progressive settlement of subsoil beneath an embankment was modelled and paused at increments of displacements to allow synchrotron X-ray computed tomography to be performed on the models. Image correlation techniques were then applied to the reconstructed volumes to obtain evolving three-dimensional displacement and strain fields. The strain fields show localised (shear bands) and diffuse failure modes occurring above pile heads within the embankment fill. These failure surfaces are seen to progressively develop as the subsoil undergoes settlement. The displacement fields also show the formation of a plane of equal settlement developing at a height above the pile heads, known as the critical height. The critical height is dependent on the height at which the failure surfaces propagate into the embankment fill, and a method is proposed to calculate the maximum height of failure surfaces based on the observed kinematics. The full-field kinematics provide fundamental insight into the soil arching mechanism that develops within piled embankments.