Model test study of punching shear failure mode of the bearing stratum induced by tunneling beneath an existing pile

Abstract

With the increase of the density of subway line in big cities, it is common for newly built shield tunnels to cross beneath the existing pile foundations at short distances. When the disturbance generated during the construction of the shield tunnels is transmitted to the bearing stratum of the existing pile tip, a punching shear failure may occur in the bearing stratum. To study the evolution process and final form of the punching shear failure of the bearing stratum, a scaled model test based on the Particle Image Velocimetry (PIV) technology is designed. By using PIV technology to analyze deformation images of the bearing stratum, the failure range and shape of the bearing stratum between the pile tip and tunnel induced by excavation are obtained. Using the failure shape of the bearing stratum provided by the model test, a theoretical failure mechanism based on the spatial discretization technique is constructed. The limit analysis theorem is employed here to calculate the theoretical solution of the punching shear failure surface of the bearing stratum. The good agreement of the failure range for the bearing stratum between the model test and theoretical result indicates that the model test presented here is effective.