Failure Mechanism of the Bearing Stratum at the End of a Pile Induced by Shield Tunnel Excavation Beneath a Piled Building

Planned tunnel excavation beneath piled buildings is common in actual projects. The excavation-induced deformation of the bearing stratum at the end of an existing pile end may decrease the ultimate bearing capacity of the pile, affecting its mechanical properties. Since previous studies on this topic have focused on the pile deformation induced by tunneling, the deformation mode of the bearing stratum at a pile end has not been thoroughly investigated. In this study, a new two-dimensional failure mechanism describing the failure characteristics of a bearing stratum at the end of an existing single pile induced by shield tunnel drilling beneath the pile is established. Based on this mechanism and the kinematic approach, an analytical equation for the failure surface of the bearing stratum during tunnel drilling beneath a single pile is obtained via a variational principle, and the shapes of the rupture surface of the bearing stratum at the pile end are plotted for various parameters. To validate the validity of the method in practice, an analytical expression for the failure surface of the bearing stratum is obtained and compared with numerical simulation solutions. The results of this comparison show that the presented method is effective for studying the failure characteristics of a bearing stratum at a pile end and can be used for predicting these failure characteristics in practice.