Numerical simulation of ground movements and structural forces in lining for Earth Pressure Balance (EPB) tunneling in clay

Abstract

This thesis describes the development of a 3D finite element model for representing mechanized tunnel construction using an Earth Pressure Balance (EPB) machine in clay. The model uses the commercial FE code, Plaxis 3D, to represent the face pressure, conical shield, grouting process and activation of precast segmental concrete lining systems through a set of boundary conditions that advance through the soil mass along a prescribed trajectory. The model simulates ground conditions associated with on-going EPB tunnel construction for the Crossrail project in central London. The analyses use a linearly-elastic perfectly plastic (MC) soil model based on design profiles of undrained shear strength and stiffness characteristics of London Clay. The analyses show the importance of the in situ Ko-effective stress conditions on predictions of the free-field, short-term (i.e., undrained) ground movements caused by tunnel construction as well as the structural forces induced in the segmental lining. The results of the model are in good overall agreement with simulations from a more complex finite element model that uses sub-structing to represent the EPB machine (Kratos-ekate program; done in collaboration with the research group at TU Bochum). The results of this study form the basis for more extensive research on time dependent ground response and interactions with overlying structures.