Energy-based prediction of volume loss ratio and plastic zone dimension of shallow tunnelling

Abstract

This paper presents an analytical method using energy conservation to predict ground movements due to shallow tunnel excavation. In our method, a Nephroid curve is innovatively used to outline the plastic zone produced by shallow tunnelling. Both the volume loss ratio and the plastic zone dimension can be calculated. We classify the development of plastic zone into three stages based on the plastic zone characteristics: (1) Initiation and growth of plastic zones; (2) Coalescence of plastic zones; and (3) Plastic zones extending to surface. The proposed method is verified using the finite difference method. Our proposed method is successfully used in an engineering project. The effects of the plastic zone, overburden depth, tunnel radius, soil elastic modulus, soil shear strength, and boundary conditions on the volume loss ratio, the plastic zone dimension, and the maximum surface settlement are investigated.