Estimation of Mechanical Characteristics of the Ground Ahead of a Tunnel Face

In order to identify the mechanical parameters of the ground ahead of a tunnel face, a three-dimensional back-analysis method is newly proposed. The method consists of a three-dimensional finite element analysis and the secant method, and is based on an iteration procedure. The Poisson's ratio, the modulus of elasticity and the six components of the initial stress levels of the ground around a tunnel face are back analyzed from displacements obtained by field measurement, which are produced by one-step excavation of the tunnel face. Influence of measurement errors of field displacements on accuracy of the results identified is made clear through numerical calculation.