Collapse mechanism and support pressure for shallow tunnel face

The stability of shallow tunnel face is simplified into a two-dimensional problem, and the corresponding collapse mechanism is proposed. The collapse mechanism is composed by a series of rigid blocks with its corresponding velocity field which is characterized by change of velocity vectors from vertical to nearly horizontal in front of the tunnel face. Based on the geometrical relations of the collapse mechanism, constrains of optimized variables for the collapse mechanism are established according to the object function of the shallow tunnel face support pressure, obtained after deducing geometrical parameters of collapse mechanism and velocity field needed for latter calculation. The computer program has been compiled using Matlab software, which can be used to solve the mathematic optimization problem. Finally, results for various conditions of support pressure needed for the stability of shallow tunnel face and optimized collapse mechanisms and corresponding velocity fields are also obtained. The factors that will influence the stability of shallow tunnel face are analyzed.