Face stabilisation of shallow tunnels using fibreglass dowels

Abstract

Stability of the excavation face in shallow tunnels and in poor ground is at present a relevant problem in tunnelling. Even though face reinforcement with fibreglass dowels has proved to be efficient, there is still no reliable routine design method available. A new calculation procedure is illustrated in this paper for the analysis of face reinforcement with fibreglass dowels in shallow tunnels. The procedure is based on the limit equilibrium method (LEM) applied to the ground core ahead of the face, and it is able to offer a detailed evaluation of the interaction between each reinforcement element and the surrounding ground. The main result of the calculation concerns the safety factor of the excavation face with dowel reinforcement. Based on this safety factor, it is possible to identify the appropriate length and number of dowels. The procedure has been applied to two real cases, and satisfactory results have been obtained.