Stress analysis of reinforced tunnel faces and comparison with the limit equilibrium method

摘要

The present paper investigates the stability of reinforced tunnel faces in dry cohesive-frictional soils by means of 3D numerical stress analyses which take account of the individual bolts. The numerical calculations are performed assuming an elastic, perfectly plastic material obeying the Mohr-Coulomb yield criterion. As usual in this kind of problem, the bolts are modelled by one-dimensional tension elements, which have zero diameter and cannot take into account geometrically the diameter of the bolts or the borehole. The first part of the paper deals with the approximations induced by this simplification. More specifically, the paper shows by means of numerical pullout tests in respect of a single bolt in elasto-plas-tic soil that the behaviour of this model depends significantly on the fineness of the numerical mesh. The second part of the paper investigates the reinforcing effect of bolts on face stability assuming that the bond strength of the bolts depends on the confining stress with strength parameters equal to those of the soil. For several bolting patterns, the minimum cohesion c'_(lim) needed for face stability is calculated iteratively and compared with the predictions of the limit equilibrium method of Anagnostou and Serafe-imidis (2007).