Experimental study of the stability of a tunnel face reinforced by bolts

This paper presents some results of a centrifuge test program conducted in order to study the influence of bolts reinforcement on the behavior of tunnel face in soft ground. A series of four tests was carried out. The results showed the positive influence of bolting on face stability and soil movements. The comparison between test results demonstrated that the tunnel face can be better strengthened by increasing the bolt density. It also showed that a bolt efficient length of about twice the distance between the face and the expected failure surface provides the same reinforcing effect as longer bolts.