Geomechanical Substantiation of Soil Stability During Tunnel Construction by Shield Tunneling Complexes in Layered Massifs

This paper presents the development and results of an analytical method for calculating the stability coefficient of a rock mass that is capable of adjusting the face support pressure required for face stability depending on changes in the mass structure at the tunnel face. The analytical relationships presented in this work are based on the simulation of 225 three-dimensional finite element numerical models. The influence of the mass structure at the tunnel face was examined by varying the thickness and position of the layer at the tunnel face, as well as its stiffness and strength parameters. The maximum difference in the values of the main monitored criteria exceeded 85% for such indicators as the area of the surface settlement trough, the area of the zone of negative vertical deformations, the width of the settlement trough, and the maximum value of vertical settlements. This study proposes a practical implementation of the developed analytical method—a stability coefficient of the soil mass was developed to adjust existing analytical relationships when a soil layer with mechanical characteristics differing from the host mass is present at the tunnel face.