Analytical Solution for Bolted Tunnels in Expansive Loess Using the Convergence-Confinement Method

Abstract

Ground reinforcement using bolts is effective for underground excavations. The ground response of expansive loess tunnels with bolt reinforcement remains poorly understood. Therefore, this paper proposes an analytical solution for bolted rock in expansive ground using the convergence-confinement method. On the basis of the bilinear strength criterion for rock mass, a computational procedure was used to obtain the ground reaction curve (GRC) for expansive loess tunnels with bolt reinforcement. The proposed approach considers ground expansion stress and geometrical parameters, mechanical parameters, and pretension of bolts. The results confirm the positive influence of bolt reinforcement and the negative influence of expansion stress on the GRC. Bolt reinforcement offers good resistance against harmful expansion stress and improves the overall stability of loess tunnels. When the expansion stress of an expansive loess tunnel reaches a certain limit, bolt reinforcement is necessary for tunnel stability. This critical limiting value of the expansion stress can be evaluated using the proposed approach. The proposed analytical solution provides guidelines for the stability estimation of tunnel excavations in expansive ground.