A Study of the Mechanical Properties of Middle-Rock-Wall and Preliminary Lining of a Shallow Large-Span Tunnel with Small Interval

Abstract

Mechanical properties such as stress, deformation, and plastic zone distribution of the middle-rock-wall, along with the mechanical characteristics of the preliminary lining under different spacings, are particularly important for guiding the design and construction of small spacing tunnels. A three-step excavation numerical analysis model of the tunnel excavation is established, simulating the following conditions: D/B=0.5, 0.75, 1, l.5, l.25, 2. The mechanical behavior of a middle-rockwall was analyzed after multiple disturbances through the digging of another tunnel. The stress and deformation analysis of the middle-rock-wall changes resulting from different intervals showed that when the middle-rock-wall thickness is less than 0.75B, the plastic zone expands rapidly and connects to the upper part of the middle-rock-wall. This result indicates that the latter digging of the tunnel has great influence on the force and deformation of the middle-rock-wall and on the force of the initial structure of the advanced tunnel. Under the unfavorable situation of D/B=0.5, grouting can be used to reinforce the middle-rock-wall; furthermore, grouting can also greatly reduce initial support force and improve the stability of the surrounding rock. Analysis results further show that the maximum axial force can be reduced by 49.l%, and that the maximum bending moment can be reduced by 29.l%. Thus, the stability of the surrounding rock is greatly improved through grouting reinforcement.