The shape characteristics of circular tunnel surrounding rock plastic zone in the complex stress field

• Published in: Arabian journal of geosciences Vol. 15; no. 2
• Main Authors: Hu, Zhiping, An, Xuexu, Li, Fangtao, Zhang, Yonghui
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 2022; Springer Nature B.V
• Subjects: Coefficients; Crystals; Earth and Environmental Science; Earth science; Earth Sciences; Expansion; Mohr-Coulomb theory; Original Paper; Plastic zones; Plastics; Rocks; Shape; Stress; Stress distribution; Tunnels; Underground construction; Tunnel engineering; Plastic zone shape; Circular tunnel; Three-directional planar stress field
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-021-08567-1

To date, few studies have evaluated the influence of adjacent tunnels or large cracks on the rock stress surrounding underground tunnels. In this work, a construction method involving three parallel tunnels was considered, and the influence of the adjacent (left and right side) tunnels on the surrounding rock stress field of the central tunnel was investigated, and a mechanical model of the circular tunnel in the three-directional planar stress field was established. Based on the Mohr–Coulomb failure criteria, the implicit boundary equation at the surrounding rock elastic–plastic interface was derived. Then, the impacts of various stress field proportional coefficients on the shape of the surrounding rock plastic zone around the tunnel were analyzed. The results reveal that when the ratio of the stress field proportional coefficients in different directions is < 2, the plastic zone shape around the tunnel is circular, elliptical, or a rounded rectangle. When the ratio of the stress field proportional coefficients is > 2, the plastic zone around the tunnel is butterfly shaped. In a three-directional planar stress field, the malignant expansion of the surrounding rock plastic zone can occur not only in the 45°, 135°, 225°, and 315° directions from the tunnel (as in the bidirectional stress field), but also in other directions out from the tunnel. With changes in the stress field proportional coefficient, the rock plastic zone surrounding the tunnel can exhibit an asymmetric butterfly-shaped malignant expansion trend. In particular, when the ratio of the stress field proportional coefficients in different directions is > 2, any slight further change can cause significant expansion of the rock plastic zone surrounding the tunnel.