The Stability of Shallow Tunnels

摘要

Tunnel pressures necessary for the support of shallow tunnels and underground openings in soft ground have been estimated using the limit theorems of plasticity. Two of the situations considered have been special cases of the idealization suggested in the introduction for the process of constructing a shallow circular tunnel using a shield or tunnelling machine. The results indicate that higher tunnel pressures are required for stability of the unlined circular tunnel than for the circular tunnel heading. The stability ratio N, originally proposed by Broms and Bennermark has provided a convenient framework for interpreting the results and can be used to estimate tunnel pressures required for stability. In contrast to Broms and Bennermark, however, the results presented here indicate that the critical values of N show a marked variation with the depth of burial of the tunnel.