Visco-elastic Analysis of Effect of Weak Layer on EDZ around a Tunnel

Significant deformation was found at the vicinity of weak layers in an old tunnel. This indicates understanding of effect of weak layers on the deformation is important for design of a tunnel. In this study, extension of EDZ around a tunnel was estimated by visco-elastic analysis. Then, analytical results were qualitatively compared with EDZ estimated by RQD. Analytical results showed that EDZ extended toward the more effective weak layer after developing around sidewalls. They also showed that extension of EDZ depended on dip and location of weak layers. Gentle weak layer below the tunnel influences more than that above the tunnel. Steep weak layer above the tunnel influences more than that below the tunnel. RQD distribution showed that EDZ extended toward vertical direction and upper gentle weak layer was more effective than lower one. This is not good agreement with the analytical results. The effect of ratio of horizontal stress to vertical one on extension of EDZ was analyzed. The result at the ratio of 3.0 was qualitatively good agreement with that by RQD. This indicates that the stress ratio affect EDZ as well as dip and location of weak layers.