Abstract:

In view of a filled karst cave existing on the tunnel vault and based on the limit analysis theorem，a proper failure pattern is established and the specific procedures are deduced to derive the expression of rock plug thickness.Then，the proposed method is adopted to calculate the rock plug thickness corresponding the surrounding rock ranging from levelⅠtoⅤ.The results indicate that with the decrease of surrounding rock strength，the thickness increases continuously.Moreover，applying the method to the engineering projects of Dazhiping Tunnel of the Yichang-Wanzhou Railway，the reasonable results were obtained，which verified the validity of the proposed method.

Key words: karst tunnels, limit analysis theorem, thickness of rock plug, surrounding rock levels