Mechanical characteristics analysis of surrounding rock in deep buried tunnel in karst regions

A theoretical model was set up for analyzing the mechanical characteristics of the surrounding rock in karst-tunnel system, and Schwarz's alternative method was employed to derive the analytic solutions for the stress and deformation of the surrounding rocks upon excavating deep buried tunnel under the existing karst conditions. Taking Qiyueshan railway tunnel for example, the analytic results of the mechanical characteristics of surrounding rock were compared with finite element numerical results, which validated the correctness of the process for deriving the analytic solutions of the model. Analysis results show that karst cave results in bias pressure phenomenon to the surrounding rock during tunnel excavation process. There is obvious vertical stress concentration at the surrounding rock near karst cave, and there is little difference between the horizontal stresses of two sides. Greater horizontal displacement occurs to the surrounding rock near karst cave. The ratio of the maximum values between two sides of tunnel is about 1.7. With the increasing of the clear distance between tunnel and karst cave, the bias pressure of surrounding rock weakens gradually. The effect of karst cave on the surrounding rock in deep buried tunnel can be neglected when the clear distance between tunnel and karst cave is greater than 1.5 times of cave diameter.