Progressive Collapse Mechanism and Safety Control of Deep Buried Tunnel Vault in Soft and Broken Surrounding Rock

Tunnel vault collapse is the main type of tunnel accident that has brought huge injuries and deaths, and the causes and prevention of tunnel vault collapse have aroused great concern. To solve the safety problems of tunnel vault collapse, the occurrence mechanism and evolution law are investigated. Using the upper limit variational method, the collapse prediction model of tunnel vault in deep overburden ground is developed, and the prediction curve of tunnel vault collapse range is derived. Considering the progressive collapse characteristics of deep buried tunnel vault in weak and broken surrounding rock, the whole process curve of the progressive collapse range is derived and compared to the model test results. Furthermore, the control principle and bearing mechanism of tunnel collapse with pre-control and process control measures are respectively clarified. The method to determine the surrounding rock load of support measures is proposed. The following results are found. The width of tunnel collapse increases with initial cohesion and uniaxial tensile strength, however, it decreases with weight and the nonlinear coefficient. The height of Tunnel collapse increases with tensile strength and nonlinear coefficient, and it decrease with initial cohesion and weight. Considering the multiple attenuation of cohesion and tensile strength of surrounding rock, the prediction curve of progressive collapse of tunnel vault is in good agreement with the characteristics of model test. The control measures of vault collapse can be divided into pre-control and process control considering control mechanism and objectives. The ratio of deformation load to collapse load increases with initial stiffness coefficient and original rock stress, decreases with collapse height and elastic modulus, and is little affected by tunnel radius and Poisson’s ratio. Both deformation load and total load of surrounding rock increase with the increase of collapse load. © 2022 Editorial Department of Journal of Sichuan University. All rights reserved.