Analysis of tunnel collapse mechanism due to dislocation and fracture of the surrounding rock block, and a method to predict the collapse height

The boulders formed by cutting the structural surface of the hard rock tunnel may cause instability and disaster during excavation. The Universal Distinct Element Code numerical simulation was carried out based on 64 sets of orthogonal tests for the surrounding rock of the stratified and dislocated block fracture structure. Seven types of collapse modes were obtained for the stratified dislocated crack block structure. Some factors affecting the collapse height were quantitatively analyzed using the range analysis method. Also, six factors influencing the collapse height of a tunnel surrounding rock were ranked. In addition, a collapse height prediction model with six factors was developed for the surrounding rock around the tunnel. In order to analyze the collapse mechanism of the rock mass from the tunnel crack block, six sets of model tests were carried out for a rock mass with block crack stratified dislocation structure. Based on the optical flow method, the progressive evolution process of the rock mass instability induced by tunnel construction was studied, and the characteristics of sequence instability and the influence mechanism of multi-factor coupling of the block group were revealed. The simulation results were verified with the above six groups of laboratory simulation tests, and it was found that the accuracy of the prediction results was higher than 85.21%. It is expected that the results of the present research will provide a scientific basis for predicting, preventing, and controlling the collapse of the surrounding rocks during the construction of tunnels and underground caverns in the block fissure area.