Research On The Wedge Failure Mechanisms Of Rock Slopes Based On Three-dimensional Discontinuous Deformation Analysis

The stability of rock slopes is one of the most important and challenging issues in the field of rock mechanics and engineering.The common failure modes of rock slopes are planar failure,toppling failure and wedge failure.Wedge failure usually occurs in a wider range of geological and geometric conditions.This thesis mainly focuses on the key scientific problem of wedge failure and its disaster mechanisms of rock slopes.Based on the improved critical sliding model of wedge joint surface,the three-dimensional discontinuous deformation analysis(3D DDA)method for slope wedge failure is developed,and the analytical solutions are derived by combining the wedge stability theory.The failure and migration processes of slope wedges are studied,and the failure mechanisms,movements,disaster processes and laws of slope wedges are revealed.The main contents of this thesis are as follows:Based on the theoretical formulas of wedge stability analysis of rock slopes,the analytical solutions are compared with the numerical simulation results of 3D DDA,which can verify the reliability of 3D DDA in analyzing wedge stability.Firstly,the important factor─wedge safety factor F_sis obtained,which can judge whether the wedge slides or not.Then,by adjusting the geometric and physical parameters that affect the wedge safety factor,the results of 3D DDA numerical simulation are compared with the analytical solutions by using the control variable method.The reliability of the 3D DDA method in slope wedge stability analysis is verified,and the shortcomings of 3D DDA in judging wedge stability in critical state are pointed out.The limitation of the original 3D DDA to judge the statuses of each contact vertex of joint contact under critical conditions of rock wedge is analyzed,and a critical sliding contact criterion based on the sum of the contact forces at each contact vertex of the same joint is proposed to determine the whole joint contact state.Under the condition of critical friction angle and near critical friction angle,comparing the original and improved 3D DDA for single-block and double-block wedge model stability calculation results,it is verified that the improved 3D DDA is in good agreement with the analytical solutions of wedge stability under critical stability states.The improved 3D DDA has high accuracy in calculating the stability and movement process of wedge after failure.Based on the improved 3D DDA method,a 3D numerical model of a rock slope engineering in Tibet Autonomous Region is established,and the instability failure and movement characteristics of wedge are studied.3D DDA numerical simulation shows that the wedge moves downward along the discontinuous structural planes on both sides.Influenced by the occurrence of structural planes,its own shape and slope topography,the wedge continuously shifts and rotates laterally,showing spatial kinematic characteristics.The wedge movement produces huge kinetic energy,which directly impacts and collides with the road surface,and constitutes the geological disaster of G318 National Highway.The basic relationships between the wedge failure and the number of sub-blocks of dangerous rock masses are studied by discussing the process of wedge failure and its movement and disaster caused by secondary structural plane.The secondary structural planes of wedge-shaped dangerous rock masses may be further developed and intersect with the main control structural planes,and the large wedge is cut into dangerous rock masses with three different cases of sub-blocks.Through 3D DDA numerical simulation,the instability and movement characteristics of wedge-shaped dangerous rock masses under different working conditions are analyzed,and the disaster prediction and evaluation of wedge-shaped dangerous rock masses under complex 3D terrain conditions are realized.