A Simulation Study On The Wangxia Overhanging Rock Disaster In The Wu Gorge’s Channel Of The Yangtze River’s Three Gorges

The rapid development of the socio-economy has led to an increasing demand for mineral resources such as coal mines,which are highly susceptible to collapse and sliding disasters under mining activities,resulting in significant losses to the socio-economy.This has attracted widespread attention from scholars both domestically and internationally.Especially in the Three Gorges reservoir area in China,the tectonic movement is intense,and the Yangtze River undercuts erosion significantly.There are a large number of cliffs and slopes with lithology combinations of " hard upper and soft lower " in the reservoir area.To deeply explore the mechanism of creep,collapse,and slide of the slope in these unique geological conditions under mining action,and study the characteristics of its rockfall trajectory,this study focuses on the Wangxia Overhanging Rock in the Wu Gorge’s Channel of the Yangtze River’s Three Gorges,Conducted a systematic and complete simulation study.The main research contents and conclusions are as follows:(1)Based on field investigations,measurements,and engineering surveys,this study analyzes the terrain,lithology,geological structure,and hydrogeological conditions of the study area where the Wangxia Overhanging Rock is located.In particular,this study focuses on analyzing the historical deformation,damage,and movement characteristics of the Wangxia overhanging Rock based on displacement monitoring data and macroscopic deformation phenomena observed during field investigations.Further,this study identifies that the terrain of "steep upper and gentle lower" and joint cutting are the basic conditions,while coal mining and the creep of the soft rock at the base(lithological combination: hard upper and soft lower)are the main factors causing disasters;(2)Based on FLAC3 D,the mechanical response mechanism of Wangxia overhanging rock slope under the action of coal mining was studied.The simulation results were analyzed in detail from three aspects: stress,strain,plastic zone,and slope stability variation characteristics.The accuracy and reliability of the simulation results were verified through macroscopic deformation phenomena.The results showed that with the deepening of mining,the disturbance to the slope continued to increase,the area of the plastic zone is increasing,the stress concentration phenomenon at the slope toe and mining boundary is significant,and tensile stress appeared in the roof and local areas of the slope top,the displacement of the slope body continues to increase,and the stability continues to decrease,the stability coefficient has been reduced from initial2.94 to 1.18,indicating that the goaf of the coal seam greatly promotes the formation and destruction of the Wangxia overhanging rock;(3)Based on the Simulated Annealing Algorithm and BP Neural Network,an intelligent forward and inverse analysis method was constructed,which is used to inverse the creep parameters of soft rock at the base,and it is substituted into FLAC3 D forward analysis creep calculation.Numerically calculated displacement agrees well with the on-site measured displacement,the average relative error is 4.38%,verifying the accuracy of the inverse values of creep parameters.The simulation results show that as the creep duration increases,the maximum displacement and maximum shear strain increment values continue to increase,the displacement vector indicates that the overhanging rock mass exhibits a seat slide failure that is sheared out along the soft rock at the base,consistent with the actual deformation and failure characteristics.Based on field analysis,coal seam mining and creep simulation results,the evolution process of Wangxia overhanging rock collapse is summarized as following 4 stages:early formation and development of cliffs,bottom coal seam mining disturbance,creep deformation of base soft rock,and collapse disaster outbreak;(4)Based on the three-dimensional rockfall trajectory simulation software,the rockfall trajectory in the Wangxia overhanging rock area was studied,and the rationality of the parameter values was verified by comparing the trajectory simulation results with the on-site rockfall collapse and accumulation conditions.Based on this,a comparative analysis was conducted on the trajectory and motion characteristics of falling rocks with different initial velocities.The results showed that the larger the initial velocity of the rockfall,the longer the movement distance,the wider the trajectory distribution range,the higher the energy content,and the greater the danger.