Investigation On Joint Parameter And Failure Mechanism Of Surrounding Rock Masses In Goafs

Goaf stability is an important factor restricting the safety production of mines,especially for the complex overlapped goafs,where the goafs are interrelated and influenced with each other,and the stress regime is extremely complicated.Local rock mass failure can easily lead to large-scale chain collapse and destruction,resulting in significant property damage and safety accidents,with very high level of danger.It is difficult for a single engineering evaluation method or research method to fully reflect the stability,destruction process and mutual restraint relationship of the worked-out areas.And it often fails to obtain the internal process of micro-cracks and the mechanism of chain collapse in surrounding rocks.Focusing on the issue of the stability of surrounding rock and continuous collapse of road way,this paper combined with the software system development,engineering experience improvement,numerical simulation,micro seismic monitoring and moment tensor inversion methods,and studied the stability and chain collapse mechanism of the overlapped goafs from different aspects and angles.The main work and achievements in this thesis are presented as follows:1.The evaluation system for rock mass stability and the automatic identification system for rock masses structural plane were developed.Those systems include rock mechanics parameter calculation module,BQ classification module,RMR classification module,improved Mathews stability graph method module,automatic processing module for structural plane data,three-dimensional crack network reconstruction module,RQDt module and permeability tensor K and damage variable D module.The systems can automaticly calculate the mechanical properties of rock mass.2.The investigation of the size effect and RQDt of rock mass were performed,to obtain the size effect of rock mass,RQDt space effect and the optimal threshold t.The calculation formula of RQDt under anisotropic condition was proposed.The Q of Barton rock mass was corrected and the influence of trace length on RQDt was studied.3.Based on the anisotropy of RQDt,the Barton rock mass(Q)and Mathews stability graph method were improved.The processing program for improved Mathews stability graph was developed.The improved Mathews stability graph method was applied to engineering application to research the surrounding rock stability of Hongling lead-zinc mine.Numerical simulation method was used to acquire the failure modes of roofs and surrounding rocks in the recovery of Ore body in Hongling lead-zinc mine.A research method for the stability of overlapped goafs was proposed based on the improved Mathews stability graph method and numerical simulation.4.Based on micro seismic monitoring technology and moment tensor theory,the crack source information of rock mass was inversed and identified,and the fracture shape and space-time evolution of cracks were determined.Combined with the on-site mining activities and micro seismic event curves and energy curves,the specific causes of the surrounding rock collapse were explored and the event threshold and energy threshold were determined.The dynamic failure mechanism of surrounding rocks in pillar recovery was investigated by numerical simulation.Through combining the abrove methods,the crack evolution mechanism of roadway chain destruction was determined.5.Two kinds of middle pillars overall mining technology programs were proposed,and the best recovery program was determined from the aspects of stress evolution and influence sphere.