Study on failure characteristics of stope overlying rock considering strain hardening characteristics of caved rock mass

The overburden movement,deformation and damage of the overlying rock caused by coal mining directly affect the water storage and water supply capacity of the underground reservoir.In order to scientifically and accurately calculate the storage capacity of the underground reservoir,It is necessary to consider the influence of the mechanical properties of strain hardening in the progressive compaction process of the caving rock mass in the goaf on the height distribution characteristics of the two zones of the overlying rock in the stope.Taking Lijiahao Coal Mine as the engineering background,based on the mechanical properties of strain hardening in the compaction process of the caving rock mass,the double-yield model and the proposed inversion calculation method were used to study the failure characteristics of overlying rock in stope.The stress expression of the caving rock mass was deduced,and its influencing factors were analyzed.The numerical simulation calculation method was proposed,and the theoretical analysis and field measurement were adopted to reveal the influence of strain hardening characteristics of the caving rock mass on the development law of the two zones of overlying strata in stope.The research results show that:① The stress of the caved rock mass increases slowly with the strain increase; the stress exhibited an exponential growth when the strain reached a critical strain,and with the increase of the fragmentation coefficient,the critical strain also increases.②Based on the built-in double-yield model of FLAC3D,the inversion calculation method of cap pressure and material properties was proposed,and the simulation calculation of the strain hardening characteristics of the caving rock mass in the gob was realized.③The numerical modelling results indicate that when the compaction and support of the caving rock mass were considered,the movement range and degree of the roof strata were reduced; the height of caving zone was 15 m,a decrease of 16%.The height of fractured zone was 65 m ,which was reduced by 13.3%.Based on the field measurement results,the feasibility of the above simulation calculation method is verified.