Research On Stability Of Stope Structure With Complicated Exploitations Of Multi-layer Gently Inclined Thin To Mid-thick Deposit

Multi-layer gently inclined thin to mid-thick deposits are unsually exploited layer by layer,the safety,efficiency and economy of exploitation of them are severely constrained,the multi-layer strip mining method can effectively improve the mining efficiency.The compressive failure and strength characteristics of layered rock pillar since it's the main supported medium of gently inclined goaf roof,and stress characteristics of various stope structures in the complicated exploitations are the key science problems of the stability judgment of stope structures in multi-layer strip mining processes.Based on the research methods of rock mechanics test,theoretical analysis,numerical simulation test and physical similar simulation test,the stability of the complex stope structures during complicated exploitations is systematically studied.(1)The multi-layer strip mining with subsequent backfilling method and strip cut and fill mining method were designed according to the special occurrence characteristics like "multi-layer" and "mid-thick" of multi-layer gently inclined thin to mid-thick deposit,respectively.The mining method evaluation model based on interval number multi-mentality ranking is designed,which could rank the interval number data in mining engineering of different risk preference conditions.The model was applied in the mining method evaluation of a typical multi-layer gently inclined thin to mid-thick deposit,and the multi-layer strip mining with subsequent backfilling method was determined as the optimal mining method.(2)On the basis of the uniaxial and triaxial compression tests,the influences of different bedding angles on compressive failure modes and uniaxial compressive strength of layered rock,and the compressive failure modes of gently inclined layered rock with different bedding strength were analyzed.Based on the PFC numerical simulation,the meso-crack development and particle displacement characteristics of gently inclined layered rock with different bedding strength of different failure modes,like polyline "oblique steps" failure,single and X-shaped shear failure,were revealed from the meso-level.Based on the Mohr-Coulomb criterion and the fracture mechanics theory,the breaking angle formulas of the intact rock between beddings in the polyline "oblique steps" breaking surface was deduced,and the compressive strength criterion of gently inclined layered rock were also established.(3)The evolution law of stress transfer in multi-layer strip mining of gently inclined deposit was analyzed based on the effective region theory,the stress distribution characteristics of one side and two sides uncontacted rock pillars were researched based on numerical simulation,the formula the of distressed zone height of gently inclined goaf roof was deduced based on the energy balance principle,the elastic mechanical models of one side and two sides uncontacted filling pillars and complex rock beam roof after complicated exploitations were established,and the distribution stress in them were calculated.The loaded characteristics of the stope structures during complicated exploitations of multi-layer strip mining were revealed through the above research about the pillars and goaf roofs.(4)Based on numerical simulation and physical similar simulation test,the dynamic processes of multi-layer strip mining were simulated,the stress and displacement fields of goaf roof,rock pillar,filling pillar and overlying rocks in the multi-layer sripe mining processes were systematically analyzed,the conversion processes of non-continuous small pressure relief zones to continuous large one during the two-step mining process of multi-layer strip mining were revealed.The research results were consistent with them obtianed by theoretical method,which further confirmed the load characteristics of stope structures during complicated exploitations by theoretical method.The research results show that the multi-layer strip mining technology for multi-layer gently inclined thin to mid-thick deposit and the application effect evaluation model were developed,the compressive strength criterion of gently inclined layered rock and the compressive failure criterion of it with "oblique steps" type failure mode were established,the stress evolution of surrounding rock and load characteristics of different stope structures during the multi-layer strip mining process were revealed.At last,the stope structure stability judgement criterion of it during complicated exploitations was formed based on the compressive failure criterion of gently inclined layered rock pillar and the load characteristics of different stope structures,which provides the theoretical basis of stability analysis and design basis for multi-layer ore co-mining of multi-layer gently inclined thin to mid-thick deposit.