Study On Strain And Geoelectric Response Characteristics And Test Of Deformation And Failure Of Surrounding Rock In Stope

During the coal seam excavation process,the overburden deformation and failure characteristics of the stope are an important parameter of mine safety production,which needs to be accurately detected by corresponding technical means and provide effective technical support for production.In this paper,numerical simulation is used to study the deformation and failure of overburden in mining stope.Based on differences in the physical properties of the overburden after failure of rock,the response characteristics of overburden strain field and geoelectric field in stope are analyzed,and propose the use of BOTDR and resistivity CT to conduct field monitoring.The dynamic test has significant effect and strong applicability.Based on the geological conditions of the 12309 working face of the Selian II Mine of Ordos basin in Inner Mongolia.The numerical model of 3-1 coal overburden deformation failure was constructed by FLAC^3D,and the mining failure characteristics were simulated according to the actual stoping progress of 3-1 coal.The simulation results demonstrate that the pressure relief area in the top and bottom floor of the excavation was arched,and with the increase of excavation distance,the radius and range of the arch are also increase.In the later period,due to roof caving and compaction of the mined-out area,the arched area of pressure relief area gradually disappeared.The stress state of overburden in mining area was a"saddle-shaped"distribution.The overburden strata of the stope mainly bear the shear failure,the height of the fractured zone is 59.2m,the displacement of overburden increases with excavation,and the maximum displacement is 0.083m.Based on the geological conditions of 3-1 coal and numerical simulation results,a overburden monitoring system was laid rationally.Using distributed optical fiber sensing measurement technology of Brillouin optical time-domain reflectometry（BOTDR）and borehole resistivity CT method comprehensively analyse and research strain field and geoelectric field.The results of the comprehensive test demonstrate that during the process of 3-1 coal mining,the deformation and failure of overburden occur preferentially in the strata with less elastic modulus and in the interface between soft and hard strata.The influence range of advance stress is 30m,and the top layer of coal seam 17.5m-34.5m is the key layer.The development height of the overburden caved zone is 17.5m and the height of the fractured zone is 54.5m.The average mining thickness of 3-1 coal seam is 2.5m,then thickness ratio between the caved and mining zone thicknesses is 7,the ratio between the fractured and mining zone thicknesses is21.8.Three kinds of technical methods(BOTDR,resistivity CT and FLAC^3D)were used to study the deformation and failure of overburden in 3-1 coal mining.The obtained technical parameters were basically the same within the error range.The mutual evidence of the three methods,compared with the previous single method,greatly improves the validity and accuracy of the test results,and provides certain technologies for prevention and control of mine water hazards,instability of roadway surrounding rocks and the retention of protective coal pillars support for mine safe and efficient production to provide protection.However,Limited by test conditions,relevant problems still need to be solved when using optical fiber and electric method for field testing.At the later stage,the research should pay more attention to such issues as the coupling of drilling and grouting,the design of drilling parameters,the selection of sensing unit and the quantitative explanation of data.