Fracture Field Evolution And Seepage Law Of Overlying Strata Induced By Shallow Buried Coal Seam Group Mining

The development of overburden fracture network in shallow buried coal seam group(SBCSG)mining frequently triggers water disaster accidents.The evolution of overburden fracture field and seepage law are the basic problems of goaf water prevention and control during re-mining,which directly affect the evaluation of water disaster and the formulation of prevention and control technical scheme.Theoretical analysis,numerical simulation,laboratory experiment and field measurement were adopted,the different types and timing of fracture development and conduction of overburden strata in SBCSG are obtained,and the nonlinear attenuation law of compaction permeability of fractured rock mass in composite goaf is revealed.The stress-void-seepage coupling model of goaf is constructed,and the permeability evolution characteristics of overburden strata are analyzed.The technical scheme of reducing permeability and eliminating water inrush in SBCSG mining is put forward.The research results provide theoretical support for goaf water prevention and water-preserved mining in SBCSG.The main innovations are as follows:(1)The key factors affecting the fracture evolution of re-mining overlying strata were analyzed.A Python-based numerical algorithm and program for rapid cross-scale calibration of rock reasonable compressive-tensile strength ratio are developed.Image recognition technology is introduced to evaluate the stability of irregular room goaf.The influence of overburden structure,mining height and interlayer spacing on the fracture evolution law of re-mining overlying strata is studied by numerical simulation,and the type and timing of re-mining fracture conduction are obtained.The calculation model of equivalent mining quantity of overburden rock is established,and the subsidence curve equation of overburden rock in composite goaf is fitted in sections.The void retention of re-mining under two kinds of goafs,which are insufficient caving goaf and full caving goaf,is calculated.The self-similar characteristics of void retention ratio in vertical adjacent areas of mining overburden rock are found.(2)The characteristics of fractured coal-rock combination in composite goaf are determined by investigation,and the stress path model of gravel in overlying goaf is established.The effects of lithology,particle size,combination characteristics,mining intensity and caving re-compaction on the compaction and seepage characteristics of the composite goaf were tested.It was found that the graded mudstone compacted in the goaf had the most water-proof performance recovery potential.The evolution characteristics of the seepage field of the re-mining engineering environment of the SBCSG were analyzed,and the nonlinear attenuation mechanism of the compaction permeability of the goaf was revealed.(3)The order of magnitude of permeability predicted by the empirical formula and the fitting model is compared,and the stress-void-seepage coupling model considering compaction and re-breaking is established.The proposed permeability change process sensitivity and dynamic sensitivity index are used to evaluate the water-proof recovery ability,and the conditions for the sudden increase of permeability in re-mining are determined,and the grouting and permeability reduction technology of fractured rock mass is proposed.The self-similar characteristics of permeability attenuation of overburden rock in fractured zone are found,and the prediction model of caving zone height in composite goaf based on the concept of equivalent layered mining height is constructed.The numerical analysis methods of compaction permeability of fractured and broken rock mass are proposed respectively.(4)Aiming at the problem of goaf water prevention and control in Shaping Coal Mine,the delayed recharge characteristics of atmospheric precipitation and the catchment characteristics of goaf are analyzed by field measurement.The reliability of the predicted results of the height of the caving zone in the composite goaf is verified by the borehole measurement.The numerical analysis model for the permeability of the overlying strata is used to obtain the temporal and spatial evolution law of the permeability of the overlying strata.The technical schemes of grouting clogging and seepage reduction and comprehensive drilling drainage are proposed and tested,and the safe mining of SBCSG is realized.The dissertation contains 105 pictures,54 tables and 211 references.