Zone feature and control technology of overlying strata mining-induced fracture in shallow buried compound goaf

WANG Beifang; LYU Yuanhao; ZHANG Jing

doi:10.12438/cst.2024-0715

Abstract：The overlying strata fracture caused by shallow and close coal seam mining is developed,and air leakage condition is complic-ated,which leads to prominent hidden danger of residual coal spontaneous combustion and seriously restricts the safe and efficient produc-tion of Lijiahao coal mine.Therefore,similar experiment and numerical simulation were used to delimit mining-induced fracture zone in overlying strata of shallow buried compound goaf,fractal geometry theory was utilized for quantifying the fracture in zone of overlying strata.Based on the key layer theory,the cause of the overlying strata fracture zone was revealed and targeted control technology plan was proposed.The results showed that,the overlying strata fracture circularly opened and closed during 31114 working face mining,while the surface periodically produced dip dynamic crack behind the working face.Ultimately,the fracture distribution in overlying strata of shal-low buried compound goaf presented"M shaped",which could be divided into irregular fracture zoneⅠin caving zone,oblique breaking fracture zone Ⅱ,Ⅲand oblique separation fracture zone Ⅳin fracture zone and the edge crack was formed inside the goaf boundary.Among them,the void of fracture zone Ⅰintricately developed and disorderedly distributed,so the fractal dimension of the fracture net-work was the largest,1.569.Then followed by fracture zone Ⅱ,ⅢandⅣ,1.531,1.396 and 1.438 respectively.The mechanical model and instability criterion about"voussoir beam"structure of broken key rock block in overlying strata of shallow buried compound goaf were built to explain that the rotation deformation and instability of the"voussoir beam"structure of key layer in main roof led to the ob-lique breaking fracture opening in fracture zone ⅡandⅢ,while the combination bearing effect of the"voussoir beam"structure of key layers in main roof and interlayer resulted in oblique separation fracture development in fracture zoneⅣ.The surface-underground collab-oration control technology of overlying strata oblique fracture and surface crack in shallow buried compound goaf was put forward.That was the advancing speed of the working face was increased to 14 m/d at the stage of entering and leaving the overlying goaf and final min-ing,combined with backfilling wind-deposited sand and covering loess to deal with surface crack of fracture zoneⅡ,ⅢandⅣ.SF6 tracer technique test proved that the surface air leakage was small and the control effect of overlying strata mining-induced fracture in shallow buried compound goaf was good,which provided an important theoretical basis for the prevention and control of residual coal spontan-eous combustion.