Study On The "Up And Down Fractures" Model Of Overlying Strata Mining Under High Pressure And Thick Loose Layer And Its Application

Lianghuai mining area is widely distributed with high pressure and water rich thick loose layer.Under this condition,the original fissures in the bedrock weathering zone under the loose layer are abnormally developed,which is easy to form"downward fissures" connecting the overlying loose aquifer and the lower bedrock.At the same time,the coal seam mining under the action of high water pressure is very easy to damage the original roof rock structure,so that the original roof rock fracture occurs,thus forming the bottom-up through cracks,called "upward cracks".Under the condition of“up and down fractures”fully developed,the fracture zone is easy to connect with the upper loose aquifer,resulting in the occurrence of roof water disaster.Therefore,the research on the formation mechanism and development characteristics of "double row fractures" provides a good theoretical basis for the safe mining and improving the economic benefits of Lianghuai coalfield in the future,and has a good application prospect.The main achievements are as follows(1)Based on the analysis of hydrogeological characteristics of loose layer in Lianghuai mining area,this paper focuses on the characteristics of aquiclude in Qidong Coal Mine.Based on the analysis of water inrush accidents of loose strata in Qidong Coal Mine,the general conditions of water inrush in loose strata of overlying strata of coal seam roof in Lianghuai mining area are summarized.(2)Through theoretical analysis,the development mechanism of "upward fissure"is obtained,and its abnormal development is analyzed.Combined with the geological conditions of 7131 working face in Qidong Coal Mine,FLAC3D software is used to simulate the development height of“upward fissure”under different water pressure.Results from 39.58m to 59.88m under 5MPa water pressure.With the increase of water pressure,the fracture production ratio increases from 13 to 19.Through simple hydrological observation and color borehole television method to test the development height of“upward fissure”in Qidong Coal Mine,the split mining ratio of medium hard overburden in fully mechanized mining of 71 coal mine and 32 coal mine reaches 20.7?34.1 and 15.3?28.1 respectively,which is much larger than that of other coal mines.(3)Through theoretical analysis,the development mechanism of "downward crack" is obtained,and the mining situation of 1121(3)working face in Dingji Coal Mine is simulated by numerical simulation method.The existence of“downward crack" is confirmed by analyzing the changes of internal stress field and plastic failure area in the weathering zone under the loose layer.Through the fracture permeability test under high water pressure,it is concluded that the permeability coefficient of weathered fine sandstone increases the most.The formation path depth of "infiltration zone" has a positive proportional relationship with the water pressure of water pressure borehole.Through logging,it is proved that there is water content in the primary fracture of bedrock weathering zone,and the field measurement results show that there is a positive proportional relationship between the formation path depth of "infiltration zone" and the water pressure value of water pressure borehole.(4)Based on the theoretical derivation of the development height of "up and down fractures",a“up and down fractures”model is proposed.In the water inrush risk assessment of 7114,7122,3222 and 7130 working faces in Qidong Coal Mine,only one working face's judgment result is consistent with the actual situation,while the judgment result of "double row fracture" model is consistent with the actual situation.It shows that the model has a certain reference significance in the actual mine production.Figure[36]table[10]reference[101]...