| Dongsheng Coalfield is an important raw coal producing area in China.Large scale coal mining will cause a large number of cracks in the overburden,bring hidden dangers to the working face and destroy the fragile ecological environment.Therefore,it is necessary to study the development law of water flowing cracks.In this thesis,theoretical analysis,field measurement,numerical simulation and other research methods are comprehensively used.Through the investigation and analysis of the occurrence of 22 coal seams,the 3-1 coal seam in Dongsheng Coalfield is divided into four typical zones.The development law and fluctuation difference of water flowing fractures in different zones are studied,and the determination method of water flowing fracture zone in different zones is obtained.It provides a basis for the green and safe development of coal resources in different zones of Dongsheng Coalfield.According to the different burial depth(H)and mining height of 3-1 coal seam,Dongsheng coalfield is divided into four typical zones: zone I,zone II and zone III are located in the east of the north-south axis,and are distributed from north to south along the boundary between Shaanxi and Inner Mongolia,and zone IV is located in the west of the axis.In zone I,H ≤200m and the mining thickness is 2-5m with an average of 4.4m;In zone II,200m<H ≤500m and the mining thickness is 3-6m with an average of 4m;In zone III,500m<H ≤800m and the mining thickness is 4-6m with an average of 5m;zone IV,which has not been developed yet.Through zoning,it provides a basis for mastering the characteristics and differences of the development of water flowing fractures in different regions.Based on the field measurement and a large number of statistics of the height of water flowing fractured zone in four typical zones,it is found that the mining fracture mining ratio in zone I is 10.9-35.5,with an average of 21 and a dispersion coefficient of 0.39;the mining fracture mining ratio in zone II is 17.5-48.7,with an average of 30 and a dispersion coefficient of 0.44;the mining fracture mining ratio in Zone III is17.21-24.6,with an average of 21.3 and a dispersion coefficient of 0.12,which shows the discrete degree of fracture mining ratio in zone I and zone II is obviously larger than that in zone III.Based on the theory of key strata,the development mechanism of water flowing fractured zone in zone I,zone II and zone III is analyzed.It is found that the low position of main key strata is the reason for the large fluctuation of mining fracture mining ratio in zone I and zone II,and the small spacing of adjacent key strata near 7-10 times of mining height above the coal seam roof is the reason for the small fluctuation of mining fracture mining ratio in zone III.Therefore,according to the geological column,the height of water flowing fractured zone must be determined by using the height prediction method of water flowing fractured zone based on the location of key stratum;the height of water flowing fractured zone in zone III can be determined by 20-25 times of mining height;the deep undeveloped zone IV can be predicted by referring to the method of zone III.There are 38 figures,9 tables and 116 references in this thesis. |
