Quantitative Discrimination Of Karst Development Degree And Risk Assessment Of Water Inrush In Limestone Of Coal Seam Floor

Coal mine water inrush disaster is one of the important disasters faced by coal mining in China.In order to study the difference of karst development degree of limestone aquifer in No.13 Coal Mine of Pingdingshan Coalfield and the risk of water inrush from Carboniferous limestone and Cambrian limestone aquifer in coal seam mining,the development degree of Carboniferous limestone and Cambrian limestone karst in No.13ore was quantified by using multi-dimensional extension matter-element model.Based on this,the karst development degree,unit water inflow,water inrush coefficient,fault complexity and mining depth are used as evaluation indexes.The evaluation model of water inrush from coal seam floor is based on improved AHP and Fuzzy variable set theory.The following research results have been achieved:?1?The karst aquifers of coal seam floor in No.13 Coal Mine are mainly Carboniferous and Cambrian limestone.The Carboniferous limestone L₂ and L_5-7 are water-rich aquifer,which constitute the aquifer of direct water-filling of coal seam floor.The Cambrian limestone is of great thickness and pressure,which is the indirect water-filling source and threatens the mining work of coal seam floor.?2?The degree of karst development differs zonally.The karst development degree of Ji-1 and Ji-2 mining areas is II-IV grade,for an average quantification value of 3.0,Ji-3mining area is III-V grade,for an average quantitative value is 4.0,Ji-4 mining area is IV-V grade and for an average quantitative value is 4.7,i.e.Ji-4 mining area has the highest karst development degree and Ji-1 and Ji-2 mining area is the lowest.In the vertical direction,the development degree of L₁-L₄ in Carboniferous Taiyuan Formation is grade IV-V,for an average quantitative value is 4.5,the L5-L7 in Taiyuan Formation is grade III-V,for an average quantitative value is 3.75,the Cambrian limestone is grade II-IV,for an average quantitative value is 2.75;that is,the development degree of karst gradually decreases from shallow to deep.?3?The fractal dimension of fault structure in No.13 Mine was determined based on the fractal theory.The results showed that the complexity of fault structure in mining area was divided into five classes according to the fractal dimension.The fractal dimension is less than 1.3,accounting for 34.04%,the fractal dimension was between 1.3 and 1.5,accounting for 23.4%and the fractal dimension is more than 1.5,accounting for 42.56%.The average fractal dimension is 1.36,and the fault complexity is medium.?4?Coupling improved AHP and Fuzzy variable theory to evaluate the water inrush danger of the No.13 Mine coal seam floor.The evaluation results showed that the water inrush danger of the No.13 Mine is also divided into five grades according to the evaluation results.The evaluation results of Ji-1 and Ji-2 mining areas were less than 3.0,which were divided into non-water inrush dangerous zone.The mining area has been excavated,no water inrush accident has occurred,and it is consistent with the actual situation.The evaluation results of Ji-3 mining area was between 3.5 to 4.5,which can be divided into high dangerous zone;the evaluation results of Ji-4 mining area was between2.5 to 3.5,which can be divided into medium dangerous zone.