Study On Overburden Failure Law And Rock Slope Stability In Downhill Mining Of Close Seam

China is the largest coal producer in the world,and coal plays an important role in China's energy production structure.With the rapid development of social economy,coal mining technology has reached a new height.At the same time,the safety and stability of coal mining in complex geological environment also meet new challenges.Coal mining is usually accompanied by periodic mine pressure appearance,roof fracture and other phenomena.The mining fracture field is usually the dominant channel for gas migration and groundwater seepage;the development of slope fracture through is usually one of the important reasons for inducing the huge landslide accident.In view of this,based on the national key research and development project(the formation mechanism of super large landslide under the underground mining environment in karst mountain area),taking Pusa coal field in Nayong County,Guizhou Province as the engineering background,this paper establishes a downward mining experimental model for the close seam,(1)through the similar simulation test,analyzes the failure characteristics of the mining overburden,and uses the discrete element software to analyze the mining overburden under different mining height conditions Based on the results of field investigation,the generalized mining model of deep and large parallel fractures developed along the slope toe and the top of the slope is established,and the influence of parallel spacing,vertical spacing and dip angle of fractures on the slope stability is studied.The main research results and conclusions are as follows:(1)Combined with the geological exploration data and field investigation,the paper analyzes the geological disaster situation of Nayong County,and carries out the basic physical and mechanical properties test of limestone.(2)In view of the similitude theory.the mold experiment of downward excavation of short distance coal seam is carried out.The results show that as the working face advances,the fracture angle gradually decreases,increases,decreases and tends to stabilize.and the separation fracture in the middle compaction area develops,expands and closes,and the mining fracture field generally presents the ladder shape distribution,which runs through to the slope toe surface.While this is accrod with the actual survey results,the excavation of the lower coal seam has a greater impact on the stress field of the upper coal seam floor;when the excavation is completed,the displacement of the slope overburden generally presents a symmetrical step distribution,and the slope parallel fracture rock bridge is affected by The influence of mining eventually penetrates and develops to the slope surface.(3)The results show that the stress peak value in the stress concentration area and the stress recovery level in the relief area are positively related to the mining height,and the displacement of the overburden increases with the mining height,but the maximum displacement influence height is higher than that of the key layer,and the fracture development is more full with the increase of mining height.At the same time,the fracture closure of the separated layer is also better More fully.(4)The results indicate the distribution characteristics of the deep and large parallel fractures have a great influence on the failure mode of the slope under the action of mining.When the fractures run through and develop,the slope body takes the upper fracture rock bridge lower fracture as the sliding surface,and when the lower fracture expands to the slope surface,the slope is partial Destruction.