Study On Fracture Development Characteristic And Prevention Mechanism Of Runoff Flood Induced By Thick Seam Mining Under Valleys

Many thick coal seams with shallower buried occurred in some major coal producing areas such as Shanxi,Shaanxi,Inner Mongolia and Xinjiang,and gullies grow widely on the earth’s surface.What is more,the seasonal runoff time is concentrated,with larger water volume and fiercer water potential.Therefore,the mining fractures in shallow and thick coal seams under special topography is easier to connect with the surface runoff,and the potential safety hazards on underground production caused by it can not be ignored.Based on the engineering background of thick coal seam mining in gully-growth-wide mining area,the breakthrough points of hazard and prevention of the seasonal runoff in valley,and the basic countermeasures with intervention between fractures and runoff for water hazard prevention and control,a systematic study was carried out combined with the activity characteristics of overburden and the development characteristics of mining fractures under different types of slopes during thick coal seams mining.And field investigation,physical simulation experiment of similar materials,numerical simulation experiment and theoretical analysis were used as the research methods in this paper.The main achievements can be summarized as follows:(1)The basic characteristics of coal(rock)bed occurrence,gully growth,and surface runoff in research area were mastered.The typical shape(The angle and height are concentrated in 20~50° and 40~100 m,respectively.)of gully mining slope which has great influence on mining and has a wide distribution range was defined.Based on the controlling effect of key strata on the rock strata at the bottom of slope body,the rock strata of slope body were divided into erosion loss of main(sub)key strata and complete sequence according to the spatial structure.Additionally,The seasonal characteristics of gully runoff and the basic mode of it causing flood were expounded.(2)The characteristics of overburden activity and mining fractures growth of different types of gully slope body occurrence structure were mastered.When the gully slope was located in the fractures zone,the slope rock strata show the characteristics of sliding and overturning towards the bottom of the gully,and the sliding and overturning of the slope rock strata were more obvious when the key strata were eroded.The shape and distribution characteristics of the connect between the mining fractures and the gullies were clearly defined,in which horizontal sliding cracks were dominant accompanied with longitudinal tension-shear fractures in the foot area of the slope when mining direct to gullies,while tension-cracks were dominant when mining back to gullies,besides,the cracks were mainly concentrated in the middle and upper part of the slope.(3)The concept of spatial linkage influence height of key stratum breakage was put forward,and the prediction model of overburden mining ractures development height is constructed.It was clearly defined that the precondition of water hazard caused by gully runoff shaped with mining under slope body was that the rock stratum at the bottom of gullies was located in the fracture zone.Additionally,the sliding mechanics model of rock stratum at the foot of slope was established,which revealed the mechanism of sliding failure and horizontal sliding cracks of rock stratum under slope body.This paper expounded the spatial position relationship between working face and slope body with gullies when water hazard of gully runoff caused by the connection of mining fractures and gullies occurred,and the determine method of the safe distance between mining fractures and gullies was also put forward.(4)The influence of slope angle,slope height,mining thickness and the depth of coal seam at the bottom of the gully on water hazard of gully runoff was researched,and the influence characteristics of slope angle,slope height and minimum mining ratio at the bottom of the gullies on safety distance of working face under slope were revealed.Based on the safe coal pillar generalized model of gully runoff,the size of safe coal pillar and its determination method were put forward according to the safe distance of working face.Combining with the causing conditions of gully runoff water hazard,the prediction system of gully runoff water hazard threat under slope mining and the technical measures of prevention and control in well and underground were also put forward,which enriched and improved the connotation of safety and efficiently mining of thick coal seam in gully-growth-wide mining area.There are 130 figures,24 tables and 132 references in this paper.