Coordinated waterproof mining mode under thick loose sand stratum in Barapukuria coal mine

The geological mining conditions of Barapukuria coal mine are characterized by “ three thick” features of strata structure,namely the aquifer with thick unconsolidated formation near the surface,the special thick coal seam and thick roof. There are many aquifer groups in the overburden strata above coal seams. Water hazard in the coal mine is the main factor that threatens safe mining. Under the condition of overburden and multi-water body,in order to pre-vent the water in the loose UDT aquifer near the surface entering the underground longwall face,and avoid the water outburst disaster in the mine,the prevention and control mode of mining water hazard is put forward to protect the up-per aquifer and drain the lower aquifer. The key technology of one-layer safe mining is to control the structural stability of compound key stratum. The initial post-buckling theory is used to analyze the stability of compound key stratum,and the ultimate failure length of key stratum is obtained. Under stratified mining condition,the formulas for predicting the development height of water conducted fracture zone in overlying strata are given by linear regression,and the width of working face in stratified mining is not more than 150 m and the mining height is limited to 3 m. According to the safe height of coal pillar to protect UDT aquifer,the mining height of second-layer mining is determined. After second-layer mining,the key stratum of overburden structure is destroyed,which can not only effectively drain the aquifer water be-low the LDT aquiclude,but also ensure the integrity of the LDT aquiclude,and it can achieve the purpose of UDT wa-ter body with no leaking,which ensures the safe mining of the coal mine. According to the principle of coordinated and damage reduction mining in working face,it is determined that the reasonable offset of mining layers is about 82 m. Layout pattern of stratified thick coal seam and limited mining height with rational offset is put up. The roadway of low-er seam is located under the upper goaf,which can reduce the superposition of overburden stress and the deformation and damage of LDT aquiclude. The mining results show that the method of layered coordinated mining in thick seam can effectively reduce the stress superposition damage of LDT aquiclude under UDT aquifer and protect the integrity of aquiclude. In one-layer limited-height fully mechanized mining and two-layer limited-height fully mechanized caving mining,two aquifer groups from coal seam roof to LDT floor are separately drained,which solves the problem of water hazard prevention and control under the condition of small drainage capacity of mine. The staggered coordinated layout mining method of stratified working face effectively reduces the development height of water conducted fracture zone at mining boundary,reduces the degree of LDT deformation and damage,releases the stress of coal pillar in a stratified section,and realizes the overall subsidence of overburden. It not only effectively reduces the height of overburden fail-ure,but also reduces the impact strength of rock burst. During the mining,UDT water level changes within a certain range,which realizes the safe mining mode of thick seam with upper and lower sparse seams under the condition of multi-water body.