Research status and prospect on the mechanism of dynamic sand inrush at-weakly cemented strata in working face with thick bedrock

The superposition disaster of roof water and sand inrush and strong ground pressure in Huanglong and Ningdong coal bases in western mining areas of China is a dynamic sand inrush disaster of weakly cemented strata in working face with thick bedrock. This type of disaster is different from the water and sand inrush disasters in shallow and near loose layer working face in occurrence,material source and power source. It is a new type of roof disaster. Because this type of disaster is sudden,destructive and powerful,which poses a serious threat to safe production,how to effectively prevent and control the recurrence of disasters has become an urgent problem in many mining areas. At present,the understanding on the internal mechanism of disaster formation and the studies on the scientific problems are the basis and key to establishing the technical system of disaster prevention and control. This paper analyzes the overburden structure,formation conditions,and related research status in the accident mining area,and obtains the response law of bearing pressure and basic top load distribution under a hard rock to the deterioration of weakly cemented formation. Two key scientific problems,such as the dynamic formation mechanism and channel evolution law of degraded weakly cemented formation under the breaking action of hard rock,are the bottleneck to reveal the formation mechanism of disaster. Therefore,the research on the formation mechanism of disasters has formed three main research areas including the feedback characteristics and response relationship of the deterioration of weakly cemented strata when encountering water to the influencing factors,the variation law of the stress conditions of upper hard rock,and basic roof with the deterioration of weakly cemented strata,and the collapse dynamic mechanism of degraded weakly cemented strata and the channel evolution law under incremental load. The comprehensive active prevention,and control technical approaches of hard rock advanced splitting and weak cemented stratum grouting modification are put forward to fundamentally change the objective conditions of disasters. The research results will provide theoretical support for the development of a prevention and control technological system for the water and sand inrush of roof and concurrent disasters of strong ground pressure,and ensure the large scale safe development of Western coalfields in China.