Instability mechanism and design method of coal and rock pillar under water pressure

In terms of the problems of instability and sand inrush of coal and rock pillar in working face of wedge area under special geological conditions,such as thick loose aquifer,thin bedrock,and so on,taking the water inrush and sand inrush disaster from No. 11071 working face of Zhaogu No. 1 Coal Mine as an example,combined with geological drilling data,a geological model of wedge shape preserving water pressure mining-sand inrush is established. Through clay liquid plastic limit test,dried and saturated water absorption and disintegration test,it is concluded that bottom clay and weathered mudstone has a good water-proof performance,and can form a “wedge protect pressure” structure. On this basis,through the experiment of weathered mudstone mining crack extension under water pressure,the inherent disaster-causing mechanism of instability of coal and rock pillars of sand layer that is affected by mining damage under water pressure is studied. The results show that under a high water pressure,the mined crack in weathered mudstone extends to pipeline,thus the sand-proof properties of the protective layer fail. Considering the damage thickness of weathered zone of coal pillar,the method of setting up the sand-prevention safety coal and rock pillar under water pres- sure was put forward,and an engineering application was carried out in No. 11191 working face and achieved the ex- pected results. Research results complement the design method of sand prevention safety coal and rock pillars in China,and can reduce the coal mine collapse sand disasters and accidents.