Study of mining the safety pillar against sand by caving method under conditions of thick ravelly ground and super thin capping rock

In order to mine the safety pillar against sand under the conditions of the thick ravelly ground and the superthin capping rock, we put into an effect idea of breaking the fourth aquifer and protecting the third aquifer of the Quaternary system on the basis of the hydrogeologic conditions of the third aquifuge and the fourth aquifer by means of mine dewatering from the fourth aquifer, reasonably determining the ratio of the caving height and the mining height and preventing the shearing break in the capping rock over the working face to control the roof stability effectively.The coal more than 4×10⁵ t have been mined successfully since the study of the question, the profit of which is about 40 million Yuan.