Study of "3-Step Mining" Subsidence Control in Coal Mining Under Buildings

Mining subsidence damage is the main factor of restricting coal mining under buildings. To control or ease effectively the degree of mining subsidence and deformation is essential to resolve this problem. Through analyzing both advantages and disadvantages of some technologies such as mining with stowing, partial extraction and grouting in separated beds of overburden, we used the principle of load replacement and propose a "3-step mining" method, a new pattern of controlling mining subsidence, which consists of: strip mining, i.e. grouting to fill and consolidate the caving zone and retained strip pillar mining. The mechanism of controlling mining subsidence by using the "3-step mining" pattern is analyzed. The effect of the control is numerically simulated. The preliminary analysis shows that the "3-step mining" can effectively control ground subsidence and deformation. By using this method, the ground subsidence factor can be controlled to a value of about 0.25. Coal recovery can reach 80%-90%. Coal mining without removing surface buildings can be realized and the economic loss resulting from ground subsidence can be greatly reduced.