A New Method of Point Pillar Grouting for Old Longwall Goaf

Old goaf grouting filling technology and methods for controlling the residual subsidence were studied based on analysis of the activation mechanism of old longwall goaf and part mining strata movement control theory. The results show that grouting filling for the old longwall goaf can be divided into the point pillar grouting, the strip grouting and the whole grouting three types. A new designed method of point pillar grouting for old longwall goaf was proposed. Furthermore, column size and hole spacing design principles of the point pillar grouting were proposed through the theoretical research. In order to grout and fill for boundary hollow and under-voltage dense area of the mined-out area, grouting hole should first be arranged in mined-out area (within the scope of diffusion radius of grouting body) near the border.