Ground subsidence observations and a modified influence function method for complete subsidence prediction

The results of surface subsidence investigations carried out in different coal fields in India are presented in this paper. Important differences are seen to exist between the subsidence norms given in the Subsidence Engineers Handbook, UK and those obtained in Indian conditions. Differences also exist for extraction below unfractured or uncaved rock and below preexisting caved goaf(s). The subsidence is higher in the latter case and also in the slopes and strains. Consequently separate equations and guidelines have been given for these two conditions of mining. Since Indian coal mining is mostly under shallow to moderate cover, several cases of discontinuous subsidence have been observed. A demarcation limit for discontinuous subsidence is given, seeing that discontinuous subsidence causes severe surface damage. Since room and pillar mining is the principal underground method of extraction, panels of irregular shapes often occur making complete subsidence prediction difficult. The influence function method with a new function and additional functions for modelling subsidence asymmetry and the effect of extraction edges are given in this paper. The method for extraction below goaf(s) is also examined. Four cases are given for the comparison of observed and predicted subsidence contours and two cases for comparison of the slopes and strains. (C) 2000 Elsevier Science Ltd. All rights reserved.