Subsidence prediction by the use of influence functions

Abstract

Abstract Surface subsidence occurs as a result of extraction of a mineral resource at some depth below the surface. Most coal is mined in this way in the United Kingdom and such coal workings are responsible for the great majority of subsidence and associated damage that occurs. Hence it has become necessary to develop methods of predicting the amount of subsidence likely to develop due to coal mining. Many methods have been advanced, dating back to the latter part of the last century. However, they can be separated into three groups, namely, the theoretical, the empirical and the semi-empirical methods. A number of these methods were reviewed with the object of selecting one which lent itself to the development of a relatively simple computer program that could be used on a microcomputer. The complementary influence function method was chosen and, although by no means a perfect method, a program was developed to predict a complete subsidence profile for a given set of circumstances. The concept of complementary influence functions considers not only the influence of the extracted elements on a surface point but also the influence of the material remaining after extraction. The subsidence of a surface point then is found by integrating the response of every element in the area of influence, whether mined or not. The mined region is divided into a number of mined and unmined elements. Summing the influence of all the elements on a particular point yields a picture of subsidence at that point. If this is done for a number of points across the proposed extraction area, then a complete picture of the subsidence over the area can be obtained.