Fuzzy probability measures (FPM) based non-symmetric membership function: Engineering examples of ground subsidence due to underground mining

Abstract

This paper introduces a new FPM method for prediction of surface subsidence due to inclined coal seam mining. Based on the non-symmetric membership function and the definition of the fuzzy probability measure, the mathematical model for the two-dimensional problem is developed and applied to the analysis of ground subsidence due to underground mining of inclined coal seam. The results of calculation with the new model indicate that the predicted value has good agreement with the measured data.

Introduction

Mining has an impact on the environment. Unfortunately, many former mining practices frequently have led to serious consequences. The impact of mining depends on many factors, in particular, the type of mining and the size of the operation. It can mean that land is disturbed, that the topography is changed and that the hydrogeological conditions are affected adversely. One of the most important impacts on the environment of mining is subsidence. Mine subsidence can be defined as movement of the ground surface as a result of readjustments of the overburden due to collapse or failure of underground mine workings. Surface subsidence features usually take the form of either sinkholes or troughs.

Increasing world demand for energy and mineral resources has resulted in much mechanization and rapid excavation techniques by modern mining operations (Anon, 1975). Exploitation of minerals using caving methods such as the longwall mining method will result in surface subsidence. This phenomenon can cause environmental problems and damage to surface and subsurface structures (Coulthard, 2001; Luo et al., 2002; Asadi, 2002, Asadi, 2003; Asadi et al., 2004). In order to protect the environment and structures from these damages, precise subsidence prediction is essential. When a horizontal seam is mined, the subsidence trough has symmetric shape, whereas in inclined seams it is non-symmetric and complicates the prediction of the surface subsidence profile (Whittaker and Reddish, 1989; Asadi et al., 2004).

In some countries, large volumes of coal reserves of high quality are classified as inclined and steep strata. For economic reasons, these deposits have to be extracted and, consequently, the problems of surface subsidence of these types of deposits are still highly relevant. During the last decades, several new models of subsidence prediction for level, inclined, and steep seams have been developed worldwide (Cui et al., 2000; Rodriguez and Torano, 2000; Toraño et al., 2000; Donnelly et al., 2001; Asadi et al., 2004). Still, there are some complexities in the prediction of subsidence profiles in inclined and steep seam mining.

In this paper, a new method for prediction of the ground subsidence due to inclined seam mining is developed. The fuzzy probability measures (FPM) and non-symmetric membership function were applied in deriving the method. A case study is used to demonstrate the improved prediction method. The non-symmetric membership function and the mathematical theory of fuzzy probability measures are used to solve the problems of rock mass mechanics due to underground mining. The use of the theoretical of fuzzy mathematics to the evaluation of movements and deformations and to describe the basic feature of the ground surface due to underground mining, is a new concept, especially for the mining of in inclined and steep seam.