Influence of faulting on a mine shaft - a case study: part II - Numerical modelling

The X41 shaft is the man and supply shaft at Copper Mine, Mount Isa, Australia. There has been observed evidence of degradation manifested by the development of cracks in the shaft concrete lining since the early nineties. In addition, the shaft steel structure is being deformed and needs regular and meticulous maintenance. The shaft degradation has been attributed to the presence of two major geological structures, the W41 and W42 faults, which intersect the shaft in two distinct locations. Since the X41 shaft gives a direct access to the Copper Mine, it has to remain operational for the mine life. An objective of this study was to gain a better understanding of the mechanisms inducing damage to the shaft. In order to assess the long-term integrity of the shaft, it was essential to evaluate the impact of its deformation, related to the late mining status of the Copper Mine and the presence of the two major faults. It was important to determine an estimate of the future rate of displacement, as well as the total displacement, for the rest of the mine life. This paper presents a case study whereby the causes of shaft degradation were examined. The influence of faulting and mining sequence on the stability of the main mine shaft were investigated by means of field investigations and numerical modelling. This paper concentrates on the numerical modelling performed as part II of this project. It presents exhaustively the methodology used to build the numerical model and presents the outcomes. (C) 2002 Elsevier Science Ltd. All rights reserved.