An underground iron mine in China has been used as a case-study to research the subsidence due to ore extraction and backfilling during open stoping operations. A 3-D discontinuum numerical model was built to scale incorporating geologic complexities including faults and interfaces between different lithologies, and the stoping and backfilling sequence adopted from the mine plans. The stoping was carried out in two vertically stacked horizontal layers, with a total of 16 stopes. Large displacements of up to 50 cm were observed along the roof of the stopes, and a maximum surface subsidence of 22.5 cm was observed at the surface. Backfilling was found to eliminate subsequent deformation and subsidence from occurring. The extraction of the upper orebody was found to influence deformations in the lower orebody. Finally, a subsidence profile was constructed to show the subsidence at all locations along the length of the surface and region of influence on the surface.
Surface subsidence is a significant problem affecting infrastructure, settlements and forests over underground workings. In this paper, a discussion on ore extraction, backfilling operations and the consequential surface subsidence is presented considering the case study of the Luohe mine in China. Luohe is an underground pyrite holding of the Magang Steel Company in the Anhui province of China. The 250 m thick orebody lies at a depth of 400 m (Magang, 2012a), under a significant number of surface infrastructure (Fig. 1) which need to be protected from any adverse consequences of mining the iron deposits. To limit the subsidence, the mine has adopted backfilling operations post extraction in all stopes. In this paper, a section of the unmined orebody is considered and analyses have been performed to predict the amount of subsidence that the region is likely to undergo due to the extraction methodology being currently adopted in the mine.
Because this study has attempted in incorporating the effect of in-situ stresses in the region, fault network, rock mass mechanical properties, interface features and backfilling operations on the subsidence, the discrete element method has been selected to carry out the analyses.