Characterization and Empirical Analysis of Mining-Induced Subsidence over Block Caving Operations

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Erik Eberhardt, Andre Van As,
Abstract With the exhaustion of near surface ore deposits accessible through open pit mining, block cave mining methods (including sublevel and panel caving) are gaining increasing attention from the mining industry given their low cost relative to other underground mining methods. The method involves the undercutting, caving and bulk extraction of ore, which in turn leads to the development of surface subsidence above the propagating cave. Questions arise as to the extent and magnitudes of this subsidence as it may affect strain-sensitive infrastructure on surface.

Much of the work on the topic of mining-induced subsidence has been directed towards longwall coal mining and continuous subsidence, for which empirical procedures and guidelines are relatively well established. However, block cave mining produces discontinuous subsidence due to large movements around the cave controlled by geologic structures, rock mass heterogeneity, etc. Discontinuous subsidence is therefore not easy to predict due to rock mass complexity and uncertainty. Of further impediment is the sparse number of case histories available in which actual subsidence measurements are reported.

Given that such data is essential to better understanding discontinuous subsidence and its controls, this study reports the development of an exhaustive and comprehensive database of available (i.e. public domain) in-situ subsidence information from block cave mining operations from around the world. The objectives of the database are to lay the foundation for more effective numerical and empirical analysis of surface subsidence induced by block caving.

In summary, only 5% of the more than ninety mining operations populating the database report detailed subsidence measurement data. This includes both mines that have ceased to operate and those still producing. Those mines that do report measured surface subsidence profiles confirm that subsidence above block cave mines is largely asymmetric, meaning that the angle of break from the hangingwall and footwall differs. Other empirical relationships are likewise drawn to demonstrate the limitations of analysis techniques that do not explicitly incorporate geological structures and rock mass anisotropy. Lastly, guidelines will be provided that contribute to improving the accuracy of subsidence prediction based on correlations between different geological factors influencing subsidence and characteristics of the subsidence patterns measured.

Keywords: Block caving, Database, Characterization, Subsidence, Empirical analysis
Full Access to Technical Paper
PDF version for $20.00
Other papers from Rock Engineering 2009 - Rock Engineering in Difficult Conditions