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UBC Theses and Dissertations

Reviewing Laubscher’s empirical method to estimate subsidence limits Contreras, Constanza Patricia


A key characteristic of cave mining is the formation of a significant surface subsidence crater, which may impact nearby infrastructures, as well as have important environmental impacts. The most used empirical method in cave mining for estimating subsidence damage limits is the Laubscher method (2000). The original dataset at the core of the Laubscher chart does not reflect the conditions of the modern caves (i.e., deeper orebodies, stronger rock masses, and higher production rates). In addition, there is a need to review the definition of cave material factor. This research explains the limitations related to the method and evaluates new cases from recent cave mining operations for checking the validity of the empirical subsidence chart. In addition, the predicted cave angles could be used to calculate the volume of broken rock; however different factors could affect the proportion between the tons extracted and the growth of the crater, which are evaluated in this research using a case study. Among the limitations of this method are the MRMR, which has a lack of detailed guidelines to calculate its values; the unconfined area, related to the lower end of the “factor” and MRMR scale of the chart, which shows predicted cave angles too conservatives; the irregular topography with a greater difference in elevation, which is seen to result in lower cave angles over the peaks than the cave angles predicted using the method; the mining sequence and the structures, which are not considered in the method. The evaluation of new cases from recent cave mining operations showed that Laubscher’s method performs well in the prediction of cave angles; due to the average distance between the measured data values and the predicted data values is 4°. Moreover, the database shows a similar tendency that Laubscher’s chart because for a depth greater than 600 m the measured cave angles tend towards the same range of values (80°±4°) regardless of their geotechnical quality. Among the factors that affect the relationship between tons extracted by caving mine and estimated growth of the surface crater are the percentage of extraction, the topography, geotechnical quality, and mining sequence.

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