Study of mine stability using records of ground tilting

Abstract

Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the performance of dip pillar systems. The tilt data are being recorded by a triggered seismic recording system. The triggered data showed velocity and tilt data that correlated well in time, allowing for separation of the tilt data into coseismic and aseismic tilting. The following results have been obtained from analysis of data recorded over 109 days: Coseismic tilt jumps occur in either direction; the total amount of coseismic tilt in each direction is approximately the same; the time-of-day tilting shows the effect of blasting on the coseismic tilting and, to a lesser degree, on aseismic tilting. As a preliminary interpretation, this can be attributed to the brittle nature of the rock mass and to the “stiff” mining layouts practiced in the area. As a more definitive interpretation, this observation is compatible with a level of stress of the rock blasted at the face that is very much lower than would have occurred if the rock were infinitely strong and unfractured; and Tilt jumps show a power-law behaviour compatible with the Gutenberg-Richter relationship with b = 1 over more than two orders of magnitude. Numerical tools have been developed to estimate tilting from mining, assuming elastic rock mass behaviour. Some suggestions for further work are made. These include studying changes in a seismic tilting following tilt events associated with shrinking pillars. This might provide more direct insights into pillar stability than are obtained from the general results obtained here.