Slow stress waves recorded in extensometer data in a mine shaft, Queensland

Abstract

Five years of semi-continuous displacement records from extensometers installed though a concrete mine shaft lining are analysed and interpreted. The data includes multiple episodes of contraction which have amplitudes up to 15 mm in individual extensometers. Detailed analysis of extensometer data suggests transient high stresses occur in the shaft lining. The amplitude, wavelength and frequency of the observed transient stresses gives a unique insight into the progressive redistribution of stress around underground infrastructure during mining. The displacement pattern can be modelled as comprising a circular, elliptiical and translational component. The elliptical flattening direction indicates a consistent north-south compression in most events analysed. The typical duration of the wave events is approximately 5 h indicating a slow creep-like mechanism. Although some events appear to occur on a 24 h cycle, comparison with the mining activity record did not show a close association with the stope excavation sequence.