ARCHING EFFECTS AND SILLMAT BEHAVIOUR

CIM Vancouver 2002
Aldrich Philip Dirige,
Abstract The design of sillmats is normally based on experience and on trial and error methods, and various assumptions and rules of thumb are normally employed in design. Two of such rules of thumb are i) that arching effects will improve stability by reducing the fill pressure on the sillmat by some 30% of the value with no arching, and ii) that the sillmat should have a minimum thickness approximating the stope width. Use of such empirical based approach brings some uncertainty to design which may result in massive fill failure.

A study, based on centrifuge physical modelling, was developed for an operating hardrock mine to provide a comprehensive understanding of the effects of arching and sillmat thickness on stability. The assessment was based on scaled model stopes of different width (3 and 7.5 m) and height (30 and 40 m). Sillmats of different thicknesses (one and two stope widths) were considered using 7% binder content. Stope wall closure strains of 0.9% and 2% were also applied to assess the effect of arching on sillmat stability. Based on test results the effect of arching on stability has been for the first time quantified and guidelines for required sillmat thickness have been developed.
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