Strata Control Technology

Wollongong, Australia

Strata Control Technology

Wollongong, Australia

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Mills K.W.,Strata Control Technology | Garratt O.,Strata Control Technology | Blacka B.G.,Strata Control Technology | Daigle L.C.,Strata Control Technology | And 2 more authors.
International Journal of Mining Science and Technology | Year: 2016

An underground coal mine located in New South Wales has a target coal seam located 160-180 m deep directly below a 16-20 m thick conglomerate unit that has been associated with significant periodic weighting events on the longwall face. As part of the investigations to better understand the causes of periodic weighting at the mine, inclinometers capable of measuring horizontal shear movements through the full section of the overburden strata were installed ahead of mining at two locations approximately 1 km apart above the centre of two longwall panels. These inclinometers were monitored as the longwall approached each site. This paper presents the details of the installation, the results of the inclinometer monitoring at both sites, and the insights that these measurements provide for overburden behaviour about longwall panels. Horizontal shear movements were observed to develop on shear horizons that correlate closely across the two sites suggesting a mechanism that is consistent across a large area of the mine. Shear movements were observed to develop on a single horizon near the top of the conglomerate strata that was mobilised almost immediately after initial formation of the longwall goaf at a distance of 425 m ahead of the longwall face. © 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.


Puller J.W.,Strata Control Technology | Mills K.W.,Strata Control Technology | Jeffrey R.G.,CSIRO | Walker R.J.,Strata Control Technology
International Journal of Mining Science and Technology | Year: 2016

A coal mine in New South Wales is longwall mining 300 m wide panels at a depth of 160-180 m directly below a 16-20 m thick conglomerate strata. As part of a strategy to use hydraulic fracturing to manage potential windblast and periodic caving hazards associated with these conglomerate strata, the in-situ stresses in the conglomerate were measured using ANZI strain cells and the overcoring method of stress relief. Changes in stress associated with abutment loading and placement of hydraulic fractures were also measured using ANZI strain cells installed from the surface and from underground. Overcore stress measurements have indicated that the vertical stress is the lowest principal stress so that hydraulic fractures placed ahead of mining form horizontally and so provide effective pre-conditioning to promote caving of the conglomerate strata. Monitoring of stress changes in the overburden strata during longwall retreat was undertaken at two different locations at the mine. The monitoring indicated stress changes were evident 150 m ahead of the longwall face and abutment loading reached a maximum increase of about 7.5 MPa. The stresses ahead of mining change gradually with distance to the approaching longwall and in a direction consistent with the horizontal in-situ stresses. There was no evidence in the stress change monitoring results to indicate significant cyclical forward abutment loading ahead of the face. The forward abutment load determined from the stress change monitoring is consistent with the weight of overburden strata overhanging the goaf indicated by subsidence monitoring. © 2015 Published by Elsevier B.V. on behalf of China University of Mining & Technology.


Barbato J.,University of New South Wales | Hebblewhite B.,University of New South Wales | Mitra R.,University of New South Wales | Mills K.,Strata Control Technology
International Journal of Rock Mechanics and Mining Sciences | Year: 2016

Strain is an important parameter for assessing the potential for impacts on surface features due to mine subsidence. However, this parameter is also one of the most difficult to predict. Research is being undertaken with the objective to improve the currently available predictive methods for horizontal movement and strain at the surface. The methodology predominantly follows an empirical approach, using a large database of ground monitoring data, which was supplemented using numerical modelling. Predictive equations have been developed for the relative horizontal movements across various zones above longwalls based on the vertical subsidence and the influence of topographical features. These relative horizontal movements are then used as the basis to predict the distributions of strain within each of these zones. This paper provides an overview of the methodology and the current findings from this research project. © 2016 Elsevier Ltd.

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