Preliminary Investigation into Measurement While Drilling as a Means to Characterize the Coalmine Roof

Manoj Khanal,Bongani Dlamini,Johnny Qin,Baotang Shen

doi:10.3390/resources9020010

Abstract

The variable nature of the coalmine roof poses a challenge to roadway stability during underground coal mining. There have been fatalities and financial losses in the coal mining industry due to roadway failures and roof falls. Generally, the geotechnical and geological data gathered from exploration boreholes, which are drilled at considerable distances from each other, are used to characterize the thickness and quality (including strength) of the coalmine roof. This process provides a limited number of samples that cannot represent the discontinuous nature of the strata in the coalmine roof nor can they form reliable inputs to a digital model of the rock mass component of the digital mine. Gaining confidence in the strata properties of the coalmine roof is necessary for the modelling, design, and maintenance of roadways. The paper describes the progress of the ongoing work to investigate the monitoring while drilling (MWD) concept for characterizing coalmine roofs. Large-scale drilling experiments in synthesized sandwiched rock samples without interfaces were carried out. The drilling response data were analyzed to identify whether the drill data differentiates the various strengths associated with the rock samples. The initial results show that the drilling data can differentiate the synthesized rock samples.

Highlights

A major cause of roof instability in underground coalmines is the uncertain variation of the coalmine roof
The geotechnical and geological data gathered from exploration boreholes, which are drilled at considerable distances from each other, are used to characterize the thickness and quality of the coalmine roof
It was found that Australian underground coalmines appear to lack a fully integrated measurement while drilling (MWD) system for roadway development [1], so applied research into the topic is required

Summary

Introduction

A major cause of roof instability in underground coalmines is the uncertain variation (for example, thickness, competence, discontinuities) of the coalmine roof. The geotechnical and geological data gathered from exploration boreholes, which are drilled at considerable distances from each other, are used to characterize the thickness and quality (including strength) of the coalmine roof This limited data cannot capture the local variability presented in the coalmine roof. If it was possible to reduce the uncertainty by measuring and analyzing various drilling parameters for roof bolting to interpret and gain confidence in the coalmine roof during roadway development, it would be possible to optimize roof support designs and improve TARP responses. This information would be valuable in generating a reliable digital model of the rock mass surrounding the mining process, an important component of a ‘digital twin’ of a mining operation. It was found that Australian underground coalmines appear to lack a fully integrated measurement while drilling (MWD) system for roadway development [1], so applied research into the topic is required

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