ABSTRACT
The research work outlined in this paper examines the importance of laboratory testing of friable coal measure rock for the stability assessment of surface and underground excavations. A pre-requisite for the stability analysis of mining excavations is a knowledge of strength and deformation parameters of rock surrounding an opening. The importance of the evaluation of strength and deformation parameters of rocks for a geotechnical investigation has been identified and index testing of rock for appraisal of strength at a field site is critically examined. A critical appraisal of various index testing techniques for intact coal measures rock has been made. The types of index tests available have been classified by the authors as strength properties tests, Intrinsic Properties Tests, Second Order Parameters and Rock Quality Designation (RQD). A critical review of index testing methods is presented. These tests are necessary for quick estimation of strength and deformation parameters of rocks for the purpose of design of structures in rock, and for the prediction of the stability performance of mining excavations.
INTRODUCTION
In recent years, the quest for alternatives to imported oil has led to the prospecting and feasibility study of new coal deposits in various parts of the world e.g. Canada, Australia and South Africa. Some of the developing countries are planning to double their existing output in the next five years. One of the prime requirements of the feasibility studies of large mining projects is the stability evaluation and the support design of mining excavations. The data necessary for the design of mining excavations are a knowledge of the strength and deformation properties of rock surrounding an excavation. The geotechnical information for a new mining project, during a feasibility study, must therefore be obtained from the data available from exploratory boreholes. In the past few years, a large number of index tests have been developed which could be applied to borehole cores. The object of this paper is to examine the application of index testing for synthesising the strength and deformation parameters of the surrounding rock for the stability assessment of Coal Measures excavations. The use of open hole wireline logging techniques to predict strength parameters is also discussed.
INDEX TESTING TECHNIQUES
In the past few years a large number of index tests for intact rock have been devised. Table 1 critically examines some of the index tests applicable to friable Coal Measures and summarizes the test requirements, sample size and shapes, loading geometry, loading rates and limitations of each type test. The Brazilian test has been extensively used for determining tensile strength and is applicable to the classification of rock mass by strength for drillibility, rock breakage and crushing studies. The impact strength test is devised by Evans (1973, p 132) and has been used to estimate resistance of rock to degradation and is applicable to rock workability studies. The cone indentor hardness test has been developed by the National Coal Board, Mining Research and Development Establishment (MRDE) for assessing rock strength in deep coal mines.
