ABSTRACT
The description of the rock mass with reference to major geological structures.
The orientation, nature, spacing and persistence of discontinuities.
Degree of weathering.
The presence and orientations of fractures and discontinuities in rock masses exposed in a surface mining excavation are likely to have a great influence on both slope stability and blasting efficiencies. The classification of rock materials requires detailed investigations which are of interest to the design engineer. In designing a safe mining excavation, an engineer rest take a number of decisions regarding face support and orientation based on the evaluation of local strength and structural conditions encountered. The description of rock masses requires information additional to the properties of the rock material, discontinuities and other characteristics of engineering importance. Such information involves the acquisition of the following data:- A critical review of rock mass classification systems and their application to surface mine excavation design and stability analysis is presented. The field investigation techniques for collecting rock mass data are described together with the techniques of analysis and presentation of data. Laboratory tests are carried out to determine intact rock strengths and deformation parameters of rock. The paper presents two case studies from the British hard rock surface mining industry to illustrate the application of the rock mass classification system to stability analysis and excavation design.
INTRODUCTION
Stability and blasting efficiency of rock masses in surface mines are governed by the presence and orientation of discontinuities and rock mss properties. In this paper, the Geomechanics Classification and Q System for Rock Mass Classification have been applied to evaluate both the blasting efficiency and the stability status of a mining excavation. To determine classification parameters, firstly field studies have been carried out for geological data collection, rapping of discontinuities and assessment of rock mss conditions which include RQD and weathering. Secondly extensive laboratory tests were carried out to determine the intact rock properties such as uniaxial compressive strength, shear strength, Poisson's ratio and modulus of elasticity. Since various parameters have different degrees of importance on blasting and stability, the relevant classification systems have been applied with modified adjustment factors for these purposes. Results from stability evaluations indicate that wedge, toppling and planar failures are the most likely modes of instability. The results of classification systems to the blast design can show in a semi-quantitative manner that rock mss properties and structural geology affect blasting efficiency in hard rock surface mines.
RESEARCH APPROACH AND PROGRAMME
Field measurements for the determination of structural discontinuity characteristics and weathering.
Laboratory investigation of rock properties for intact rocks and joints.
Mapping orientation, frequency of discontinuities and graphical presentation of data.
Application of rock mass classification systems.
Consideration of calculated values and optimization of the quarry faces for stability. Also to provide the most efficient fragmentation, toe and backface conditions
The research approach to the evaluation of stability and blasting efficiency in hard rock surface mines is based on the following steps:-GEOLOGICAL DATA COL T.RCTION AND STRUCTURAL GEOLOGY
The purpose of mapping is to orientate the bench profile in space.
