Abstract
This paper is based on a prefeasibility project requiring initial estimates of support needed to stabilize excavations made in a rock mass. It is a typical engineering scoping study which sought for the necessary information on which a reliable decision on whether to proceed with the project or not could be made. The paper features the assessment of stability and support requirements of a combination of a metro tunnel, metro station and ventilation raisebore excavations. Bieniawski’s Rock Mass Excavability index (RME) was utilized to determine the advance rate expected for the raisebored tunnel. Principles of rock mass classification are utilized in the project. Rock mass classification (RMC) plays a pivotal role in the design of excavations in both civil and mining engineering. It is a quick and an uncomplicated powerful tool to assess stability of excavations as well as the support requirements of the same. Rock mass deformation properties can also be determined using RMC systems. While it is so easy to use them, one needs to have the requisite technical skills to comprehend the theory underlying each classification system together with its limitations. This approach in using rock mass classification systems minimize abuse and ensures maximum benefit from them. The author also briefly discussed some of the ways to address serious concerns about RMC systems.
1. INTRODUCTION
The mining engineering fraternity strives to achieve safe, fast and economic extraction of mineral resources. Rock mass classification is one of the powerful tools to this end. While Rock Mass Classification (RMC) techniques like Rock Mass Excavability (RME) index, Q system, Geological Strength Index (GSI), Terzaghi’s rock load approach, Bieniawski’s RMR system, Laubscher’s MRMR system, Potvin stability graph method, Barton’s QTBM, Mark and Molinda’s Coal Mine Roof Rating (CMRR) and the Rock Wall Condition Factor among others have gained wide spread use, they must be used with great care and caution if users are to get workable solutions from them. RMC systems are like a pencil handled in an artist’s hand calling for greater skill and experience in order to leave an artful impression. One needs to beware of the limitations of each system and its areas of applicability before attempting to use it. It must be noted that RMC systems have to work hand in glove with laborious engineering design in order to come up with a workable solution. RMC systems should complement more sophisticated and detailed design procedures [1]. In the goal to realise workable solutions in engineering including classification of rocks, [2] point out that technical skills are among major strategic issues to be considered. Like other approaches there is risk associated with making RMC approaches part of our designs. This risk has to make part of our decision criterion as advised by [3]. This way, RMC systems become reliable, fast, easy and much less complicated means of addressing design needs.
