ABSTRACT:
Rock mass classification developed as a tool to allow engineers and geologists to assess tunnel stability and support requirements during tunnel advance. In some circumstances little time or information is available for assessing rock mass conditions so classification systems developed to be a quick and easily used tool. Rock mass classification is a very attractive term for engineering design because it provides a single number to represent the rock mass. This single number has been related to rock mass properties such as unconfined compressive strength (UCS) and Young’s modulus, as well as input for Mohr - Coulomb and Hoek Brown failure criteria. Rock mass classification is a key component to many currently used empirical and numerical design methods and provides the engineer with a much needed tool to directly relate field data and observations with design methods. Classification systems have significantly advanced rock mechanics, however, their ease of use may also be hindering continued advance in the field
1 INTRODUCTION
Rock mass classification has evolved to satisfy several often contradictory goals:
1. A quick easily used field tool to assess tunnel stability and support requirements.
2. An accurate assessment of rock mass properties for underground tunnel design, open stope design as well as the design of surface excavations.
3. A repeatable assessment of rock mass properties.
The original goal of determining tunnel stability and support requirements meant that classification systems developed as a complete design package and included some measure of the environmental conditions driving instability. These factors included the Stress Reduction Factor (SRF) used in the Q classification system (Barton 1974) and joint orientation correction used in the RMR systems (Bieniawski 1976). When classification systems are used as input for numerical or empirical design methods that already take into account these factors, they should not be included in the rock classification system.
