Ground behaviour and rock engineering tools for underground excavations

Various design tools and methods can be applied to the engineering, planning and construction of underground projects in rock. A huge variety of rock masses and ground conditions may exist and, for excavations like tunnels, caverns, or shafts, it is important to apply relevant tools that cover the actual rock mass and ground conditions encountered. The aim of this paper is to clarify the limits of these tools and indicate the ground conditions for which they work best. Definitions are presented for the main types of behaviour of the ground. The triggering effects are grouped into gravity driven, stress induced and water influenced. The last group includes the special case of minerals susceptible to water. The main types of rock engineering tools are briefly described, indicating their limits. A matrix is presented showing their applicability to various types of ground behaviour. It is recommended that engineering judgement should always be applied to the output from the relevant design tool, especially for weakness zones such as faults, where most of the available tools have limited suitability. The importance of experience and knowledge of both the structure of these tools and the conditions where they work best is pointed out. It is shown that empirical methods based on classification systems work best in blocky ground. For these, the quality of the input parameters and an understanding of their limitations are regarded as a pre-requisite for good workmanship.

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