Abstract

The assessment of rock material properties is a critical element in any site investigation for the planning and construction of a tunnel through rock strata. This is irrespective of the number of rock strata involved and crucial to the determination of ground reference conditions as detailed in CIRIA Report No. 79 (1978).

An extensive suite of laboratory tests is combined with a comprehensive literature search in order to investigate the interrelationships between some commonly cited rock parameters. The suite includes Shore Scleroscope Rebound Values and results from a modified form of the Cerchar Abrasivity Test. In addition, the benefits from mineralogical analyses of rock samples are considered.

Rock material strength and hardness, with regard to common tunnel excavation techniques is found to be a combination of shear and tensile strength and can respectively be designated as cutting strength and abrasivity. An overall classification system is proposed which incorporates these parameters into an unambiguous notation in order to clarify test data and facilitate interpretation. By an appraisal of each testing technique in respect of relative costs and applicability to rock failure under machine excavation forces an incremental approach for rock testing programme is constructed in the form of a flow chart. The model proposes how the efficiency of current test programmes can be improved thus enabling more confident predictions of material properties in single or multi-strata ground along a proposed tunnel route.

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