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 censtructed 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 materia" ,zroperties in single or multi-strata ground along a proposed tunnel route.

Engineering geology plays an indispensable part in the planning and construction of tunnels. This is demonstrated by the construction of the Midge Hall Valley Sewer tunnel through Middle Coal Measures rocks in the vicinity of Rochdale, Greater Manchester.A three-phased site investigation was carried out, at the planning, design and construction phases of the project. These lead to the determination of ground reference conditions, the choice of tunnelling method and the target cost of the tender.Throughout the project good communication was maintained between the client, the engineer to the project and both the site investigation contractor and the tunnelling contractor. This invoked confidence in the prediction of ground conditions forward of the tunnel face, and in the excavation and support methods used during the works. This example demonstrates the high value of good quality engineering geological input throughout a high risk construction project such as tunnelling.