Rock abrasiveness testing for tunnelling

The cerchar abrasiveness test for rocks is widely used in the French coal mining industry; it is being introduced in the British coal mining industry, and it is also beginning to be used to assess the abrasiveness of rocks for machine tunnelling. This paper describes an apparatus to perform the test for research purposes, discusses methods of abrasiveness testing, and presents preliminary results for some British rocks. The test apparatus, which was devised to meet almost all aspects of the cerchar test specification, was designed and made at the transport and Road Research Laboratory. Most rocks have proved suitable for testing, but it is not possible to use it for rocks that are too soft or hard. The results of test measurements for some British sedimentary, igneous and metamorphic rocks are provided. The following conclusions are reached: (1) the results of the cerchar abrasiveness test are highly correlated with Mohs' degree of hardness scale; (2) rocks with abrasiveness greater than 4 or 5 may produce high wear rates on tunnelling machine cutters; (3) in an application of the test to the South drive of the selby tunnels, in Yorkshire, England, a definite relation was found between the abrasiveness and quartz content of the rocks in a limited range of coal measures sediments. (TRRL)