A review of rock abrasiveness testing for tunnelling

The abrasiveness of rock is one of the factors of concern to the engineer considering the excavation of a tunnel in rock by either a full-face or a partial-face tunnelling machine. For even if the rock is not too strong for mechanised excavation, wear of the tools of the tunnelling machine if the rock is abrasive may render the operation costly. The strength of the rock is commonly assessed directly by a test such as the uniaxial compressive strength test carried out on cylindrical specimens, or indirectly by a test such as the Schmidt hammer test carried out on an exposed rock face or on the surface of a core sample. There is, however, no accepted standard test to assess how abrasive a rock is although a large number of different tests are in use. For tunnel excavation purposes what is needed is an abrasiveness test that can be carried out on samples of rock obtained during the site investigation and which will enable prediction of likely tool or cutter wear to be made. This paper reviews the types of test of abrasiveness that have been put forward, assesses their advantages and disadvantages from the tunnel excavation point of view, and makes recommendations.