Cerchar Abrasivity test in tunnelling: a modified version for evaluating the performance of conditioning agents as wear preventers

The Cerchar Abrasivity test is used for assessing the abrasion of rock due to its simplicity and fast execution and it is considered one of the main wear indexes in tunnelling. Despite in standard condition the test is performed on a dry surface of a rock sample, this study introduces the possibility to carry out the test on a conditioned surface. In details, this work compares the Cerchar Abrasivity Index (CAI) results of rock specimens subjected to three conditions: dry, saturated with water, and saturated with a polymeric slurry. First, dry samples were prepared according to the standard procedure while the second and the third sets have been planned in order to simulated the injection of water and polymers respectively, a practise that is nowadays accepted in construction site where rock TBMs are adopted. Results put alight that the use of conditioning such as water and polymeric slurry on the rock leads to a reduction of the wear potential of the rock itself. Notably, the rock specimen treated with the polymer slurry exhibited the lower value of CAI (with a reduction of 34% compared to the dry sample). The potential benefits of use specific preventing-wear polymer in rock excavation is in conclusion analysed.