Study on the Correlations Between Abrasiveness and Mechanical Properties of Rocks Combining with the Microstructure Characteristic

Abstract

Rock abrasivity has become one of the necessary parameters for mechanical excavation of rock in the tunnelling industry (Wijk 1992; Hassanpour et al. 2011). The Cerchar abrasiveness test is widely used to assess the rock abrasivity. The test features a steel pin of specified shape and quality that is scratched over 10 mm of the specimen’s surface. The pin has a sharp conical point with cone angle of 90 . A static force of 70 N is loaded on the pin and the test is carried out by moving the steel pin at a prescribed velocity on the testing surface. The Cerchar abrasiveness index (CAI) is calculated by multiplying the mean value of the wear flats stated in units of 0.01 mm by 10. The testing velocity is reduced from 10 mm/s of ‘‘Cerchar apparatus’’ to 1 mm/s of ‘‘West apparatus’’ to accommodate the controllability of the testing velocity (West 1981, 1989; Michael et al. 2014). It was concluded in the literature that CAI was not only related to the abrasive mineral content alone but also influenced significantly by the rock strength (AL-Ameen and Waller 1994). The equivalent quartz content (EQC) alonewas found to be not enough to interpret the abrasion values of the Cerchar scratch test (Plinninger et al. 2003). It was found that some technical factors had impact on the test result of the Cerchar scratch test. CAI wasmainly influenced by the rock’s deformability and the content of abrasive minerals (Plinninger et al. 2003). Size of quartz grainswas proved to be very important to the scratch tip wear. Smaller quartz grains gave low wear rate and larger grains gave higher rate (Beste et al. 2004). The relations between CAI value and petrographic properties of Coal Measures Rocks were examined and a good linear relationship between CAI and average quartz grain size parameters was revealed (Yarah et al. 2008). Many factors, including pin hardness, surface condition of specimens, and petrographical and geomechanical properties, were examined to study the influence of various parameters on Cerchar testing (Jamal et al. 2014). So far, there is little knowledge about the quantification of microstructure as well as the effect of microstructure characteristics on the abrasiveness of rocks. Microstructure coefficients are defined and integrated with the mechanical parameters in this study to account for the combined effects on the abrasiveness of rocks. The abrasiveness apparatus used in this study has been improved based on the previous test apparatus. The horizontal movement of the steel pin, which is driven by step-servo motor, can be controlled accurately through software (Fig. 1).