The rock cutting technology has been developed quickly in the last century. However, the cutting of hard and abrasive rocks still has some problems such as low penetration rate and high wear rate of cutting tools. If the rock is abrasive, in addition to the high cost due to cutting tool wear, the replacement of tools causes considerable downtimes. Therefore, the understanding of the abrasivity of rocks is very important for the excavation projects. In this study, the effect of strength and mineralogy on the Cerchar abrasivity index (CAI) was investigated for igneous rocks collected from the ten different locations. First, the uniaxial compressive strength and the Brazilian tensile strength tests were carried out. Then, the CAI tests were performed on the samples. The quartz and feldspar contents were also determined by mineralogical analysis.
The test results were evaluated using the regression analysis. First, quartz plus feldspar contents were correlated to the CAI values. A strong correlation was found between the CAI and the quartz plus feldspar content. The correlation between the CAI and rock strength is not strong. Multiple regression analysis was also performed by including rock strength and the quartz plus feldspar content to the analysis. The correlation coefficient of the multiple regression model is slightly higher than that of the simple regression model. Concluding remark is that the evaluation of the abrasivity characteristics of igneous rocks should be further investigated by increasing the number of tested rock types and including the textural properties to the analysis.
The abrasivity is one of the important properties of rocks, which must be taken into consideration in excavation or drilling projects. It may highly affect the cost and schedule of the projects performed in abrasive rock mass. If the rock is abrasive, the replacement of tools causes considerable downtimes in addition to the high cost due to cutting tool wear. On the other hand, in the abrasive grounds, wear can also occur on several parts of the excavation machine (Nilsen et al., 2006 and 2007). Another important issue is that high rock abrasivity coincides frequently with higher rock strength. In such cases, for TBMs, the continuous application of high cutter load for the desired penetration will cause of bearing problems in discs. A failed bearing will lead to flattening of the disc at the face and the ensuing domino effect can cause a full wipe out of the cutters at the face in a very short time, if not detected/intercepted by the operator quickly. (Rostami, 2016). Therefore, the understanding of wear mechanism of cutting tools and various machine components is important for the planning and cost estimation of excavation projects.