STUDY OF CERCHAR ABRASIVITY INDEX AND POTENTIAL MODIFICATIONS FOR MORE CONSISTENT MEASUREMENT OF ROCK ABRASION
Open Access
- Author:
- Ghasemi, Amirreza
- Graduate Program:
- Energy and Mineral Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 10, 2010
- Committee Members:
- Jamal Rostami, Thesis Advisor/Co-Advisor
Jamal Rostami, Thesis Advisor/Co-Advisor - Keywords:
- excavation
rock
cerchar
abrasivity
abrasion
tunnel - Abstract:
- Tool wear is an important parameter in mechanized tunneling and is highly affected by rock abrasiveness. There are numerous tests to identify the rock abrasivity. One of the widely used rock abrasion tests is the Cerchar abrasion index (CAI). This test is used for estimation of bit life and wear in various mining and tunneling applications. The test is simple and can be considered for field applications. However, there are some discrepancies in the test results related to the equipment used, surface condition of rock samples, operator skills, and procedures used in measurement of worn out surface (wear flat). This study discusses the background of the test, reviews the testing parameters and their impact on testing as noted in previous studies, and examines the impact of the different parameters on Cerchar testing. Seven rock types ranging from abrasive to non-abrasive were in the testing program. Pins with different hardness were used on rough and sawn surfaces of the selected rock samples. Geomechanical properties of these samples were also measured. Cerchar values of different pins were compared and formulas offered by some researchers for conversion of the CAI measurements between pins of various hardness were found to be satisfactory. It was confirmed that the rough samples have higher Cerchar values as compared to sawn-cut samples. Good correlation between the Cerchar value and the Compressive strength and equivalent quartz content in rough samples were achieved. Tests were performed on three rock types with different speeds and the results proved that the test speed does not change the results significantly. By using various loads on the pin, it was concluded that the applied load linearly affects the Cerchar value. Meanwhile to mitigate the issue of operator sensitivity and errors associated with measurement of the worn out surface, a new method for measuring the tip loss, which was already developed by NTNU, was used. This method uses the side view of the pin to measure the tip loss. It was proved that this method can decrease the operator sensitivity of the measurements. A new device was introduced in an attempt to address some of the shortcomings of the Cerchar test. The test involves use of a 90-degree cone pin on a sample that is placed on a lace. The rotation of the lace allows for control of the length of the scratch, whereas the arrangement of the tool allows for varying the amount of load placed on the tip. Some preliminary tests were performed on seven rock types and initial results do not show a good correlation with Cerchar measurements. Another set of tests were performed on sawn quartzite with varying applied loads and test durations. It was concluded that applied load is linearly correlated with the tip loss. As in soft rocks, the pin tends to penetrate into the rock. It is more reasonable not to apply higher loads on the pin to prevent excessive penetration and possibly failure of the sample. The results also proved that the wear mainly occurs in the first few rotations and therefore a long test duration is not needed.