Cerchar scratch test
The Cerchar scratch test is a very common test which used for laboratory assessment of hard rock abrasion. For economic reason, the problems in the preliminary stage of hard rock underground project are choice of suitable excavation method; excavation rates estimations and tool consume costs. In this stage of a project, geotechnical engineers are face with difference geotechnical parameters in order to predict excavation rates and tool consumption. In addition to other relative parameters for excavation rate and tool consume prediction (Thuro & Plinninger, 2002), the Cechar scratch test and the derived parameter, the Cerchar Abrasiveness Index (CAI), represent one of the most common testing procedures for the laboratory research of hard rock abrasion (Plinninger and Thuro, 2004). The Cerchar scratch test (1986) was developed in France in the middle of 1980s. It aims to predict the abrasion of cutters which on the tunnel boring machines. This test base on a steel needle with defined geometry and hardness which scrape over 10 mm in rough rock sample under a static load of 70 N. Then, the CAI calculates from the measured diameter of the result of abrasion flat on the testing needle. The CAI can be a standard parameter for hard rock classification.
Plot of CAI values gained on the same rock and plot of CAI versus testing length samples after different surface formatting.
The data shows a relationship between surface conditions. The flattening of the regression curve show an increasing of surface roughness with increasing CAI. In low CAI, where tests on rough surfaces and saw cut one . The tests on very abrasive rock samples show higher CAI values on rough samples than saw cut surfaces. Setup
This setup holds the rock specimen and a testing lever that is directly connected to the steel pin. The steel pin is loaded with a static force of 70 N and scratched over the rock surface by moving the lever at a velocity of 10 mm/sec....
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