Abrasivity characterization of selected rock formations of pakistan /

Abstract

This study characterized the abrasivity potential and evaluated different rock abrasivity measurement methods on 51 rock units selected from different regions of Pakistan. For abrasivity measurements CERCHAR, LCPC and NTNU/SINTEF abrasion tests were adopted. Laboratory tests also included a complete suite of engineering rock properties performed on all 51 rock units as well as petrographic analyses along with determination of Schimazek’s F-value and Rock abrasivity Index (RAI). The CERCHAR tests were conducted on sawn (CAIs) and freshly broken (CAIfb) rock surfaces employing top and side viewing measurement methods at the stylus tip. This study statistically confirms the previous work on the influence of wear flat measurement methods and rock surface conditions on the CERCHAR Abrasivity Index (CAI) values. It was found statistically that CAIs and CAIfb values measured from top view of test stylus were 17 and 19 % higher, respectively, in comparison to CAIs and CAIfb values measured from side view of test stylus. The correlations of CAI with rock properties are also discussed. Further 33 sedimentary rock samples out of total 51 rocks were subject to CAI measurements and rock properties tests in saturated condition. Overall 79% of CAIsat values were less than CAIdry values, meanwhile 52% of CAIsat values showed significant reduction from CAIdry values in the statistical analyses of CAI results with significance level of 15% (α = 0.15) . The proposed correlation of CAIsat with CAIdry can be used to estimate CAIsat from laboratory tests where reported CAI is often CAIdry. This could lead into more accurate estimation of tool wear and related adjustments when CAI is used for estimation of tool wear when excavtion is done under wet rock condition. Moreover, a predictive model of CAIsat with saturated rock properties was also developed. This study also compared the results of LCPC dry and saturated tests for 20 selected rock types performed at 15, 30, 45 and 60 % water contents. Overall abrasivity decreased with the increase in water content with peak values attained at 15% and 30% water contents for low porosity and high porosity rocks respectively as compared to dry tests. Similarly, a gradual reduction in LCPC Breakability Index (BR %) was noted in the case of low porosity rock samples with the corresponding rise in water content levels. However for high porosity rocks the breakability first reduced abruptly at 15% moisture content in contrast to the tests conducted at 0% moisture content followed by a rise at 30 % water content and finally at 45% and 60% water contents the breakability dropped down steadily in comparison to the dry test values. Moreover, possible correlations of LCPC test results for all 51 rocks with rock properties were discussed. Finally a comparative study was performed on NTNU/SINTEF rock abrasivity device by varying the particle size of rock abrasion powder and test speed. The NTNU/SINTEF Abrasion Value Steel (AVS) test results showed a gradual decrease in abrasivity with the corresponding decrease in grain size of test fractions. Whereas, rise in the wear of test piece was observed at a test speed of 10 rpm as compared to the standard test speed of 20 rpm. Relevant correlations of CLI with CERCHAR and LCPC test results and rock properties were also included.