Determination of uniaxial compressive strength using point load index of high grade metamorphic rocks from western Sri Lanka

Abstract

This research is focused on finding the correlation of unconfined compressive strength (UCS) with Point load Index (PLI) of gneissic rocks, and to propose proper correlating value, based on a study carried out for Sri Lankan Gneissic rocks. There has been an increasing use of the PLI as a measure of rock strength since its introduction in 1972. The small size and the simplicity of the point load tester have led to its use on site in many projects. The rock samples were obtained from three rock quarries in the Western Province. Using the results of laboratory testing of gneissic rocks under point loading as well as in Uniaxial Compression, and statistical analysis, different conversion factors relating UCS and PLI are determined for each quarry. The sample preparation and testing are conducted according to the A STM code. Exactly 206 individual test results, from 35 distinct rock units were used The conversion factor between UCS and PLI of the study is found to be between 9 and 14. The results of the study are useful to find the strength of rocks conveniently through point load testing.