An Equation to Evaluate the Unconfined Compressive Strength of Rock from Splitting Tensile Strength Test Results

The unconfined compressive strength (UCS) of rock is a basic parameter for the design of foundations resting on rock. However, it is often very difficult to retrieve intact rock core specimens for the UCS test due to mechanical breaking or natural fracturing of the rock core during the drilling process. In such cases, it becomes obligatory to correlate UCS values based on the point load strength index test results. Correlation between the UCS and the point load strength index test results has been observed to be inconsistent in many instances and hence a need for another such correlation with a relatively higher degree of accuracy to predict UCS values of rock sample has been generated. An endeavor has been made to correlate the UCS value based on the test results of a splitting tensile strength test (STS) by conducting both the tests on various rock samples. Though the UCS test provides compressive strength and the STS test provides tensile strength of a rock, a dimensional analysis technique has been used to correlate these properties. The predicted UCS results are compared with the actual lab UCS test results to validate the mathematical equation thus developed. It has been observed from comparison that this equation can be used to predict UCS values from STS results with a fair degree of accuracy. Thus the Dimensional analysis has established a provisional rule-of-thumb to correlate the UCS with STS test results and further proved that, it is an easy and sufficiently accurate analytical tool.