An investigation of the accuracy of the use of point load index test results to predict the unconfined compressive strength of Calp limestone in Ireland

摘要

Discontinuities including fractures, bedding and joints within bedrock can lead to challenging rock coring conditions, frequently resulting in a limited amount of intact rock being recovered as part of standard site investigations. This can result in very low numbers of suitable samples for unconfined compressive strength testing (UCS) being available. In the absence of UCS test results, or in the absence of a sufficient number of test results, point load index test (PLT) results of the recovered core are frequently used to estimate the UCS value. This approach relies on the accuracy of a correlation factor used to predict the UCS value from the PLT. This paper sets out the results of several years of work to investigate the reliability of this method in modelling the UCS value in the Calp Limestone formation. This work collates results from several hundred boreholes drilled in the Calp Limestone formation in eastern Ireland, UCS testing and point load testing were carried out on the cut off pieces of rock core produced in preparing the actual UCS sample. Estimated UCS values predicted using results from point load tests carried out on the cut offs are compared to the actual UCS values recorded. The data demonstrates that commonly used industry PLT - UCS correlations do not reliably predict the UCS value.