Abstract
The uniaxial compressive strength data is used in the mine design to develop input parameters for rock mass classification. The purpose of this study is to develop a correlation between the compressive strength and other index tests for various rock units for a proposed mine. The various index tests were performed to develop the compressive strength value to be used in the design of the mine during prefeasibility-level study. The point load tests (PLT), Schmidt Hammer tests (SHT) and density tests were also performed along with uniaxial compressive strength tests (UCS) in order to develop a correlation among the compressive strength and index tests. About 700 point load tests, 155 Schimdt Hammer tests and 70 uniaxial compressive strength tests for rock cores retrieved from the investigation site were performed. The SHT and density tests were performed for all rock cores that were tested for UCS. It was not possible to test the PLT and UCS using the same rock core sample. The PLT tests were performed using both diametral and axial test methods. The point load test data was broadly classified into two categories based on the failure surface. The intact failure strength represented the failure plane through intact rock while structural failure strength represented failure through preexisting bedding, fracture or joint plane.
The rock groups at the site was broadly classified into three (3) rock group category (A-Limestone, B-Weak rocks and C-Breccia) based on point load strength. Only intact failure point load strength data was used to find the relation between PLT and UCS. The point load strength for Breccias was the highest while the same for Weak rocks was the lowest. The mean PLT Is (50) values for three major rock categories Limestone, Weak Rocks and Breccias was 521 psi (pounds per square inch), 232 psi and 1334 psi respectively. The mean rebound number values for three major rock categories Limestone, Weak Rocks and Breccias was 58, 50 and 60 respectively. The relationship between PLT and UCS was established by comparing the mean strength value for each rock group. There is a good relationship found between compressive strength and point load index for Limestone rock group. The ratio of mean UCS to mean PLT for this rock group is 24. This ratio has been presented in the literature for many rock groups. On the other hand the UCS/PLT ratio was found to be 16 for Weak rock and 10 for Breccias. The point load strength from dimetral tests was found to be lower than axial tests. A good relationship is also found between density and UCS. This relationship is nonlinear and is better represented for Breccias. The relation between hammer test and UCS is found to be nonlinear for all rock groups. The correlation between UCS and SHT was not very good.
