Abstract
Estimates of rock tensile strength are a standard part of most laboratory testing programs, which usually include unconfined compressive strength tests as well as estimates of Young’s Modulus and Poisson’s ratio. Non-destructive tests for rock density, as well as dynamic values for Young’s Modulus and Poisson’s ratio, are also frequently conducted with a standard testing program. More extensive testing programs may also include triaxial testing for estimating m intact for m & s failure criteria and shear testing of joint surfaces.
This paper includes a comparison of direct tensile tests and Brazilian tests for estimating the tensile strength of Lac du Bonnet Granite. This rock was chosen for testing because it has already received quite extensive testing and is fairly consistent in its’ properties. The rock was obtained from a granite quarry in Manitoba.
Test results indicated that direct tensile tests gave results approximately 15% lower than Brazilian tests, with a much lower standard deviation. The testing procedure requires specialized loading platens for each size of core tested and the cost for each test is more than a Brazilian tests, however, the results are more consistent than Brazilian tests suggesting fewer tests would be required. The authors suggest that while further testing is required, direct tensile results should be considered as a viable economic option for estimating rock tensile strength.