Predicting the Uniaxial Compressive and Tensile Strengths of Gypsum Rock by Point Load Testing

Excerpt

Uniaxial compressive and tensile strengths are considered key properties for characterising rock material in engineering practice. They are determined, directly and indirectly, as described by the International Society for Rock Mechanics (ISRM) (1985) and the American Society for Testing Materials (ASTM) (1986). The point load strength index (PLSI), an indirect strength test, has been correlated empirically with both the compressive and tensile strengths of rock. The point load test (PLT) may be applied to cylindrical specimens, either along the axis, or the diameter, but as noted by Chau (1998), the diametral PLT is preferred (Bieniawski 1975). In the PLT, rock specimens (of cylindrical, prismatic, or irregular form) are loaded between two platen contact points, and they fail by the development of one or more extensional planes containing the line of loading. According to recommendations by ISRM (1985) and the standards of ASTM (1986), these types of failure mode are regarded as valid, whereas deviations from them are treated as invalid. …