Relationship between point load strength index and uniaxial compressive strength of hydrothermally altered soft rocks

摘要

The boundary between hard and soft rocks has been defined by various organizations. For example, one definition places the boundary at a uniaxial compressive strength (UCS) of 25 MPa as mechanical properties [1,2]. On the other hand, in geological fields, for example, soft rocks are primarily Cenozoic sedimentary rocks and hydrothermally altered and weathered rocks of hard rocks [3]. The strength of fresh rocks and altered rocks, including hydrothermally altered or weathered rocks, is generally evaluated based on UCS. However, rock core pieces for UCS tests cannot always be obtained from outcrops of faulted, jointed or cracked rock masses. In these cases, the point load strength (PLS) test is a convenient and effective alternative to the UCS test, because it can be done promptly using on-site testing equipment with various shaped small rock specimens taken from outcrops or floats. Provided that we can calculate a UCS estimate from a PLS value, the PLS test can lead more convenient and cheaper [4-6].Many researchers have already studied the relationship between the PLS index and UCS.