The purpose of this study was to clarify the relationship between irregular lump point load strength (PLS) and uniaxial compressive strength (UCS) in hydrothermally altered and least altered rocks, which are typical of the soft and semi-hard rocks found in northeastern Hokkaido, Japan. The numbers of specimens tested were 2,710 rock specimens for the irregular lump PLS test, whereas 312 rock specimens for the UCS test. These came primarily from the earth's surface in ancient hydrothermal fields. The rock specimens underwent irregular lump PLS and UCS tests using a laboratory testing machine with specimens.
The correlations between the irregular lump PLS, which was calculated by the formula of Hiramatsu et al. (1965), and the UCS were linear. The relationships between irregular lump PLS (Is(i)) and UCS (qu) were qu = 5.3-5.4 Is(i), in the soft and semi-hard rocks with an irregular lump PLS below 8 MPa. These relationships applied to on-site tests of rocks with natural-moist state. The number of tested specimens satisfied accuracy requirements, based on the coefficient of variation. The irregular lump PLS was strongly correlated with the UCS. Therefore, the relationships between irregular lump PLS and UCS established in this study were highly precise. We could calculate the UCS from irregular lump PLS tests in the soft and semi-hard rocks only when their irregular lump PLS below 8 MPa.
