Estimate of uniaxial compressive strength of hydrothermally altered rocks from northeastern Hokkaido, Japan, based on axial point load strength test results

Abstract

The purpose of this study was to clarify the relationship between axial point load strength and uniaxial compressive strength in hydrothermally altered rocks, which are typical of the soft rocks found in northeastern Hokkaido, Japan. The numbers of specimens tested were 1,755 rock specimens for the axial point load strength test, whereas 329 rock specimens for the uniaxial compressive strength test. These came primarily from the earth’s surface in ancient hydrothermal fields. The rock specimens underwent axial point load strength and uniaxial compressive strength tests using a laboratory testing machine with specimens in forced-dry and forced-wet states. The correlation between the axial point load strength and the uniaxial compressive strength was linear. The forced-dry and forced-wet states can be combined to giving a relationship in which the relation of axial point load strength (Is) and uniaxial compressive strength (qu) was qu = 12.9 Is in the soft rocks with axial point load strengths below 1.5 MPa. This relationship might be applied to on-site tests of rocks with natural moisture content. The number of tested specimens satisfied accuracy requirements, based on the coefficient of variation. The axial point load strength was strongly correlated with the uniaxial compressive strength. Therefore, the relationship between axial point load strength and uniaxial compressive strength established in this study was highly precise. We could calculate the uniaxial compressive strength from axial point load strength tests in the soft rocks only when their axial point load strengths were below 1.5 MPa.