Abstract
The purpose of this study is to clarify the mechanical properties of hydrothermally altered rocks found in northeastern Hokkaido, Japan, based on point load strength test results.
Rock specimens are hydrothermally altered soft and semi-hard rocks, including volcaniclastic rocks of the Upper Miocene Series. The modes of occurrence of these hydrothermally altered rocks were examined in the field, and the hydrothermal alteration minerals in the rocks were identified primarily by X-ray powder diffraction. The hydrothermal alteration zone can be divided into nine more specific zones on the basis of mineral assemblages of hydrothermally altered rocks. 1,523 rock specimens were collected for the axial point load strength test, whereas 1,869 rock samples for the irregular lump point load strength test. These came primarily from the earth's surface in ancient hydrothermal fields.
For rock specimens, the axial and irregular lump point load strength tests were performed using a laboratory testing machine with specimens under forced dry- and forced wet-states.
K-feldspar zone rocks had the largest axial and irregular lump point load strengths, followed by alunite-quartz zone rocks. Mixed-layer mineral zone and smectite zone rocks had the smallest. Illite zone and clinoptilolite zone rocks tend to be small.
Alunite-quartz zone rocks had the smallest point load strength decrease ratio. Mixed-layer mineral zone rocks, on the other hand, had the largest. Excess of 50 % at low point load strength decrease ratio of hydrothermal alteration zone rocks is related with surface water and ground water, suggesting possibility of landslides.
The point load strength test is very convenient and effective, because it can be done promptly using on-site and laboratory testing equipment for small rock specimens having various shapes taken from outcrops or floats.
