Abstract
Slaking phenomenon lowers the strength of rocks in cut slopes. In Shikoku, the slaking phenomenon is quite prevalent, especially in the Izumi Group where shale rocks containing expansive clay minerals undergo slaking easily. X-ray diffraction tests, however, show no expansive minerals in the shale, which means the slaking of shale is not only due to the swelling of the expansive minerals. Lab tests such as x-ray diffraction tests, analysis of water properties, etc. revealed that the shale undergoes slaking easily because mica and feldspar in it undergo structural changes in presence of water and due to loss of cementation by amorphous minerals.