Abstract
It happens occasionally that new slopes or tunnel walls fail due to swelling of mudstone or claystone in consequence of water sucked. In this paper, various mechanisms of such failures have been investigated, and their causes are classified into the following 3 main cases.
(1) Deviatoric stress may have been generated in the mudstone or claystone due to the unisotropical expansion caused by the sucking of water. In order to examine the hypothesis stated above, some samples of mudstone from the deluvial layer situated about 180m beneath the surface of Osaka City and of claystone from Maibara Pass have been tested. In these tests, it has been shown that the swelling strain perpendicular to the bedding is larger than that parallel to the bedding. Accordingly, if the stress on the mudstone or claystone is decreased under a nearly confined state, the stress generated in the stone becomes unisotropical. If the deviatoric stress thus generated reaches the strength of the stone, failure takes place in the stone.
This strain or stress due to the swelling increases with time, and the rate of increase can be estimated by applying the expansion coefficient of the rock. Moreover, the capability of sucking water of the mudstone or claystone has been measured by suction-measuring device.
(2) The failure of the structure of the rock may have been caused by the local unequal expansion of the minerals contained and the fine seam of different materials. To observe the phenomena that have occurred in the rock when the rock has sucked water, micrometric expansive deformation will be measured by means of a microscope.
(3) The failure of the stone may have occurred in consequence of ununiform swelling due to the unequal distribution of sucked water.
