2017 Volume 73 Issue 1 Pages 93-105
Because the present rainfall traffic regulation standard of expressways against rainfall-induced surface failure does not consider rainwater infiltration and deformation of a slope, appropriate decisions for road closure and its deregulation are sometimes difficult. To propose a new index aimed at the advancement of the present rainfall regulation standard, laboratory scale experiments as a fundamental study are conducted. Through a preliminary experiment, a possible mechanism of water infiltration and slope deformation was identified. According to this, slope deformation starts when the volumetric water content exceeds a quasi-saturation state, which is not a fully saturated state but a saturated state with entrapped air. After implementing laboratory experiments to confirm repeatability of the quasi-saturation phenomenon, two phenomena were confirmed. One is the repeatability of the quasi-saturation state in these model slope experiments. The other is that a process from a quasi-saturation state to slope failure is manifested in order of the quasi-saturation state, the saturation state, and the slope failure. When the relation between the variation of volumetric water content and the deformation was evaluated using an image sensing technology called template matching, it was confirmed that the slope displacement begins to extend after the volumetric water content exceeds the quasi-saturation state. The volumetric water content increases after the quasi-saturation state is exceeded because the increase in soil porosity due to variations in soil structure caused by seepage force. This indicates that there is no deformation when the volumetric water content does not exceed the quasi-saturation state. In addition, the quasi-saturation state is a possible index for predicting rainfall-induced surface failure. However, to apply real slope monitoring for practical use along expressways, additional laboratory scale experiments utilizing medium and large-scale slope models are required, in addition to the continuation of the on-site slope monitoring test.