Seepage Responses in Soil Subjected to Rainfall

Abstract

Landslides triggered by rainfall are widely known disaster related to the interactions between hydrological responses and change in strength of the sloping ground. The infiltration of rainwater into the soil results in increment of soil water content, hence the drop of shear strength and factor of safety against slope failure. Understanding this interaction is vital to enhance the landslides warning system such that mitigation of landslide disaster can be performed effectively. This research investigated the seepage response in the soil by one-dimensional infiltration model under 3 rainfall conditions : 1) Rainfall intensity was less than permeability coefficient of the soil, 2) Rainfall intensity was close to permeability coefficient of the soil, and 3) Rainfall intensity was higher than permeability coefficient of the soil. Soil samples used in this study were gathered from the landslide warning station ; Ban Khlong Sathon, Wang Mi Sub-district, Wang Nam Khieo District, Nakhon Ratchasima Province. The test found that, under the 1st rainfall condition, the change of soil volumetric water content can be divided into two phases : infiltration phase and rising of water table phase. The infiltration phase involved the downward movement of the wetting front. In this phase, the water content increased from the initial value of the volumetric water content ( wi ) to the final volumetric water content called volumetric water content behind wetting front ( wb ) to reach saturated water content ( sat ). When the wetting front reaches to the impervious layer, the water content in the soil will increase due to the rising of water table. The magnitude of  wb increases with increasing the magnitude of rainfall intensity. The magnitude of  wb is equal to  sat when the rainfall intensity is equal to the permeability coefficient of the soil. In addition, the results showed that the wetting front velocity also depends on the rainfall intensity.