Abstract. Rainfall especially in tropical region caused infiltration to the soil slope. The infiltration may change pore water pressure or matric suction of the soil. The event of rainfall infiltration into soil is a complex mechanism. Therefore, the main objectives of this research paper is to study the influence of rainfall intensity and duration that changed pore water pressure to soil. There are two types of soils used in this study; forest soil and kaolin. Soil column apparatus is used for experiments. Rainfall were applied to the soil and result for 3, 6, 12, 24, 72, 120 and 168 hours were retrieved. Result shows that for the both types of soil, the negative pore water pressures were increased during wetting process and gradually decreased towards drying process. The results also show that pore water pressure at top part was increased greatly as the wetting process started compared to the middle and bottom part of the column.
Infiltration caused by rainfall leads to the changes of moisture content and pore water pressure of the soil. These changes indicate the behavior of the soil especially during wetting and drying due to rainfall. This paper describes the numerical analyses and result of rain water infiltration into soil column using SEEP/W (Geo-Slope International, 2004). The analyses were using three types of soils.Two types of soils were commercially obtained;siltyand gravelly sand, while another soilsample obtained from UniversitiKebangsaan Malaysia (UKM) forest. The main objectives are to describe the rainfall infiltration behavior into unsaturated residual forest soil, using one-dimensional soil column model, and the effect of rainfall intensity and duration to the infiltration process for the soils. The soil properties used for that analyses such as soil water characteristic curves (SWCC), and hydraulic conductivity were obtained from the laboratory works. The study was performed for one, three, and six hour flux for all types of soils.Results of volumetric water content show that water infiltration in silty and gravelly sand aremore rapidly than forest soil. The upper layer of soil column experienced greatly increased of volumetric water content compare to the other layers.In addition, pore water pressure for siltyand gravelly sand has also greatly increased from negative towards positive value for one and three hour rainfall compared to forest soil. Therefore, as the water infiltrates,initially dry soil will gradually increase both volumetric water content and pore water pressure as an event of rainfall is applied.
Failure of soil slope is mainly due to infiltration of rainfall. The complexity of rainwater path infiltrate soil slope can be predicted using commercial software, and volumetric moisture content at the infiltrated slope area can be measured by Time-Domain-Reflectometry (TDR). Prediction of rainwater path is based on parameters obtained by laboratory works, and volumetric water content using TDR can only available at the point of insertion. In this research, an innovative method called Electrical Capacitance Volume Tomography (ECVT) was used in geotechnical engineering application in determining the real-time imaging of rainwater infiltration into unsaturated soil slope. This method also achieves permittivity value through the experiments and converted to volumetric water content using equation. A soil sample obtained from slope failure around National Defense University of Malaysia (NDUM) campus during monsoon season was used in the research. The results revealed real-time 3 dimensions (3-D) images of rainwater infiltrated into soil slope were produced through image reconstruction method of ECVT. Volumetric water content was also achieved using permittivity value attained by ECVT result. Images which permittivity indicated the infiltration of rainwater through soil slope were clearly shown in the results. This innovative technology is expected to improve the understanding of soil slope behavior especially in for rainfall infiltration that relates to soil stability.
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