Numerical Assessment of Rainfall Infiltration into Soil Column for the Unsaturated Layered Residual Forest Soil

Abstract

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.