Rainfall Infiltration into Unsaturated Soil

As a tropical country, Malaysia is in the region of residual unsaturated soil. The prolonged and high intensity of rainfall will affect the parameters such as pore water pressure and moisture content of soil. This paper presents the experimental test result of rain water infiltration into soil column for unsaturated soil. The main objectives were to study the effect of rainfall intensity and duration to water infiltration into the soil. In this study, two types of soils were used; gravelly sand and kaolin. Rainfall with designated intensities and durations were applied to the soil column apparatus. The soil column apparatus system involved three component; water supply system, soil column and instrumentation, and effluent system. The result showed that during wetting process, the value of pore water pressure was gradually increased until the rainfall stopped and drying process took place. The top section of soil column responds earlier than middle and bottom for both during wetting and drying process. The changes from high to low intensity give smaller value of pore water pressure for intensity type 2 for both soils. The result also shows that different length of tensiometer affect to small changes for both type of soil. Result of volumetric water content for both soil have a good agreement with the responds to pore water pressure. These shows that the middle section of soil column has the ponding condition where water infiltrates and stay longer at this section before its continue to infiltrate to bottom section.