PENGARUH INFILTRASI TERHADAP PERUBAHAN PARAMETER TANAH JENUH SEBAGIAN DALAM ANALISIS STABILITAS LERENG

Infiltration causes the soil condition changes, from unsaturated soil to saturated soil, so that matric suction increase until zero and become positive pore water pressure. Pore water pressure decreases normal stress and soil shear strength, so that safety factor of the slope is reduced. The aim of this research is analysis effect of infiltration to unsaturated soil parameters change as matric suction, degree of saturated, shear strength parameters and safety factor of the slope. The laboratory test of matric suction uses filter paper method. This results are fitting soil water characteristic curve parameters with SoilVision program. Hydraulic conductivity function analysis uses Brooks and Corey�s equation (1964). Rainfall intensity analysis uses WindRose program and is obtained dominant rainfall duration. This results are used for rainfall models in infiltration analysis with modified Green Ampt infiltration method. Pore water pressure change analysis uses SEEP/W program and is used as parameters in shear strength parameters change analysis in slope stability analysis uses SLOPE/W program. Infiltration analysis indicates that the highest cumulative infiltration is caused by rainfall model III, namely average rainfall with longtime duration, meanwhile, average rainfall and high intensity rainfall in same duration (rainfall model I and rainfall model II) cause cumulative infiltration that relative similar. The pore water pressure change are significantly in initial rain season. The critic condition of the slope reaches if intensity rainfall 40 mm/day occurs during 15 days in October