MEDIA TEKNIK SIPIL/JULI 2008/67 HYDROLOGICAL CONDITION LEADING TO LANDSLIDE INITIATION

The development of a physically based warning system for rainfall-induced landslides requires a comprehensive understanding of the hydrological condition leading to landslide initiation. The objectives of this research were to evaluate and document the hydrological response of a potential landslide area to heavy rainfall and to assess the significance of the antecedent soil moisture condition to landslide initiation in volcanic residual soils. A field site in an area of previously landslide activity was instrumented and monitored during rainfall period using a number of jet-fill tensiometers. Field monitoring of pore-water pressures indicated that the hydrological response of the soils was spatially and temporally varied in depth. Generally, pore-water pressures within the slopes decrease as the depth increases. At the greater depth, a preferential path for moisture movement may exist to contribute the generation of pore-water pressures. Based on this field measurement, the numerical analyses show that dry antecedent soil moisture condition will require rainfall of high intensity to saturate the soil profile and to disturb the stability of the slope. Under wet antecedent soil moisture condition, rainfall of 80 mm/day is likely to produce the hydrologic condition leading to landslide initiation