Abstract

Tropical residual soil has unique characteristics due to the influence of weather. The intensity of the rainfall is much high, and landslide become a serious threat. The number of landslides in West Java is numerous, more than 100 events yearly. Landslide is produced if the unsaturated zone on the upper side of a slope becomes saturated, hence it is necessary to characterize the unsaturated zone phrone to landslide on a slope. Three location of tests were selected, i.e. Cijengkol Slope, Neglajaya Slope and Kalijati. A research of weathering zone on residual soil were conducted with Scan Electron Microscopy (SEM) and X-Ray Diffraction (XRD) methods to gain the physical and geo-chemical characteristic of slopes, then a suction measurement of Filter Paper Method were conducted. This resulted in a conclusion that the weathering zone is a major reason to define the depth of unsaturated zone. A zone called zone 4 (the term from Little,1969) is defined as a zone where weathering process change between disintegration of base rock to lateritation process. The profile above zone 4 is a zone where unsaturated zone highly influenced by weather and potential to slide. A series of in-situ tests (CPT-u and Dilatometer Test) and drilling for SPT and undisturbed samples and laboratory tests were conducted to confirm the characteristic of this zone. The in-situ test were proved to be effective to define and characterize this zone, and consequently proved to be successful to define the unsaturated zone for landslide analysis. © 2011 Taylor & Francis Group, London.