Engineering Information for a Study on the Landsliding Susceptibility of the Banaue Viewpoint Rice Terraces and Maligcong Rice Terraces

摘要

Information and data that can be useful for an engineering study for the conservation of the Rice Terraces in the Philippine Cordilleras are collated. Presented here are the rice terraces in Barangay Viewpoint in Banaue, Ifugao and in Barangay Maligcong in Bontoc, Mt. Province. Photographs taken in a recent site visit (August 2002) are shown to illustrate the topographic settings of these two terraces. Information on the geologic setting, geotechnical engineering aspects, and construction of these terraces is presented. Photographs of recent landslides taken in the visit are also shown and the possible mechanisms, approximate sizes and the soil mass movement of these landslides are also describe i and illustrated. Considering that these landslides coincided with the harvest season at these terraces, when most of the soils are unsat-urated, a possible mechanism of these landslides is correlated to the shearing behavior of unsaturated soils. Noted is the reduction of soil suction, which contributes to the shear resistance to landsliding, induced by heavy rains. As the terraces are subjected to an agricultural cycle of wetting and drying, it is further noted that a study on the soil-water hysteresis phenomenon in soils in the terraces can be pursued as a potential landslide mitigation measure.