Influence of Soil Physical Properties, Soil Parent Materials and Precipitation on Landslide Occurrences in Thailand

Orathai Sukreeyapongse, Pramuanpong Sindhusen, Somjai Chenyapanich and  Hathairat Pichainarong Abstract Soil properties of major landslides that occurred on slope complexes in Thailand were analyzed. The character of the parent material plays an important role in determining soil properties. Representative five soil profiles including granite derived soils in Nakonsrithammarat province (KT and KWg soils) and fine grained clastic rock and shale derived soils in Phetchabun (PNg and NK soils) and Uttraradit provinces (NT soil) were studied. On a granite landscape, KT and Kwg soils have a relatively coarse texture (sandy loam to sandy clay loam). Field capacity (FC) of KT and Kwg soils ranges from 17-33%wt. The hydraulic conductivity (Ksat) of KT and Kwg soils values ranges from 11-79 cm hr-1. While in the hillslope derived from fine grained clastic rock and shale, PNg, NK and NT soils have clayey texture. FC of PNg, NK and NT soils ranges from 29-39%wt with Ksat ranging from 0.14-104 cm hr-1. The nature of the parent material and the rate of parent material weathering can greatly affect hydrological and erosion processes. The differentiation of Ksat, especially at the lower limit of the clayey texture soils caused the landslide occurrence. Climatic conditions are characterized by a mean annual precipitation at Nakonsrithammarat province of 1,640 mm in November 1988 and a mean annual precipitation at Phetchabun province of 157 mm in August 2001 appeared to be sufficient to cause landsliding.

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