Previous researches regarding landslide in Thailand have focused mainly to classify landslide hazard areas based on the analysis data in various factors such as topography, land-use, slope angle of soil slope, rainfall intensity etc. The field investigation and this research are aimed to geological setting, engineering properties of residual soil from parent rock including physical properties, properties of the soil shear strength decreases when the moisture content increases. In the study area, Ban Nong Pla, Amphoe Chiang Klang, Changwat Nan, found clastic sedimentary rocks are a parent rock including shale, sandstone, and siltstone. These residual soil and weathered rocks have a rate of high weathering therefore resulting to high susceptibility for landslide. As a result, the average value moisture content of soil, the average value specific gravity of soil, the average value liquid limit, and plastic limit are 24.83 %, 2.68, 44.93 % and 29.35 %, respectively. Plastic index is 15.58 % .Permeability value of soil is between as 9.36E-06 - 6.81E-07 cm/sec, respectively. Soils in the study area are classified by Unified Soil Classification System including ML- CL, CL- ML, ML- OL, SC and SM. The cohesion of soil values ranges from 0.096 to 1.196 ksc and angle of internal friction is between 11.51 - 35.78 degrees, respectively. Based on three resistivity lines survey, thickness of soil is between 2-9 m depth. The thickness of soil overlying on rock basement is important for calculating the volumetric of possible collapse. In conclusion, the result show that the failure slopes are greater than or equal 25 degrees, where soil profiles are overlying on the weathered clastic sedimentary rocks with high natural water contents. The change of factor of safety will occur where the soil depth between 2-5 m is located close to the depth of the actual slide zone.

Thesis (M.Sc.)--Chulalongkorn University, 2012