GIS-Based Landslide Susceptibility Map Verification by its Geotechnical and Geological Characteristics

Abstract

The famous 2006 Laplae rainfall-triggered landslide has caused hundreds of million Baht lost. The objective of this paper is to evaluate and to compare present geotechnical and geological conditions between the landslide area and landslide-free area to verify a landslide susceptibility map. Detailed field surveys acquired 14 samples: undisturbed, disturbed soils as well as rocks. Sensitivity and back-analysis were also performed. 35.44% of landslides occurred in meta-shale - greywacke-interbedding Formation, and another 64.56% happened in meta-greywacke - basaltic andesite Formation. The dominant slope of the landslide is in 30⁰-40⁰ slope, with aspects toward South direction, and in a range of <1,000 meters from geological structures. Landslide area is distinguished from the non-landslide area by its various grades of materials, lower quartz content, higher clay content, finer composition of parental rocks and soils, higher average ratio of smectite versus quartz, lower compressive strength, lower shear strength, lower angle of internal friction, lower cohesion value, more poorly graded, higher soil moisture, higher liquid limit and plasticity index, and factor of safety is generally less than 1. The result of the sensitivity analysis indicated that in a failure condition, the cohesion and angle of internal friction angle values are equal to 2.51 kPa and 13.70⁰, respectively. However, the results of laboratory tests showed that the cohesion and angle of internal friction values are equal to 8.59 kPa and 14.2⁰. These results verified the landslide susceptibility map that the high landslide susceptibility area has the engineering characteristics of the landslide-prone area, while the low susceptible one has the characteristics of the non-landslide area.