A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Geotechnical and Earth Resources Engineering

Thesis (M. Eng.) - Asian Institute of Technology, 2023

In landslide and debris flow research, many practices have been developed and applied to evaluate their characteristics and mechanisms for a better assessment. Geotechnical investigation is one of the valuable approaches that could contribute to a better understanding of debris flow behavior. Khlong Narai Debris Flow is a hazard that occurred in April 2017. This study area is located in Chanthaburi, Thailand. It is a granitic-related debris flow that was considered susceptible to landslides and debris flow according to various research. The field investigation and laboratory testing of the study area resulted in high-plasticity soil with low hydraulic conductivity. The application of slope stability analysis, empirical equations, and numerical simulation is involved in this study to estimate the thickness, volume, and behavior of debris flow. The thickness of possible failure derived from DEMs, and empirical equation based on slope gradient and elevation ranged between 0.25-20.76m., which resulted in an average failure volume of about 30,000 m3. The slope stability analysis could simulate the failure scar according to the boundary condition and parameters provided to the model. The results revealed that was not only precipitation causing the debris flow in this area, but there was a combination of another possible source of water from water pipe leakage (scope of the study). The characteristics and behavior of Khlong Narai Debris Flow were simulated using a 2D-runout model named RAMMS. The calibration gave appropriate Voellmy fluid-friction parameters for Dry-Coulomb friction ({uF06D}) and Viscous-turbulent friction (q) are 0.4 and 200 respectively with a yield stress value of about 100kPa. This sensitivity analysis allowed us to estimate the velocity of the flow at about 16.62m/s.