Landslide induced gravitative debris flow in natural terrain

A gravitative debris flow is formed by an initial landslide that turns into a debris flow. During a wet season, the water content in the loose material at high elevation in a sloping terrain causes the material to decrease in strength such that an initial slide occurs. As the landslide mass slides down the valley, it experiences mechanical disturbance that leads to softening or liquefaction of the material. Consequently, further downslope movement of the softened or liquefied material is characterized with high mobility known as a debris flow. The high mobility leads to large runout distance over which destruction will occur.; The study in this thesis consists of two case studies of landslides in natural slope. The first landslide transformed into a debris flow while the second one did not. Several numerical models (Slope/W, FLAC, DAN and FLO-2D) have been applied for the analysis of these case records. Based on the findings of the case records, a parametric study has been conducted to investigate the effects of the soil parameters and the natural terrain inclination on the runout distance of a debris flow. The study leads to the following conclusions. (1) The friction model of the dynamic analysis of Hungr (1995) gives the most satisfactory result for this type of debris flow. (2) The runout distance increases with the decrease of the angle of friction mobilized after the initial landslide or with the increase in the natural terrain inclination. (3) The results of the parametric study have been compared to the observed runout distance of 28 debris flows and reasonable agreement has been obtained.