Experimental Modeling of Rainfall and Seismic Activities as Landslide Triggers

Abstract

A series of experiments were conducted on loose sand, in order to determine the relationship between void ratio, intensity and duration of rainfall, and slope stability. A soil sample was placed into a Plexiglas container at the void ratio of 0.7 to make a 56 cm. thick model and then cut into a slope at different angles to introduce targeted rainfall with a rain simulation system in order to measure the seepage rate, moisture content, degree of saturation, soil settlement, and surface erosion with time. The degree of saturation in the soil mass decreased with depth from the top surface after the termination of rainfall. However, this reduction in degree of saturation from top to bottom of the slope is less in steeper slopes. Following the rainfall experiments another series of experiments were conducted to determine the relationship between void ratio, seismic acceleration, and slope stability. The soil sample was placed into the same container and compacted to the desired void ratio to form the same 56 cm thick model. Two accelerometers were then placed, each at 12 cm. and 36 cm. heights from the base of the model to measure the amplification of seismic acceleration at different depths. The soil sample was cut into different slopes and shaken with different accelerations for multiple cycles until the slope failed. Similar experiments were conducted for soil samples compacted at four different void ratios. The experimental result shows that the seismic acceleration amplified with the increase in vertical distance from the base of the model and also with the reduction in void ratio. BACKGROUND Landslides are ground movements that occur when the stability of a slope becomes unstable due to various reasons. Slope stability represents an important widespread hazard, occurring all over the world including the United States. Landslides cause $1-2 billion dollars in damages and more than 25 fatalities on average each year (USGS webpage). The desire to obtain the perfect view and the increase in population of the coastal area and hillsides contribute to an increase in man-made landslides. Coupled with natural hazards, such as earthquakes, rainfall, erosion, and the transitional changes between the levels of the water table landslide hazards are making our slopes unsafe. The ideal course of action is to reduce damages and fatalities by better understanding slope stability. Although many