Rainfall Induced Rock-Fall Debris Avalanche in October 2010, at Kwande Local Government Area of Benue State, Nigeria

Abstract

Abstract This study explains the causes and the mechanism of the landslide occurrence at Kwande local Government Area of Benue, Nigeria in 2010. Although there was no fatality or any damage in the area, a large area of farmland was destroyed, trees were uprooted and a normal stream course was also disturbed. To study and understand the landslide event, a combination of geotechnical investigations and statistical data were used. These parameters were applied to a numerical model to simulate the causes of the landslide. Results of the geotechnical investigations made on samples taken from the area, showed average maximum dry density value of 1.6kg/m3, and average optimum moisture content value of 14%, hence the low to moderate density is indicative of a soil that can easily disperse. Also the triaxial compression test showed an angle of internal friction and cohesion values averaging around 14.82° and 25kPa respectively, and these low values indicate that the shear strength of the soil was reduced, due to the combined effect of increase in slope gradient, and high precipitation intensity which increased to a monthly value of 145mm before the landslide. The simulation result showed that the factor of safety value was 1.158, which is still close to the value for an incipient failure. Hence the results shown can be used in predicting the mechanisms and areas of possible landslides, as well as the causes of such soil deformations, and as such, safety measures could be taken against the reoccurrence of landslides in the area.