Study on Landslides in Weathered Granite Areas of Hai Van Mountain, Vietnam

Abstract

Located in the Central Region of Vietnam, Hai Van Mountain is one of the highest risk areas prone to landslides that threaten frequently to safe traffic operations of the national transport systems. This area suffered to several serious damages caused by slope failures to infrastructures and environment in the past. This study presents some results obtained by site observations and the use of ring shear apparatus to investigate the failure mechanism of slopes in weathered granite areas of Hai Van Mountain. The most common types of the landslide in Hai Van Mountain including earth slides, rock falls, and debris flows were found through site investigations. Among them, sliding types are characterized by a complex form of rotational and/or translational modes. Shallow landslides were frequently induced by rainfalls due to loose and unconsolidated materials of slopes. Specifically, the physically landslide mechanism was examined on with two different weathered granite samples taken in the study area by using un-drained ring shear apparatus. The laboratory experiments revealed that only less/moderate weathered granitic soil samples (HV2 sample) were susceptible to a high mobility and experienced liquefaction behavior at sliding surface. In contrast, strongly weathered granite samples (HV1 sample) did not show those features under undrained shear stress loading conditions. The results implied that landslides of weakly weathered granite materials are highly susceptible to rapid motion while the strongly weathered granite materials is not apt to move at the high speed. Another key point, less weathered granite materials are more vulnerable to rainfall-induced landslides because its shear resistance strength was weaker than that of heavy weathered granites under the rainfall impact (Tien et al., 2015). This significant finding was agreed with the evidence and the results from site observations.