Analysis of a Deep-Seated Landslide in the Phan Me Coal Mining Dump Site, Thai Nguyen Province, Vietnam

Abstract

A large landslide occurred at the Pha Me coal mining dump site at 4:20 AM on 15 April 2012, buried a huge area, including tens of houses and seven persons. There was no abnormal weather or seismic activity at the time of the landslide. A joint work between Vietnamese and Japanese experts was carried out to investigate characteristics and reasons of the landslide. The achieved results show that coal mining wastes are disposed of on low hill sites where granitic bedrock was intensively crushed due to tectonic activity. Weathering crusts include rich clays of over 15-20 m in thickness. The landslide has a volume of about 2.5 million m3, with a slip surface cut through weathering soils at a depth of about 10 m. The scarp of the landslide departs at an approximate elevation of 85-100 m. Travel distance is 300-350 m. Sliding materials are primarily mining wastes. However the sliding surface is defined to be situated at the depth of 12-15 m in the residual soils. There are two significant causes of the disaster. Firstly, the waste dump site plays a role as a water-storage layer which keeps residual soils permanently saturated. The second cause of the deep-seated landslide is over-loading of mining wastes. Prior evidences of the landslide such as cracks at the top, heave at the trough of the dump site were recognized a week before, however they were not seriously considered.