Bulletin of the Geological Society of Malaysia, Volume 19, April 1986, pp. 613 – 625
1Lignite Mine Department, EGAT, Bangkok
2Department of Geology, Chulalongkorn University, Bangkok
3Department of Physics, Kasetsart University, Bangkok
Abstract: Landslides and slope failures have been recorded at the Mae Moh Lignite mine, Lampang Province, northern Thailand. These failures were found to be of three principle types, namely rock slides, topple rotational slumps and debris flows.
Field and laboratory investigations were carried out to analyse the stability of the present pit slope which comprises mainly of weathered claystones with thin lignite interlayers. The slope stability analyses were performed using the stereographical techniques of Hendron et al. (1971), Markland (1972), Hoek and Bray‘s (1974) stability chart method, and Bishop‘s (1955) simplified method of slices for the northwestern slope, and the back-analysis method for the southeastern slope.
Results of analyses indicate that slope instability is controlled by some or all of the following factors; (1) the bedding plane, the pre-existing fractures and their concurrent orientation to that of the pit slopes, (2) the geometry of the overall slope and the inclination of the individual benches, (3) the water seepage in the rainy seasons, (4) the degree of weathering and other engineering properties of the rocks.