This paper presents a case study of a major landslide that occurred during the construction of a national expressway in Chongqing, southwestern China. The landslide was a typical plane failure associated with steep cutting in weathered mudstone and sandstone. The weathered mudstone block slipped down along the bedding interface of the mudstone and sandstone and formed an open gap that measured some 6 to 8 m high, by 2 to 7 m wide and 53 m long in the hillside slope. This study referred that the landslide was caused by the combined effect of the following factors: (a) an unsupported high and steep cutting in weathered mudstone; (b) an exposed bedding interface between the incompetent weathered mudstone and the competent sandstone that daylights within the cut slope; (c) the mudstone and sandstone bedding interface as a pre-existing folding tectonic shear plane of low shear strength; and (d) the possible presence of a ground water table in the weathered mudstone perched on the relative impervious sandstone bedding surface. The case study highlights the importance of engineering geologicalmapping during and immediately after the formation of a new cut slope. It also emphasises the importance of identification of the pre-existing tectonic shear planes along the mudstone and sandstone bedding interfaces in similar geological terrain.

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