Scarp morphology and development associated with a large retrogressive compound landslide at Lai Ping Road – Hong Kong

This paper briefly describes morphology and interpretations of scarps associated with a large, slow moving, retrogressive, compound landslide that affected a cut slope at Lai Ping Road, near Sha Tin, in the northeast of Hong Kong. The cut slope failed after intense rainfall on 2 July 1997, and five landslides occurred, with a combined volume of 4000 m3. The relatively mobile debris impacted with a covered service reservoir but no major damage resulted. Surface ground deformation extends 50 m into the quasi-natural terrain above the cut slope. This is bounded by a main scarp, up to 4 m high, which indicates the presence of a failed mass whose volume is estimated to be up to 100,000 m3. Surface mapping has revealed numerous scarps and tension cracks, within the confines of the main scarp. These scarps are of differing ages and structural morphotypes, including horsts, grabens, en echelon arrays and duplexes. The scarps and tension cracks were influenced in their development by the relict joint structure, depth of weathering and hydrogeology of the slope. It is concluded that the slope has had a lengthy history of spasmodic, deep seated deformation dating back to the initial formation of the cut slope in 1978.