Report No. : GEO Report No. 239

Report Title : Detailed Study of the 22 August 2005 Landslide and Distress on the Natural Hillside at Kwun Yam Shan, below Tate's Ridge (2008), 138 p. plus 2 drgs.

Author : Maunsell Geotechnical Services Limited

Abstract

This report presents the findings of a detailed study of a landslide incident (Incident No. 2005/08/0422) that occurred on a natural hillside at Kwun Yam Shan, below Tate's Ridge. The landslide was reported in the early morning of 22 August 2005 following heavy rainfall on 19 and 20 August 2005. The landslide involved a total displaced volume of about 2,350 m³, much of which remained in the source area. About 1,000 m³ of material detached from the source and developed into a debris flow, which travelled a total distance of about 330 m down a drainage line, finally coming to rest within the drainage line. An approximately 10 m section of the MacLehose Trail was severed. No casualties were reported as a result of the landslide.

Significant signs of distress were subsequently identified on the hillside above the source area of the August 2005 landslide. Extensive tension cracks defined an area of distressed hillside within which relatively smaller scale tension cracks, collapse features and erosion gullies are present.

The key objectives of the study were to document the facts about the landslide and the distressed hillside, present relevant background information and establish the probable causes of the landslide and the observed distress. The scope of the study comprised desk study, site reconnaissance, detailed field mapping, engineering geological mapping, ground investigation and laboratory testing, together with theoretical analyses. Recommendations for follow-up actions are presented separately.

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