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Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
In general, the June 2008 landslide debris was found to be
more mobile when compared with the previous historical
natural terrain landslides in Hong Kong (Figure 6). About
20% of the June 2008 landslides have runout distances over
100 m, as compared with about 10% in past landslides that are
observed from old aerial photographs.
Detailed studies on selected CDFs revealed that some of
the CDFs with long runout generally involved debris with
high water content, e.g. the failure near Yu Tung Road
(Figure 5). After detaching from the source of failure, the
debris mixes with a large amount of water along the drainage
line, and results in higher debris mobility. LI revealed that a
number of circumstances may lead to such ‘watery debris’,
such as:
(a) debris flows along a major drainage line with a large
catchment and a long flow path;
(b) debris flows occurring during heavy rain; and
(c) debris flows along a main drainage line into which many
tributaries of drainage lines are feeding.
To facilitate the modeling of debris mobility under such
circumstances for natural terrain hazard studies, systematic
back analyses were carried out on some selected long runout
CDFs that occurred in June 2008 using a 2-D dynamic
modelling algorithm, known as ‘debris mobility modeller’
(2d-DMM) program, as well as 3d-DMM in some cases, to
refine the modeling parameters. Improved guidance on debris
mobility modeling was promulgated by the GEO (2011).
9. CONCLUSIONS
The landslide investigations have brought insights into the
causes, mechanisms and characteristics of landslides. The
investigations enhance the understanding of the behaviour of
man-made slopes and natural hillside under severe rainstorm
and the findings have helped to advance geotechnical
engineering practices, and improve standards and design
guidelines for enhancing the robustness of slope upgrading
and landslide mitigation works.
ACKNOWLEDGEMENTS
This paper is published with the permission of the Head of the
Geotechnical Engineering Office and the Director of Civil
Engineering and Development, Government of the Hong
Kong Special Administrative Region.
REFERENCE
AECOM Asia Co. Ltd. (2009) “Detailed Study of the 7 June
2008 Landslides on the Hillside above Yu Tung Road,
Tung Chung” (GEO LSR No. 14/2009). GEO, CEDD,
Hong Kong.
Figure 5: Yu Tung Road channelized debris flow
ETWB (2006). “Code of Practice on Monitoring and
Maintenance of Water Carrying Services Affecting Slopes
(Second Edition)”. Environment, Transport and Works
Bureau, Hong Kong.
Fugro Scott Wilson Joint Venture (2008). “Review of Sub-
surface Drainage Provisions for Recompacted Fill Slopes”
(GEO Report No. 225). GEO, CEDD, Hong Kong.
GCO (1984). “Geotechnical Manual for Slopes” Geotechnical
Control Office, Civil Engineering Services Department,
Hong Kong.
GEO (2004a). “Guidelines for Assessment of Old Masonry
Retaining Walls in Geotechnical Studies and for Action to
be Taken on Private Walls” (GEO Circular No. 33). GEO,
CEDD, Hong Kong.
GEO (2004b). “Fill Slope Recompaction – Investigation,
Design and Construction Considerations” (GEO
Technical Guidance Note No. 7). GEO, CEDD, Hong
Kong.
GEO (2008). “Guide to Soil Nail Design and Construction”
(Geoguide 7). GEO, CEDD, Hong Kong.
GEO (2009). “Enhancement of Rock Slope Engineering
Practice Based on Findings of Landslide Studies” (GEO
Technical Guidance Note No. 10). GEO, CEDD, Hong
Kong.
Figure 6: Distribution of landslide runout distance
GEO (2011). “Guidelines on the Assessment of Debris
Mobility for Channelised Debris Flows” (GEO Technical
Guidance Note No. 29). GEO, CEDD, Hong Kong.
Hui T.H.H., Sun H.W. & Ho K.K.S. (2007). “Review of
Slope Surface Drainage with reference to Landslide
Studies and Current Practice” (GEO Report No. 210).
GEO, CEDD, Hong Kong.
Maunsell Geotechnical Services Limited (2009). “Detailed
Study on the 7 June 2008 Landslide on the Natural
Hillside behind Chow Yei Ching Building at the
University of Hong Kong” (GEO LSR No. 3/2009). GEO,
CEDD, Hong Kong.
Morgenstern N.R. & GEO (2000). “Report on the Kwun Lung
Lau Landslide of 23 July 1994” (GEO Report No. 103).
GEO, CEDD, Hong Kong.
Wong H.N. (2003). “Natural terrain management criteria -
Hong Kong practice and experience.”
Proceedings of the
International Conference on Fast Slope Movements -
Prediction and Prevention for Risk Mitigation,
Naples,
Italy, vol. 2.
Wong H.N. (2009). “Rising to the challenges of natural
terrain landslides.”
Proceedings of the HKIE Annual
Seminar on Natural Hillsides: Study and Risk Mitigation
Measures
, HKIE, Hong Kong, 15-54.
