Landslide mobility factors at Tsing Shan area

Abstract

A study of landslide mobility factors has been carried out at the Tsing Shan Foothills area, Tuen Mun in an area where a significant number of natural terrain landslides have occurred over the past few decades, most notably a large individual landslides in 1990 and a swarm of 118 landslides in the year 2000. Some of the landslide travelled down to existing facilities and caused impact to development.

The main objective of the study was to review and correlate the key landslide properties such as source volume, slope angle, debris travel distance, angle of reach, deposition rate and analyse their influence on landslide mobility for open hillslope landslides at the Tsing Shan area. The study will also examine the effect of source material type, in terms of constituent particle size, as one of the potential factors influencing landslide mobility. Thus, the study will attempt to refine the prediction of landslide mobility based on material type, which may have an impact on the design of appropriate landslip mitigation measures for open hillslope landslides.

Data has been obtained from the 118 nos. of landslide mapping reports carried out between February 2001 and July 2001 by Maunsell/Fugro JV. Other parties studied some landslides that occurred within the study area during the April 2000 landslide swarm. These include Halcrow China Limited who studied four selected landslides, in the Leung King area, and GEO who studied the large 1990 debris flow.

The data for analysis is presented in the form of tables together with series of plots which have been interpreted and discussed in terms of trends and behaviour of different landslide material types related to other landslide characteristics.

From the study, it is concluded that apart from the typical key landslide properties, material properties of the landslide source will also have some influence on the landslide movement type and affect mobility of open hillslope landslides. By studying landslide source material types over the study area, and relating them to the mobility and underlying geology, we can relate certain material types to local geology so that the findings could be applicable elsewhere.