Factors affecting debris mobility of open hillslope failures

Abstract

As a result of Hong Kong’s continual urban expansion, more infrastructures and buildings are developing closer to the steep natural hillsides. The risk of natural terrain landslides posed to these developments is of particular concern to the Hong Kong SAR Government. To safeguard life and property, a systematic study of natural terrain and implementation of any necessary hazard mitigation works has become a significant part of the Landslip Prevention and Mitigation Programme since 2010. A better understanding about the mechanism governing debris mobility of landslides is crucial to predicting the debris travel distance and the associated impact energy. This study is aimed at gaining a better understanding of the challenge behind assessment of debris mobility of open hillslope failures through reviewing the state of knowledge about their failure and mobility mechanisms, and investigating some key controlling factors that may have an effect on the apparent friction angles between the debris and the underlying materials. The study has examined 22 well documented open hillslope failures and back analysed them to obtain their apparent friction angles. The correlations between the apparent friction angles and the key controlling factors, such as source volume, slope angle, material properties of the debris, terrain setting and rainfall intensity, are examined in order to understand their possible effects on debris mobility of open hillslope failures. The scattering of data as revealed from the correlations has hampered the ability to draw firm conclusions about their relationship. Nevertheless, the results show that the key factors investigated could have some effect on the apparent friction angles and hence the debris mobility. Further study is recommended when more well documented cases of open hillslope failure and better data quality have become available.