Flowslide on a fill slope triggered by a burst water pipe: a case history

This paper presents a case study in Hong Kong of a flowslide occurred on a fill slope triggered by a burst water pipe buried near the slope crest. The onset of failure was recorded by nearby pedestrians and the video was immediately posted in social media, which had caught noticeable public attention. The flowslide resulted in a temporary closure of an undermined road section at the slope crest. The debris travelled over 500 m down the natural hillside within a country park. No casualties were reported. History of the site was studied. Information was collected to establish the chronological order of events happened before the flowslide. Post-landslide investigations including field mapping in the source area and along the debris trail, ground investigations, and a fluid-coupled numerical study were undertaken to examine the probable cause and mechanism of the failure. It is diagnosed that the high mobility of this landslide would be caused by the saturation of a loose fill layer in the slope due to water egress from the burst pipe, which in turn might have triggered a static liquefaction of the loose fill. Lessons learnt from this case history and measures to minimize similar landslide hazard on other fill slopes with similar settings are discussed.