The 28 July 2015 rapid landslide at Ha Long City, Quang Ninh, Vietnam

From 26-28 July, heavy rainfall occurred in Quang Ninh province causing flooding, debris flows and landslides. It was the largest disaster triggered by torrential rainfall in Vietnam in 2015. The immediate economic loss in Quang Ninh is estimated to be about VND 2000 billion (US$92 million). Seventeen people were reported dead, 1,459 households were evacuated and at least 30 houses were destroyed. Eight of the victims died when a landslide buried three houses at Cao Thang ward, Ha Long City. We undertook field investigation and ring-shear simulations to study the initiation mechanism and behaviour of the landslide. The rainfall-induced pore-water pressures were estimated using the Slope-Infiltration-Distributed Equilibrium (SLIDE) model developed by Sassa et al. (2010) and Liao et al. (2010, 2012). The ring-shear apparatus (ICL-1) was used to simulate the soil failure, formation of sliding surface and steady-state motion of the landslide. Landslide dynamic parameters obtained and estimated from ring-shear tests were used in the integrated simulation model LS-RAPID to simulate landslide motion. The results demonstrate that the LS-RAPID model predicts a similar hazard area to that observed in the field investigation. In addition, the time of landslide occurrence estimated from the rainfall record and the LS-RAPID simulation is close to the time of occurrence reported by local inhabitants.