The catastrophic landfill flowslide at Hongao dumpsite on 20 December 2015 in Shenzhen, China

Abstract. A catastrophic flowslide occurred at the Hongao dumpsite on 20 December 2015 in the Guangming New District of Shenzhen, China. The flowslide caused 77 causalities and damaged 33 buildings. In the absence of extreme weather conditions and seismic activity, the causes of the failure were analyzed on the basis of multi-temporal remote-sensing images, site investigation, in situ tests, laboratory tests, and numerical analyses. Site investigations showed that the volume of the displaced material was 2.32  ×  10 6 m 3 and the volume of the pre-failure waste filling was 6.27  ×  10 6 m 3 . The flowslide was characterized by high travel velocity and long runout distance. The displaced material was primarily a mixture of silty soil and construction and demolition waste with water content of 17.3–42.4 %. The primary causes of the failure were concluded to be the following: (1) groundwater flow had stagnated in the dumpsite due to drainage system failure and the underlying impermeable granite stratum; (2) the accumulation rate and total volume of the waste filling was in exceedance of the design capacity. The flowslide may be ascribed to the development of excess pore-water pressure as evidence of liquefaction was observed at several locations, and it is postulated that such phenomena were related to the surcharge loads imposed by the unregulated disposal activities.