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Dr. Xu Chong joined a national earthquake rescue team and went to Zhongxing Town, Dujiangyan to carry out disaster rescue of the “2013-7-10” landslide type debris flow at Sanxi Village

2014/5/27 9:59:13

Affected by 38 hours’ strong rainfall, a large disastrous “landslide type debris flow” happened at Wulipo, Sanxi Village, Zhongxing Town, Dujiangyan City after 10 am July 10, 2013 (103°33′49"E, 30°54′55″N). By July 14, it was confirmed that tens of people were killed and more than 100 people were missing or buried by the debris flow. The national earthquake disaster emergency rescue team was ordered to support the disaster rescue work in the disaster area on July 13. The team was led by Deputy Director Yin Guanghui.

Dr. Xu Chong has been engaged in landslide research all the time. From this field study, he preliminarily obtained the following information: (1) The landslide in this landslide type debris flow happened at a high slope position, its potential energy is large and its rear margin is almost at the top of the slope. (2) The initial sliding distance of the landslide mass is short, but due to heavy rain, the landslide substances were softened and pore water pressure increased. As a result, some loose landslide substances were converted in a short time into a debris flow at a high moving speed and rushed to the mouth of the gulley. The horizontal movement distance is about 800m. The debris flow destroyed some residential houses on the way and caused huge damage. (3) Although a large amount of soil and stones has been converted into a debris flow and caused enormous damage, there is still a large amount of loose substances on the landslide mass, which are very likely to slide again and become another debris flow in the future in case of heavy rain.  

The reasons for this landslide type debris flow are as follows. (1) Long lasting strong rainfall: The accumulated rainfall in Dujiangyan within 38 hours before occurrence of the disaster was 920mm. Such heavy rainfall not only softened slope structure but also formed tremendous pore water pressure in slope fissures. The water that was not discharged in time was mixed with landslide substances to form rich sources of debris flow, which was easy to induce a debris flow disaster. (2) Influence of the 2008 Wenchuan earthquake: It is unknown whether fissures had been generated at the rear margin of this landslide during the Wenchuan earthquake because the landslide has happened and the current fissures on the rear wall of the landslide probably was formed by this slide. Anyhow, the area of this landslide experienced violent vibration during Wenchuan earthquake. Inevitably the structural integrity and strength of the slope was undermined to some extent. (3) Steep terrain: The terrain in the occurrence position of the landslide is steep and has a free face for development of a large landslide. (4) Influence of lithology: The lithology of the landslide occurrence area is relatively weak Jurassic and Cretaceous sandstone, which is prone to softening under the action of rainwater.

Fig. 1  Material rushing out of the debris flow gulley blocks the highway

Fig. 2  Accumulation area of landslide-type debris flow

Fig. 3  Accumulation of the debris flow went up to a path and is higher than car roof

Fig. 4  Search and rescue is ongoing

Fig. 5  Substances staying in landslide source area may continue to slide in case of strong rainfall

Fig. 6  The potential landslide hazard on Qingcheng Mountain is non-negligible