29 July 2020
The Niushou landslide in Jiangsu Province, China
The journal Landslides has an article (Li et al. 2020) in its Recent Landslides section describing the interesting Niushou landslide, located in a tourist area in the region administered by Nanjing City in Jiangsu Province, China. This is located at 31.912, 118.740. This is the site as depicted in Google Earth:-
Niushou Mountain is an important cultural area, home to over 30 Buddhist temples. To accommodate visitors, a project was initiated, as the works in the image above show, to construct a hotel for the Atila group. This was a large project, including 29 villas as well as the main hotel complex, over an area of about 24,000 m2. The image, from Li et al. (2020), below shows the site in June 2016 – the image is taken looking downslope:
Li et al. (2020) report that after construction of the hotel began, a tension crack developed upslope of the hotel in June 2015 (marked in red on the image above). I assume, although this is not explicitly described in the article, that the slope had been cut to create the platforms for the hotel complex. Movement developed during heavy rainfall.
From summer 2015 to March 2016 efforts were made to stabilise the site with piles, anchor cables and drainage. However, on 11 June 2016 the slope failed during a further period of heavy rainfall, although the rate of displacement was low. Monitoring data indicates that the landslide has continued to move in periods of heavy rainfall.
Li et al. (2020) present a detailed investigation of the landslide, which has a volume of about 4 million cubic metres. It’s about 170 metres long and 105 metres wide with a maximum depth of 26.3 metres. Movement occurs on a weathered tuff layer with a mean slip surface gradient of about 10 to 12°. The paper does not describe whether this was a pre-existing area of instability (i.e. a relict landslide), but my interpretation of the morphology of the site suggests that this could be the case.
It is clear that the excavations for the hotel project activated (or reactivated) the slope, which failed when groundwater levels were high. Li et al. (2020) note that the 2016 rainfall event was unprecedented – it is likely that we are seeing the combination of design issues and increased rainfall from global heating.
As a consequence of the Nuishou landslide the hotel project has been abandoned, with a direct economic cost of 30 million RMB (US$4.3 million) and a potential total economic cost of up to 150 million RMB (US$21.5 million).
Quickslide 1: landslide costs in Nepal continue to mount
There are various reports this morning of further fatal landslides in Nepal, including up to ten fatalities in Rukum and Kalikot.
Quickslide 2: landslides along the Istanbul Canal
The Istanbul Canal is a proposed waterway between the Black Sea and the Sea of Marmara. A recent study has identified 267 landslide zones along the alignment.
Li, Z., Zhang, F., Gu, W. et al. 2020. The Niushou landslide in Nanjing City, Jiangsu Province of China: a slow-moving landslide triggered by rainfall. Landslides (2020). https://doi-org.sheffield.idm.oclc.org/10.1007/s10346-020-01441-3