5 October 2020
The Jimei landslide: inducing reactivation of an ancient failure through tunneling
It is well-established that poorly planned or inappropriate tunneling can induce landslides. This is particularly the case when the tunnel penetrates an ancient landslide, which most frequently occurs because the features of the existing but dormant mass movement were not identified at the ground investigation stage. Once movement is initiated it is difficult and expensive to re-establish stability.
In a new paper in the Arabian Journal of Geosciences, Wang et al. (2020) describe the impact of a twin bore tunnel on an ancient landslide in Gulin County in Sichuan Province, China. The tunnels were bored as part of a highway construction project. They penetrated the two lobes of the ancient Jimie landslide, which was reactivated as a consequence.
The image below, from Google Earth, shows the site, located at 28.059, 105.676. The image is from 2019, so post-dates the mitigation of the problems.
The paper suggests that these features were identified as landslides prior to construction, and that the aim had been to locate the tunnels in bedrock below the shear surface. However, the tunnel appears to have penetrated the landslide mass, inducing reactivation, which caused serious deformation in one of the tunnels. Note that, as the image above shows, the landslide is occupied by houses and a school, so reactivation has significant implications.
Wang et al. (2020) provide the following cross-section in the paper. This is a large slope failure – 11 million cubic metres in volume and up to about 73 m in depth:
The paper goes on to simulate the effects of mitigating the landslide through removal of a portion of the upper part of the landslide to reduce the driving force. The paper simulates the excavation of 1.3 million cubic metres.
Perhaps surprisingly the paper does not really describe what was actually undertaken at this site, but the Google Earth image appears to show that a substantial portion of the landslide was removed. The 2019 Google Earth image shows traffic on the road, so it appears that the mitigation was successful.
Quickslide 1: the impact of landslides in India
Quickslide 2: Landslides and floods in France, Italy, Switzerland and the UK
Wang, Z.F., Shi, F.G., Li, D.D. et al. 2020. Tunneling-induced deep-seated landslides: a case study in Gulin County, Sichuan, China. Arabian Journal of Geosciences 13, 1039. https://doi.org/10.1007/s12517-020-06048-5