Reservoir-Scale Landslide Susceptibility Analysis of Slopes Surrounding Artificial Impoundments by Three-Dimensional (3D) Limit Equilibrium Models: A Case Study of San Pietro Dam, Avellino Province, Italy.

Landsliding problems in slopes surrounding reservoir lakes are sometimes induced or reactivated by  reservoir operation  activities (Xia et al., 2015). Regular landslide susceptibility assessments are essential for safeguarding lives, infrastructure, and the environment, this being highly amplified for reservoir basins. Landslide assessments are commonly done through heuristic, statistical and physically-based quantitative methods such as limit equilibrium (LE) analysis. However, quantitative LE analyses have been historically carried out in 2D and at single-slope scale due to the need of reducing computational requirements, although realistically slope failures are 3D in nature; hence, using 3D methods can likely yield more accurate results and is more suitable for the understanding of the landsliding processes. Nowadays, with increased computational capability, it is possible to move to more representative 3D approaches and even attempt to extend the scale of application not only for shallow landslides, but also deep and complex landsliding processes. Since most 3D LE analyses are performed at slope scale, this study aimed at moving from slope to reservoir basin scale to assess the overall susceptibility to slope failure at the San Pietro Dam. The adopted methodology used Slide3 Software and involved generation of study area's 3D geometry from a 10-m resolution DEM. Then, stratigraphic borehole data, along with stratigraphic sections obtained from geological reports for the area were used to reconstruct 3D geological schematization. Geotechnical strength parameters between residual and peak strength derived from literature were used as inputs for stability analysis. Specifically, 3D extension of the Morgenstern and Price method, which   divides the potential failure surface  into  columns based on Cheng & Yip (2007) formulation for asymmetrical slopes was used. Results indicate that the approach is able to provide distribution of potential areas susceptible to slope instability as safety factor (SF) values which were in good agreement with field observations and the landslide inventory map. In particular, many landslides fall in marginally stable pixels of the SF map and can reactivate depending on the increase of water table levels along the slopes. Effect of potential rapid drawdown of the reservoir level on the stability of surrounding slopes was also investigated. The results shed light on possible extension of 3D LEM to scales larger than a slope so that it can become a useful tool for landslide risk management in reservoir environments.

References

Cheng, Y. M., & Yip, C. J. (2007). Three-Dimensional Asymmetrical Slope Stability Analysis Extension of Bishop’s, Janbu’s, and Morgenstern–Price’s Techniques. Journal of Geotechnical and Geoenvironmental Engineering, 133(12), 1544–1555. https://doi.org/10.1061/(asce)1090-0241(2007)133:12(1544)

Xia, M., Ren, G. M., Zhu, S. S., & Ma, X. L. (2015). Relationship between landslide stability and reservoir water level variation. Bulletin of Engineering Geology and the Environment, 74(3), 909–917. https://doi.org/10.1007/s10064-014-0654-0