The active landslide located in the Tavan-Hauthao, Sapa district, Laocai province, Vietnam was investigated using geophysical methods (2D Electrical Resistivity and Tomography), geotechnical investigations, and a ground survey to assess the geologic condition of the sliding block and surrounding ground. Landslide displacement was measured using 15 surface monitoring points. Numerical modeling was done to assess the behavior of an active landslide. This multi-disciplinary approach helped in interpreting landslide stratigraphy, geotechnical characteristics of the sliding groundmass, depth, and nature of the sliding plane. The surface area of the slide is approximately 1200 m². Studying this active landslide is important as it affects the road No. 152, which is an important road connecting the Sapa Ancient Rock Field. This study involved surface topographical survey, surface and sub-surface geological, and geotechnical investigations including Standard Penetration Test and Electrical Resistivity Tomography. Geologic and geotechnical data were used to characterize an active landslide block, which is composed of different soil layers underlaid by granitic rock. The surface electrical-resistivity measurements across the Sapa landslide resulted in inverted-resistivity sections with distinct resistivity contrasts that correlated well with the geology and geo-hydrology observed in boreholes.

1. [1] E. A. Castellanos Abella and C. J. Van Westen, “Qualitative landslide susceptibility assessment by multicriteria analysis: A case study from San Antonio del Sur, Guantánamo, Cuba,” Geomorphology, Vol.94, Nos.3-4, pp. 453-466, 2008.
2. [2] D. J. Varnes, “Slope movement types and processes,” R. L. Schuster and R. J. Krizek (Eds.), “Landslides: Analysis and control (Special reports No.176),” pp. 11-33, Transportation Research Board, National Academy of Sciences, 1978.
3. [3] A. Manconi et al., “Brief Communication: Rapid mapping of landslide events: The 3 December 2013 Montescaglioso landslide, Italy,” Natural Hazards and Earth System Sciences, Vol.14, No.7, pp. 1835-1841, 2014.
4. [4] W. C. Haneberg, W. F. Cole, and G. Kasali, “High-resolution lidar-based landslide hazard mapping and modeling, UCSF Parnassus Campus, San Francisco, USA,” Bulletin of Engineering Geology and the Environment, Vol.68, No.2, pp. 263-276, 2009.
5. [5] A. W. Bishop, “The use of the Slip Circle in the Stability Analysis of Slopes,” Géotechnique, Vol.5, No.1, pp. 7-17, 1955.
6. [6] N. R. Morgenstern and V. E. Price, “The analysis of the Stability of General Slip Surfaces,” Géotechnique, Vol.15, No.1, pp. 79-93, 1965.
7. [7] E. Spencer, “A method of analysis of the Stability of Embankments Assuming Parallel Inter-Slice Forces,” Géotechnique, Vol.17, No.1, pp. 11-26, 1967.
8. [8] D. V. Griffiths and P. A. Lane, “Slope stability analysis by finite elements,” Géotechnique, Vol.49, No.3, pp. 387-403, 1999.
9. [9] S. K. Sarma and D. Tan, “Determination of critical slip surface in slope analysis,” Géotechnique, Vol.56, No.8, pp. 539-550, 2006.
10. [10] Z. Fan et al., “Extension of Spencer’s circular model to stability analysis of landslides with multicircular slip surfaces,” Mathematical Problems in Engineering, Vol.2020, Article No.1298912, 2020.
11. [11] H. Zhang et al., “Modified slip surface stress method for potential slip mass stability analysis,” KSCE J. of Civil Engineering, Vol.23, No.1, pp. 83-89, 2019.
12. [12] Y. Hua et al., “Dynamic development of landslide susceptibility based on slope unit and deep neural networks,” Landslides, Vol.18, No.1, pp. 281-302, 2021.
13. [13] C. Jaedicke et al., “Identification of landslide hazard and risk ‘hotspots’ in Europe,” Bulletin of Engineering Geology and the Environment, Vol.73, No.2, pp. 325-339, 2014.
14. [14] M. Sahana et al., “Rainfall induced landslide susceptibility mapping using novel hybrid soft computing methods based on multi-layer perceptron neural network classifier,” Geocarto Int., doi: 10.1080/10106049.2020.1837262, 2020.
15. [15] B. T. Pham et al., “Improving voting feature intervals for spatial prediction of landslides,” Mathematical Problems in Engineering, Vol.2020, Article No.4310791, 2020.
16. [16] T. V. Phong et al., “Landslide susceptibility mapping using Forest by Penalizing Attributes (FPA) algorithm based machine learning approach,” Vietnam J. of Earth Sciences, Vol.42, No.3, pp. 237-246, 2020.
17. [17] B. P. My and N. V. Hoanh (Eds.), “Geological and Mineral Resources Map of Viet Nam on 1:200.000, Kim Binh–Lao Cai zone (F-48-VIII&F-48-XIV),” Department of Geology and Minerals of Vietnam, 2005.
18. [18] Lao Cai Transport Construction Consultancy Joint Stock Company (LECCO), “Report of technical and geography survey results: The work of upgrading provincial road 152, section Sapa town - Ban Den intersection, belongs to 2nd Mekong Subregion Corridor Urban Development Project (GMS) - Sapa Urban Subproject, Lao Cai city,” 2018.
19. [19] J. Travelletti et al., “Hydrological response of weathered clay-shale slopes: Water infiltration monitoring with time-lapse electrical resistivity tomography,” Hydrological Processes, Vol.26, No.14, pp. 2106-2119, 2012.
20. [20] P. H. Giao and B. X. Hanh, “Analysis of post-landslide electric imaging data at a site in Sapa, Vietnam,” Proc. of EAGE-GSM 2nd Asia Pacific Meeting on Near Surface Geoscience and Engineering, pp. 1-5, 2019.
21. [21] C. F. S. Sharpe, “Landslides and related phenomena,” Columbia University Press, 1938.
22. [22] I. Saunders and A. Young, “Rates of surface processes on slopes, slope retreat and denudation,” Earth Surface Processes and Landforms, Vol.8, No.5, pp. 473-501, 1983.