Deep-seated rainfall-induced landslides on a new expressway: a case study in Vietnam

• Published in: Landslides Vol. 17; no. 2; pp. 395 - 407
• Main Authors: Nguyen, Lan Chau, Tien, Pham Van, Do, Tuan-Nghia
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-02-2020; Springer Nature B.V
• Subjects: Aerial surveys; Agriculture; Anthropogenic factors; Caves; Civil Engineering; Computer simulation; Deep layer; Earth and Environmental Science; Earth Sciences; Failure mechanisms; Geography; Geological surveys; Geology; Geomorphology; Groundwater; Groundwater levels; Heavy rainfall; Highways; Human influences; Karst; Karst caves; Landslides; Landslides & mudslides; Limestone; Man-induced effects; Natural Hazards; Numerical analysis; Quarrying; Rain; Rainfall; Rainy season; Recent Landslides; Road construction; Safety factors; Sandstone; Sedimentary rocks; Siltstone; Sliding; Slope; Slope stability; Slope stabilization; Slopes; Slumping; Surveys; Two dimensional analysis; Two dimensional models; Unmanned aerial vehicles; Wet season; Vietnam; Landslides; Causative factors; Cut slopes; Limestone; Plaxis model; Rainfall; Mechanism
• ISSN: 1612-510X; 1612-5118
• DOI: 10.1007/s10346-019-01293-6

In Vietnam, landslides frequently occur on cut slopes along the road system during the rainy season. An understanding of the contributing factors and triggering mechanisms is essential so that effective measures can be taken to stabilize cut slopes and mitigate impacts caused by landslides. This study uses as a research subject the largest deep-seated landslide triggered by heavy rainfall on July 21, 2018, and the subsequent sliding induced by 5-day continuous rainfall events on the Halong–Vandon expressway. We examined the causative factors, failure mechanisms, and characteristics of the landslides through detailed geological investigation, unmanned aerial vehicle (UAV) surveys, and analysis of data from geology, geomorphology, well-prepared documents of rainfall events, and the expressway project. Results show that the heavy rainfall was the triggering factor for both events while slope cutting was the main landslide causative factor. The slump-type landslides occurred on weathered limestone layers that were parallel to the dip-slope direction of the strata. Geological settings of highly fractured and weathered sandstone, siltstone, and limestone combined with the development of karst caves favored the buildup of groundwater levels in deep layers, thereby causing deep-seated landslides. The analysis shows that in addition to geological factors, the landslide occurrences resulted from anthropogenic effects including the improper design of the calculation method for safety factors in road construction and quarrying activities. Site evidence and UAV photos also reveal that the July 21 landslide body on the lower slope was reactivated to travel downward due to the dynamic effect of the subsequent sliding on July 31. Based on numerical analysis using the Plaxis 2D model, an estimated sliding surface similar to the actual plane was simulated for the entire slope. Furthermore, the study presents an appropriate solution that has been applied to slope stabilization.