[H-DS05] Landslides and related phenomena

[HDS05-P16] The rainfall-induced instability of landslide deposit in Jiuzhaigou cultural heritage site after the 2017 Ms 7.0 earthquake Base on site scour test

*Shenghua Cui¹, Tao Jiang¹, Xiangjun Pei¹, Jing Liang^1,2 (1.State Key Laboratory of Geohazard Prevention and Geoenvironment Protection,Chengdu University of Technology, 2. China Railway Eryuan Engineering Group Co., Ltd.)

Keywords:Jiuzhaigou cultural heritage site, landslide, rainfall, erosion,, ecological geological environment

The Jiuzhaigou cultural heritage site in China is famous for its stunning calcium lakes, waterfalls, and a large-scale karst water system, considered the "king of water scenery". In 2017, a Ms7.0 earthquake caused 89 geological hazards, destroyed vegetation over 132 km², and led to 55 km² of soil erosion. The earthquake also damaged 27 heritage sites and caused 45 Í 10⁴ m³ of water landscape to disappear. This was the first time a strong earthquake occurred at the heritage site in China, making it an important area for ecological geological environment protection and restoration research. Post-earthquake rainfall triggered instabilities in landslide deposits, which led to frequent debris flows entering lakes and lowering the hydrological landscape's quality. This study uses remote sensing images from 2017 to 2020 to investigate earthquake-induced landslides and post-earthquake debris flows, studying infiltration characteristics, erosion, and migration through on-site scouring experiments. The cultural heritage area's steep slope landslide deposits are composed of high fine-grained content and good permeability. The study revealed that the erosion of the sedimentary slope includes surface erosion, undercut erosion, source erosion, and lateral erosion. The wetting front's downward extension increases the slope volume's water content and pore water pressure, while the matric suction continuously decreases after fluctuating in a narrow range. After the water pressure peaks, the sediment reaches a dynamically stable state. The study suggests that the rapid formation of landslide deposits is due to an increase in water content, a sharp increase in pore water pressure, rapid decrease in matric suction, and intense runoff erosion. The study also highlights the importance of rainfall monitoring for landslide deposits due to the high rainfall concentrated in a short time being a significant cause of instability.