Abstract
This paper assesses the risk of land subsidence related to the underground Karst caves at the section Km55+660- Km55+690 of North-South Vietnam Expressway by finite element method using PLAXIS 2D V.8.5 software. The research results show that there is a risk of collapsing the ceiling of the underground Karst caves due to the impact of the embankment process and the vehicle load. The research results also show that the vertical displacement is larger than the allowable residual settlement according to Vietnamese standard; it is necessary to take the soft soil improvement to achieve the allowable residual settlement. Several construction solutions are proposed to prevent the risk of land subsidence in the research section. In particular, flyover through the section with underground Karst caves is the most suitable solution.
Highlights
The section Km55+660- Km55+690 of North-South Vietnam Expressway is located in Phong Son commune, Phong Dien district, Thua Thien Hue province, Vietnam (Fig.1)
Researches in the world and in Vietnam show that land subsidence caused by material from covered soil layers being swept into the underground Karst space is very common, occurs suddenly, and is the most dangerous form of the risk, while the ceiling collapsing of the underground Karst space is very rare and occurs for a very long time
The influence of embankment and vehicle loads on the risk of land subsidence is considered at 02 geotechnical sections meeting underground Karst caves, the sections No I-I and II-II (Fig. 4), considering the most unfavorable case when the caves are interconnected by finite element method using PLAXIS 2D V.8.5 software
Summary
The section Km55+660- Km55+690 of North-South Vietnam Expressway is located in Phong Son commune, Phong Dien district, Thua Thien Hue province, Vietnam (Fig.). During the geotechnical investigation for technical design and construction of the Expressway carried out in 2020 and 2021 at the section, underground karst caves were met at the location of boreholes BH01, BH02 and BH03 Some researches by Milanovic (2000), Waltham and Lu (2007), Waltham (2008), (Awadh et al, 2013), and Abdula (2021). These researches have introduced the concept, definition, and classification of the land subsidence in the Karst regions and Karst morphologies.
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