Abstract
Abstract. In recent years, leakages in aged pipelines for water and sewage in urban areas have frequently induced ground loss, resulting in cavities and ground subsidence, causing roadbed settlement greater than the allowable value. In this study, FLAC3D, which is a three-dimensional finite-difference numerical modeling software, is used to perform stability and risk level assessment for the roadbed adjacent to urban railways with respect to various groundwater levels and the geometric characteristics of cavities. Numerical results show that roadbed settlement increases as the diameter (D) of the cavity increases and the distance (d) between the roadbed and the cavity decreases. The regression analyses results show that, as D∕d is greater than 0.2 and less than 0.3, the roadbed is in the status of caution or warning. It requires a database of measurement sensors for real-time monitoring of the roadbed, structures and groundwater to prevent disasters in advance. As D∕d exceeds 0.35, the roadbed settlement substantially increases and the roadbed is in danger. Since this may result in highly probable traffic accidents, train operation should be stopped and the roadbed should be reinforced or repaired. The effects of groundwater level on roadbed settlement are examined and the analysis results indicate that roadbed settlement is highly influenced by groundwater levels to an extent greater than even the influence of the size of the cavity.
Highlights
Urban railways in South Korea have been initiated from the first Seoul subway line in 1974 and have been operating in Seoul and several metropolitan cities
Ground settlement for 4 and 6 m diameter cavities located at a distance of 20 m from the roadbed (Fig. 9a and b) satisfies the allowable value for groundwater levels (GWLs) = −4 and −12 m, respectively
The ground settlement for 8 and 10 m diameter cavities located at a distance of 25 m from the center of the roadbed (Fig. 9c and d) has substantially decreased as the GWL is 8 and 15 m below the ground surface, respectively, and satisfies the allowable value as its level is 18 and 22 m below the ground surface, respectively
Summary
Urban railways in South Korea have been initiated from the first Seoul subway line in 1974 and have been operating in Seoul and several metropolitan cities. The ground subsidence (Fig. 1a) occurred with a cavity with a depth of 5 m, width of 8 m, and length of 80 m near the Seokchon subway station in Seoul. The ground subsidence (Fig. 1b) was caused by the leakage of a water pipeline with a large-scale cavity with a depth of 21 m, width of m, and length of m near Bakchon subway station in Incheon (Newshankuk, 2016). As a cavity exists adjacent to the roadbed, in this study, a three-dimensional numerical analysis using FLAC3D is carried out to assess both roadbed stability and risk level with respect to the distance between the center of the roadbed and the center of the cavity, diameter of the cavity, and GWLs
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