Undrained stability of dual tunnels in layered soils with different strength

The stability of dual circle tunnels buried in layered soils with different shear strengths was investigated by using finite element limit analysis (FELA). The emphasis of this study is in quantitating that the existing tunnels affects the newly-built one, and design suggestions have been provided especially in the optimum location of construction. By imposing a FELA modelling, the variation trends of undrained bearing capacity with different influential factors, including the horizontal distance, vertical distance, the thickness of the top layer, the shear strength ratio of the layered soil, were further investigated. It is concluded that there exists an inclination-fixed worst-band, in which there would be a worst undrained stability once the bottom tunnel was constructed in the band. It is interested that the inclination seems constant by varying several factors but the horizontal distance would be changed with the soil properties. In addition, three patterns of collapse were summarized.

Automated summary

The stability of dual circle tunnels buried in layered soils with different shear strengths was investigated using finite element limit analysis (FELA). The study quantifies the influence of existing tunnels on newly-built ones and provides design suggestions, especially in terms of the optimum construction location. By using FELA modelling, the variation trends of undrained bearing capacity under different influential factors were further investigated. It was concluded that there is a specific inclination-fixed worst-band, where the worst undrained stability occurs once a bottom tunnel is constructed. Interestingly, the inclination remains constant while the horizontal distance changes with the soil properties. Additionally, three collapse patterns were summarized.