• Geomechanics and Engineering
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• v.30 no.4
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• pp.325-336
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• 2022

This paper analyzes the ground surface settlements induced by side-by-side twin shield tunnels bored in sedimentary soils, which primarily consist of sand with clay strata above the tunnel crown. The measurements were obtained during the construction of twin tunnels underneath the Incheon International Airport (IIA) located in Korea. The measured surface settlement troughs are approximated with Gaussian functions. The trough width parameters i and K of the settlement troughs produced by the first and second tunnel passings are determined, along with those for the total settlement trough. The surface settlement troughs produced by the first shield passing are reasonably represented by a symmetric Gaussian curve. The surface settlement troughs induced by the second shield tunnel display marginal asymmetric shapes at selected sections. The total settlement troughs are fitted both with a shifted symmetric Gaussian function and the superposition method utilizing an asymmetric function for the incremental trough produced by the second tunnel. It is revealed that the superposition method does not always produce better fits with the total settlement. Instead, the shifted symmetric Gaussian function is overall demonstrated to provide more favorable agreements with the recordings. Therefore, the shifted symmetric Gaussian function is recommended to be used in the design for the prediction of the settlement in clays caused by twin tunneling considering the simplicity of the procedure compared with the superposition method. The amount of increase in the width parameter K for the twin tunnel relative to that for the single tunnel is quantified, which can be used for a preliminary estimate of the surface settlement in clay induced by twin shield tunnels.

• Tunnel and Underground Space
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• v.23 no.5
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• pp.337-346
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• 2013

The characteristics of subsidence above a shallow tunnel excavated in weathered rock mass is analyzed. The tunnel is excavated minimum about 11m beneath some buildings and the width of the tunnel is 11m, too. Subsidence pins are installed at 23 locations on surface along the tunnel, 180m long, adjacent to the buildings. Subsidences are measured for about 2 years and they are optimized to analyze three dimensional deformed ground surface, trough width parameter K and sectional volume loss of unit tunnel length Vs of the surface deformation profile.