Abstract
By selecting the ratio of the cumulative maximum deformation of the retaining structure to the excavation depth as the control parameter of the retaining structure deformation, this paper established a sidewall unloading model which can consider the deformation of the retaining structure and the spatial effect of foundation pit excavation. Meanwhile, the impact region of the sidewall was divided to calculate the distribution of additional stress caused by foundation pit excavation. On this basis, through introducing the collaborative deformation model for rotation and dislocation of a shield tunnel, this paper studied the longitudinal deformation of the adjacent shield tunnel due to foundation pit excavation. Moreover, several engineering cases were given to verify the reliability of the proposed method, and the influencing factors were analyzed. The following conclusions were obtained: the axial horizontal displacement of the shield tunnel by the side of the foundation pit was normally distributed, and the calculated value was in good agreement with the measured value; the longitudinal deformation of the shield tunnel was mainly induced by the unloading effect of the sidewall of the foundation pit, which was parallel and closed to the tunnel; the soil excavation in the vicinity of the buried depth of the tunnel would result in a significant increase in longitudinal deformation; with the increase in the retaining structure deformation of the foundation pit, the longitudinal deformation of the adjacent shield tunnel and its influence scope also increased; the longitudinal deformation of the shield tunnel decreased with the increase of clearances between the foundation pit and tunnel; and finally, the excavation of the foundation pit had a great influence on the shallowly buried shield tunnel nearby, and the effect of foundation pit excavation on the tunnel decreased with the increase of the burial depth of the shield tunnel.
Highlights
With the rapid development of urban mass transit systems and the exploitation of underground space, excavation projects of foundations located at the side of existing shield tunnels are becoming more common
The effect of sidewall unloading will pass through the soil to the adjacent shield tunnel during the construction of the foundation pit, Symmetry 2020, 12, 2103; doi:10.3390/sym12122103
−NDt where Pax (l) is the horizontal additional load caused by foundation pit excavation along the axis of the adjacent shield tunnel, which can be obtained with Equation (11), and N is the number of shield tunnel segment rings within the calculation range
Summary
With the rapid development of urban mass transit systems and the exploitation of underground space, excavation projects of foundations located at the side of existing shield tunnels are becoming more common. This method has been used to perform some analysis on the response of adjacent tunnels due to foundation pit excavation [17,18,19,20] These existing studies pay more attention to the calculation models of a shield tunnel’s longitudinal structure, which is the key problem in the second stage. In terms of the calculation of the additional stress field caused by the excavation of a foundation pit (the key problem in the first stage), the existing theoretical methods have been simplified a lot [24,25], which cannot consider the influence of the deformation for the retaining structure of the foundation pit and the spatial effect of the foundation pit. In this paper, some influencing factors are analyzed, such as the deformation of the foundation pit’s retaining structure, the clearances between the retaining structure and the shield tunnel and the buried depth of the shield tunnel
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