Prediction of Control Effect of Anti-floating Anchor on Shield Tunnel under Foundation Pit Excavation

The inhibition effects of anti-floating anchors that are arranged on the shield tunnel on tunnel uplift are studied. A three-dimensional finite element model of foundation pit excavation above an existing shield tunnel with anti-floating anchors was established. With the consideration of the length, diameter, angle, spacing, and the number of each tube of the anti-floating anchor rods, the influence of different anti-floating anchor layout on its inhibition effect of shield tunnel uplift was analyzed. Meanwhile, considering the excavation condition of foundation pit and the relative position relation between foundation pit and shield tunnel, the effect of anti-floating anchor in different conditions was analyzed. The results show that: The anti-floating anchors arranged on the segments of the shield tunnel have a certain inhibitory effect on tunnel uplift. The inhibition effect of the anti-floating anchor will be better with the longer length, larger diameter, smaller spacing, and more number of each tube of the anti-floating anchor rods. It is sensible if the anti-floating anchor arrangement angle is around 30°. The greater the buried depth of the shield tunnel, the better the inhibition effect of the anti-floating anchor. The greater the length or width of the foundation pit excavation and the greater the excavation depth, the more obvious the effect of the anti-floating anchor.