Abstract: In order to study the influence of excavation near shield tunnels on the force of tunnel segments, the mechanism of surrounding pressure change on tunnels caused by nearby excavation is studied. A model of additional confining pressure redistribution is proposed which can describe the process of force-displacement-rebalancing of tunnels, and the calculation formula of additional confining pressure is deduced. The internal force of lining under the corresponding confining pressure is calculated by using the modified routine method. The influence of foundation pit excavation on the confining pressure and internal force of shield tunnels is studied based on the analysis of a practical engineering example, and the influencing factors are analyzed. The analysis results show that confining pressure of the tunnel before excavation presents a "bell shape" distribution. After excavation, the confining pressure on both sides of the tunnel decreases, and the confining pressure on the excavation side decreases more. The excavation of the foundation pit increases the positive and negative bending moments and the positive and negative shear forces of the nearby tunnel, and decreases the axial forces of the arch top and the arch bottom. With the increase of the stress release coefficient of the side wall of the foundation pit, both the absolute values of the additional confining pressure and of the additional bending moment will increase, and the response of bending moment to unloading of foundation pit excavation is more obvious. Shallow shield tunnel is more sensitive to the influence of the excavation of side foundation pit, and the influence of excavation of side foundation pit will decrease obviously when the burial depth of the tunnel is greater than that of the foundation pit excavation. With the increase of the distance between the foundation pit and the nearby tunnel, the influence of the foundation pit excavation on the tunnel will also be reduced.

Key words: foundation pits excavation, nearby shield tunnel, transverse force, redistribution of confining pressure, modified routine method