Study on Weakening Measures to Improve Cutting Efficiency of Temporary Segment in Shield Tunnel Construction

Due to the difficulty of cutting the temporary segment at the mouth of the tunnel in the construction of shield tunneling method, there are some problems in the construction, such as long tunneling period, difficult to control the attitude of shield machine, and high risk of water and sand gushing. However, there is still a lack of research on the solutions to these problems. Therefore, based on the background of the shield tunnel project of a subway in Tianjin, on the basis of ensuring the safety of the structure during construction and use, this paper proposes three weakening methods from the perspective of weakening the temporary segment, which are to reduce the concrete strength grade of the segment to be cut, reduce the amount of glass fiber reinforcement and drilling the segment. The possibility and influence of weakening were studied by finite element numerical simulation. The results show that: (1) Under the three weakening methods, the internal forces of the special lining ring are decreased in the cutting area, the internal forces of the steel tube area are increased, and the internal forces of the ordinary lining ring are slightly increased. (2) After the temporary segment concrete strength is reduced from C40 to C20, the internal force of the lining ring is affected within 15%, and the internal force of the steel pipe area is increased within 5%. (3) the influence of the main reinforcement amount on the internal force of the segment within 2% is less than 70%. (4) Drilling inside the segment reduces the bending moment of the cutting area by about 30%. Under the same variation of the size of the aperture and the hole depth, the influence of the aperture on the internal force is greater than the hole depth. (5) The structural internal forces weakened by different weakening methods are all within the limit bearing range, and all the three weakening methods can be adopted. From the perspective of construction convenience and safety, the concrete strength reduction scheme of temporary segment is the optimal scheme.