With the acceleration of urbanization, underground space development has become an important way to relieve the pressure of urban traffic. In composite formation, the construction of a double-line large-diameter mud-water shield tunnel faces complicated geological conditions and construction problems. Based on the measured surface settlement data of a double-line tunnel project in Hangzhou, this study adopts a mathematical method to perform regression analysis and introduces the correction coefficient α of the maximum surface settlement and the correction coefficient β of the width of the settlement trough to correct the double-line Peck formula. Meanwhile, combining the superposition principle, an applicable correction method for the superposed section of the double-line tunnel in composite formation is proposed. In order to accurately predict the ground settlement law of double-line large-diameter mud-water shield tunnel construction in composite formation. The results show that there is a great difference between the measured value and the predicted value of the Peck formula of the double-line large-diameter mud shield before correction. Examples show that the superposition section correction method can effectively improve the fitting degree of the superposition section prediction curve when the center distance L of the two-track tunnel is greater than (i left +i right). By comparing the corrected coefficient range ofthe Peck formula with different diameters, it can be seen that the large-diameter shield is better than the small-diameter shield in vertical settlement control, and the distribution range of the corrected coefficient of sedimentation tank width is larger than that of the small-diameter shield. The research can provide a reference for the design and construction of large-diameter shield tunnels in China.

In order to reasonably predict the surface settlement caused by the construction of large-diameter slurry shield, this paper conducts regression analysis on the actual measured data in the field and studies the adaptability of Peck's formula in the prediction of settlement of large-diameter slurry shield, while introducing the correction factor α for the maximum surface settlement and the correction factor β for the width of the settlement trough to correct Peck's formula. The results show that: There is a significant difference between the measured settlement value of large diameter slurry shield tunneling in upper soft and lower hard composite strata and the predicted settlement value of Peck formula after linear regression. When the value of α is distributed between 0.1 and 0.5 and the value of β is distributed between 0.5 and 1.0, it can better reflect the surface settlement deformation of large diameter slurry shield in the upper soft and lower hard strata. By comparing and analyzing the correction coefficients of settlement trough for small diameter and large diameter shield tunnels, it can be seen that the variation range of the correction coefficient of settlement trough increases with the increase of the excavation cross-sectional area and the difference in soil properties of the excavation surface. The research results can expand the application scope of the Peck formula and provide a reference for the design and construction of large diameter shield tunnels.

In order to reduce the risk of mud cake formation in large-diameter slurry shield tunneling cutterheads in high clay mineral formations, a three-dimensional numerical model of the shield cutterhead and scouring system is established using numerical simulation methods based on actual engineering. The distribution characteristics of the flow field near the cutterhead were studied, and the angle of the central scouring hole was optimized under multiple working conditions. The results show that: The overall mud flow rate in the center area of the static region ② was higher than that in the outer area. However, there is a significant decrease in the mud flow rate in some parts of the central area, and there is still a risk of the debris from the cutting tools gathering again on the back panel of the cutter head, forming large mud cakes that can block the cutter head; When the scouring angles of the central scouring holes ② and ③ are arranged at 45°, the scouring effect on the outer area is more thorough, and when they are arranged at 90°, the scouring effect on the outer area is the worst; According to the streamline performance factors of the four working conditions in the stationary region ②, rotating region, and stationary region ①, the priority order of erosion angle design can be determined as follows: working condition 2>working condition 3>working condition 1>working condition 4, that is, the order of erosion hole brushing angle is 45°>70°>20°>90°, the research results can serve as a theoretical basis for optimizing the design of the cutter head erosion system.