Analysis On Construction Process Of Backward Grouting In Super Large Diameter Slurry Shield

In the construction of urban subways,because shield construction has the advantages of short construction period,high safety,high degree of automation,and low impact on the surrounding environment,it has become the first choice for urban subway construction.During the process of shield tunneling,since the diameter of the cutterhead excavated in front of the shield is larger than the outer diameter of the tunnel assembly segment,when the segment assembly is completed and completely removed from the tail of the shield machine,there will be a gap between the segment and the soil layer.The method of grouting behind the wall is usually used to fill the shield tail gap in time,and post-grouting is an important part of the success of the shield construction.At present,there are still many differences in the form of post-grouting pressure distribution on shield tunnel walls.The mechanism of action on slurry and the surrounding formations and segments is still to be improved.Most of the grouting studies are aimed at small and medium sized shields,and the grouting pressure does not take into account the influence of gravity.There is less research on the post-grouting of super-large diameter slurry shields that have emerged in recent years.This article uses the engineering of Wuhan Tunnel No.7 Sanyang Road crossing tunnel.The finite element fluid dynamics simulation analysis is performed on the grouting system of ?15.76 m slurry balance shield machine and focus on the distribution of slurry pressure under gravity.At the same time,the shield tunnelling process is refined and simulated based on the actual project conditions.Using the new slurry simulation method,the slurry calculation results are compared with the fluid calculation results to verify whether the slurry simulation is reasonable.Then the monitoring data of the displacements of the eight measured points on the specific section surface are compared with the numerical simulation results to verify the reasonable feasibility of the numerical simulation.Finally get the following conclusion:1.The slurry pressure increases linearly along the direction of gravity.The slurry stress gradient and grouting severity are basically consistent.The change of inlet flow rate does not affect the slurry pressure distribution,and the surface pressure of the slurry remains basically unchanged.The slurry mainly moves in a circular motion,and the flow rate of the grouting inlet has a certain influence on the movement of the slurry.When the grouting inlet flow rate is 3:4:3,the injected slurry has less influence on the flow stabilized slurry and less disturbance to the surrounding environment.2.The grouting layer is in a ball stress state and the slurry is evenly compressed.With the shield tunneling,the distance between the top and the bottom of the grouting layer is getting closer and closer to the vertical direction of the shield tunneling direction,and it is compressed in the vertical direction.The grouting layer is displaced more and more in the transverse direction and stretched in the transverse direction.The total volume of the grouting layer is unchanged and the shape is changed.The grouting layer in the central region becomes thicker and the top and bottom grouting layers become thinner.3.The settlement will occur on the surface of the tunnel at the top of the shield excavation tunnel,and bulging will occur on the surface 25 m away from the tunnel midline.With the shield excavation,the surface settlement at the top of the tunnel gradually increased,and the maximum settlement was close to 11 mm.The amount of uplift above the 25 m above the tunnel's centerline gradually increases,and the maximum amount of uplift is close to 9mm.For the LK3+930 section,the shield has a great influence on the displacement of the section surface near the section.