| With the development of large-diameter shield technology in China,more and more cities have adopted shield tunnels to cross the river and realize the construction of cross-water traffic passages.However,when a large-diameter shield is used to pass through high water pressure and strong permeable boulders,it is difficult to establish a dynamic equilibrium state of the excavation surface under high water pressure and is susceptible to disturbance and instability.At the same time,large-diameter boulders are difficult to establish a dynamic equilibrium state of the excavation surface under high water pressure.During the construction period of the shield tunnel with cross-section,the construction load changes greatly,and the stress state of the segment structure is complicated.The study of the stability of the excavation surface and the safety of the segment structure during the construction period of the large diameter shield tunnel with high water pressure and strong permeable pebble The selection of construction parameters for this type of formation and the optimal design of the segment of the full-section strong water-permeable pebble formation are of great significance.In view of this,based on the Changde Yuanjiang Tunnel Project,this paper uses theoretical analysis,numerical simulation,indoor experiment and field test to study the mechanical behavior of large-diameter muddy water shield tunnels in strong permeable pebble formations during the construction period.The main research work and conclusions include:(1)Using the finite difference method,the fluid-solid coupling analysis was carried out for the two typical formations of the large-diameter slurry shield tunneling through Yuanjiang silt fine sand and round gravel,and the stability of the excavation surface of the two formations under different mud pressure differences was obtained.,By analyzing the change law of the seepage field,displacement field and stress field in front of the excavation under different mud pressure support ratios,the suggested thresholds for the pressure of the mud sump in the two formations are obtained.(2)For the first time,an indoor mud film forming experiment was carried out using the original soil of the round gravel stratum.The ground particles discharged by the on-site shield are used as the test ground(hereinafter referred to as the original soil)as the test ground(hereinafter referred to as the original soil);the independently developed indoor large-diameter mud film forming test device is used to effectively reduce the mud seepage process.The sidewall effect;the mud ratio used in actual construction is adopted.Through the film-forming characteristics of the mud with different mud viscosity under different pressures,the correctness of the value of the pressure in the pebble formation calculated by the fluid-solid coupling is verified,and the influence of the shield grout agent on the mud properties is verified.According to the law,the best mud ratio suitable for the pebble stratum of Changde Yuanjiang Tunnel was obtained.(3)Conduct field tests to study the influence of the buried depth of the tunnel on the force of the segment structure when the shield passes through the full-section pebble stratum,and obtain the external water pressure of the segment ring during the construction period,the ring axial force of the segment and the bending Moment,longitudinal axial force of segment and bending moment change law with time.It is found that the water pressure outside the ring is mainly affected by de-ring and synchronous grouting;while the internal force of the segment will be affected by the pushing force,de-ring and synchronous grouting pressure in turn.Among them,synchronous grouting has the most significant influence on the water pressure and internal force of the segment,and the maximum value of both appears during the grouting. |
