| As the first super large diameter river crossing tunnel in Anhui Province,the construction of Wuhu Chengnan River Crossing tunnel will face the problems of high construction difficulty,high risk and complex geological conditions,etc.It is of great practical significance to carry out the research on the excavation disturbance effect of the super large diameter shield tunnel.In this paper,the disturbance effect of the excavation process of the oversized diameter tunnel in the initial section and the crossing Yangtze river section is simulated and analyzed by using FLAC3D software and the numerical method of hydraulic-mechanical coupling based on the fluid flow simulator TOUGHREACT for the characteristics of Wuhu Chengnan River Crossing tunnel in complex geological conditions,taking into account the shield tunneling process elaborately,the anisotropic characteristics of rock strength and the hydraulic-mechanical coupling effect.The main research conclusions are as follows:（1）The simulation results of tunneling in the initial reinforced section show that comprehensive reinforcement measures of triaxial mixing pile,high pressure rotary jet grouting pile,plain wall and 3m frozen zone could effectively reduce the deformation and damage of the broken right line tunnel portal.The surface vertical displacement in half of the reinforced section（10m from the wall）is the largest,and the ground surface deformation is obviously affected by the face pressure,elastic modulus of the reinforced soil and the shield shell.The surface settlement decreases with the increase of soil elastic modulus.The maximum simulated value of the ground surface is 12.23mm during the shield is excavated 50m,which is in good agreement with the measured value of 13.00mm.The excavation of the left-line will cause the maximum settlement value of the ground surface to increase further,and the affected area is mainly located between the central axis of the two lines.（2）During the shield crosses the embankment,the natural situation will produce a wide range of shear damage at the bottom of the embankment,and the maximum settlement value of the surface reaches 30.18mm,while only a small plastic zone appears at the top of the tunnel after taking pressure-dense grouting measures,and the maximum simulated settlement value at the top of the embankment is reduced to 20.46mm,with a drop of 32%.Because of considering the reinforcement effect of simultaneous grouting on soil,the simulated value is large compared with the measured value of 16.86mm,indicating that the pressure-dense grouting measures can effectively control the surface settlement.（3）tunnel excavation,the ground settlement under the river is influenced by the change of river water level,hydraulic-mechanical coupling,the distribution of initial microcracks in the rock mass and the water pressure of the support.Without considering the hydraulic-mechanical coupling,the surface settlement at the bottom of the river does not exceed 10.00mm,while the considering hydraulic-mechanical coupling,the surface settlement at the bottom of the river increases significantly with the increase of the river level,reaching 36.00mm at 0m river level and 49.00mm at 12m river level,and it shows that with the increase of the water level,the effect of river seepage on the ground subsidence is more obvious.During the initial microcracks in rock mass are preferentially developed horizontally,the maximum surface settlement value increases to 23.00mm in the area far away from the excavated tunnel.Without considering the hydraulic coupling,the increase of ground settlement caused by the change of support water pressure does not exceed 14.10mm,while the increase of ground settlement reaches 18.50mm during considering the hydraulic coupling effect,which indicates that the support water pressure can effectively control the ground settlement at the bottom of the river,and the most suitable support water pressure is about 0.50MPa during considering the hydraulic coupling effect. |
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