| The prevention and treatment of water leakage disaster has always been a difficult task during shallow shield tunnel construction.Once the water leakage disaster occurs,it will have a significant impact on the subway structure stress,structural deformation and ground displacement deformation,which seriously threatens the structural stability of metro tunnel and the safety of train operation.Due to different strata and engineering characteristics in different areas,the design and construction experience in other areas cannot be fully used for reference.In view of the problem of leakage water in shallow shield tunnel,based on the tunnel between Fenglehe Road station and Yulan avenue station of Hefei Metro Line 4,this paper analyzes the mechanical effect of shield tunnel under shallow construction conditions and discusses the influence of shield parameters on shield tunnel construction in soft soil layer by means of literature research,numerical simulation and field monitoring In this paper,the influence of local water immersion in different strata on the mechanical and deformation characteristics of shield structure and the deformation characteristics of strata are studied.Finally,the field test and optimization of segment floating,segment staggering and waterproof technical measures in metro shield tunnel are carried out.The main conclusions of this paper are as follows:(1)The initial displacement of the segment on the right line is not affected by the shallow shield on the left line.After excavation,the maximum settlement of the left line segment occurs in the arch,and the final settlement displacement is smaller than the right line.However,the deformation of segment invert is large,and the absolute value is about 1.6 times of the vault settlement.The horizontal displacement of the shield on the left and right lines is similar,and the horizontal convergence near the middle side is large,which is distributed in the right spandrel of the left line and the left spandrel of the right line.The influence radius of shield excavation on the ground settlement of the left line is about 10 m,and the final ground settlement of the right line is slightly larger than that of the left line.(2)The tension on the arch and invert of the left and right line segments is large,and the tension on the arch waist is small.Under the influence of vertical displacement,the tension of the left line arch and the right line invert is the largest.There is little difference in the compression of the double line segment,the maximum compression is located in the two sides of the arch waist,the maximum value is about 1.3mpa,and the stress of other parts is small.The shear force is the largest at segment arch and waist,but smaller at spandrel and sidewall.The shear force at the left arch waist of the left line segment is the largest,about 0.8 MPa.After the shield tunnel is excavated,the arch is affected by the pressure of the overlying soil layer,and the vertical displacement of the arch crown results in a large tensile force on the lower surface of the segment arch.The plastic zone of shield tunnel is mostly concentrated in the arch waist and side wall,most of which are shear damaged,and there is no plastic zone distribution in the arch crown and inverted arch.(3)The maximum ground settlement monitored on the construction site of the first 100 ring road is-8.83 mm,and the cumulative horizontal convergence variation is-1.9 mm;the maximum cumulative settlement of the arch crown is-9.88 mm.The comparison results show that the measured value is slightly larger than the calculated value,in which the displacement of segment is almost the same as the calculated value,and the measured value of surface settlement is about 36% higher than the calculated value.Considering that the measured values are the largest displacement deformation in the measured values,it can be seen that the calculation process and results of the model are reliable.The research results of this paper not only effectively ensure the smooth construction of shield interval,but also accumulate a certain reference for the follow-up construction of metro lines in this city.(4)Based on the numerical calculation model of different immersion conditions,the paper analyzes the shear stress of the tunnel lining structure under tension and compression,the vertical deformation law of segments and the ground settlement.The main adverse effect of stratum arch soaking on lining structure is the increase of segment shear stress,and the main deformation of lining structure is the significant increase of tunnel arch settlement after the arch is covered with surrounding rock soaking.When one side of double line shield is immersed,the surface settlement grooves are all of “V” type distribution,and when the other side is immersed,the surface settlement grooves are all of “W” type distribution.The plastic zone of surrounding rock under different water immersion conditions has a great development,and the plastic zone of surrounding rock prone to shear failure is developed.The displacement of surrounding rock at the bottom of the tunnel is not affected by the water immersion of the arch,which will intensify the movement of the soil mass towards the excavation position of the tunnel,as shown by the deformation of the segment vault and the increase of the ground settlement.(5)Based on the field investigation,this paper analyzes the causes of the construction disasters,such as the leakage of shield segment,shield tail dislocation and segment damage,and puts forward the technical measures of segment floating,segment dislocation and lining waterproof to ensure the safe construction and operation of shield tunnel.Figure [72] table [16] reference [95]... |
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