The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation a...The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation at these joints.Existing modeling methods typically rely on the Euler-Bernoulli beam theory,only considering the bending effect while disregarding shear deformation.Furthermore,the constraints on the shield tail are often neglected in existing models.In this study,an improved theoretical model of tunnel floating is proposed.The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam.Furthermore,the Timoshenko beam theory is adopted,providing a more accurate description of tunnel deformation,including both the bending effect and shear deformation,than existing models.Meanwhile,the buoyancy force and stratum resistance are calculated in a nonlinear manner.A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters.The proposed theoretical model is validated through five cases using sitemonitored data.Its applicability and effectiveness are demonstrated.Furthermore,the influences of soil type,buried depth,and buoyancy force on the three key indicators of tunnel floating(i.e.the maximum uplift magnitude,the ring position with the fastest uplift race,and the ring position with the maximum uplift magnitude)are analyzed.The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.展开更多
Due to the network planning of subways and their surrounding structures,increasingly more overlapping shields with a small curve radius have been constructed.A newly constructed upper tunnel partly overlaps a lower on...Due to the network planning of subways and their surrounding structures,increasingly more overlapping shields with a small curve radius have been constructed.A newly constructed upper tunnel partly overlaps a lower one,leading to the extremely complex uplift of the lower tunnel caused by the construction of a new tunnel.Based on the shield-driven project that runs from the Qinghe Xiaoyingqiao Station to the Qinghe Station in Beijing,which adopts the reinforcement measures of interlayer soil grouting and steel supports on site,in this study,the uplift pattern of the lower tunnel and the stress characteristics of steel supports were investigated through numerical simulations and on-site monitoring.The study results show that among all tunnel segments,thefirst segment of the shield witnesses a maximum uplift displacement that increases with the horizontal space between tunnels.On using either interlayer soil grouting or steel-ring bracing reinforcement,the uplift of the tunnel lining exceeds the control value;by contrast,when these two measures are jointly applied,the uplift of the tunnel lining does not exceed a maximum value of 4.87 mm,which can satisfy the requirements of deformation control.Under these two joint measures,the soil strength between two stacked shield tunnels can be enhanced and the uplift deformation can be restricted with the interlayer soil grouting.Also,the segmental deformation and overall stability of the existing tunnel can be controlled with the temporary steel supports.The deformation of circumferential supports and segments is closely related to each other,and the segmental uplift is controlled by H-shaped steel supports.With the increase in the horizontal space between twin shields,the effect of the construction would gradually weaken,accompanied by a gradual reduction of the stresses of steel supports.Thesefindings provide a valuable reference for the engineering design and safe construction of overlapping shield tunnels with a small curve radius.K E Y W O R D Sfield monitoring,numerical simulation,overlapping shields,small curve radius,steel support stress,uplift of tunnel lining Highlights•A project of twin overlapping shield tunnels with a small curve radius is introduced.•Protective measures of soil grouting and H-shaped steel supports are proposed.•A 3D model in view of overcutting soils,grouting,and steel supports is established.•The performance of the overlapping shield tunnel with a small curve radius is evaluated.展开更多
基金the National Natural Science Foundation of China (Grant Nos.52379111,51979270 and 52208380).
文摘The problem of shield tunnel uplift is a common issue in tunnel construction.Due to the decrease in shear stiffness at the joints between the rings,uplift is typically observed as bending and dislocation deformation at these joints.Existing modeling methods typically rely on the Euler-Bernoulli beam theory,only considering the bending effect while disregarding shear deformation.Furthermore,the constraints on the shield tail are often neglected in existing models.In this study,an improved theoretical model of tunnel floating is proposed.The constraint effect of the shield machine shell on the tunnel structure is considered using the structural forms of two finite long beams and one semi-infinite long beam.Furthermore,the Timoshenko beam theory is adopted,providing a more accurate description of tunnel deformation,including both the bending effect and shear deformation,than existing models.Meanwhile,the buoyancy force and stratum resistance are calculated in a nonlinear manner.A reliable method for calculating the shear stiffness correction factor is proposed to better determination of the calculation parameters.The proposed theoretical model is validated through five cases using sitemonitored data.Its applicability and effectiveness are demonstrated.Furthermore,the influences of soil type,buried depth,and buoyancy force on the three key indicators of tunnel floating(i.e.the maximum uplift magnitude,the ring position with the fastest uplift race,and the ring position with the maximum uplift magnitude)are analyzed.The results indicate that the proposed model can provide a better understanding of the floating characteristics of the tunnel structure during construction.
基金National Natural Science Foundation of China,Grant/Award Number:52168059Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region,Grant/Award Number:NJYT23103Fundamental Research Funds in Universities of Inner Mongolia Autonomous Region,Grant/Award Number:2023QNJS159。
文摘Due to the network planning of subways and their surrounding structures,increasingly more overlapping shields with a small curve radius have been constructed.A newly constructed upper tunnel partly overlaps a lower one,leading to the extremely complex uplift of the lower tunnel caused by the construction of a new tunnel.Based on the shield-driven project that runs from the Qinghe Xiaoyingqiao Station to the Qinghe Station in Beijing,which adopts the reinforcement measures of interlayer soil grouting and steel supports on site,in this study,the uplift pattern of the lower tunnel and the stress characteristics of steel supports were investigated through numerical simulations and on-site monitoring.The study results show that among all tunnel segments,thefirst segment of the shield witnesses a maximum uplift displacement that increases with the horizontal space between tunnels.On using either interlayer soil grouting or steel-ring bracing reinforcement,the uplift of the tunnel lining exceeds the control value;by contrast,when these two measures are jointly applied,the uplift of the tunnel lining does not exceed a maximum value of 4.87 mm,which can satisfy the requirements of deformation control.Under these two joint measures,the soil strength between two stacked shield tunnels can be enhanced and the uplift deformation can be restricted with the interlayer soil grouting.Also,the segmental deformation and overall stability of the existing tunnel can be controlled with the temporary steel supports.The deformation of circumferential supports and segments is closely related to each other,and the segmental uplift is controlled by H-shaped steel supports.With the increase in the horizontal space between twin shields,the effect of the construction would gradually weaken,accompanied by a gradual reduction of the stresses of steel supports.Thesefindings provide a valuable reference for the engineering design and safe construction of overlapping shield tunnels with a small curve radius.K E Y W O R D Sfield monitoring,numerical simulation,overlapping shields,small curve radius,steel support stress,uplift of tunnel lining Highlights•A project of twin overlapping shield tunnels with a small curve radius is introduced.•Protective measures of soil grouting and H-shaped steel supports are proposed.•A 3D model in view of overcutting soils,grouting,and steel supports is established.•The performance of the overlapping shield tunnel with a small curve radius is evaluated.
