Deformation Analysis And Control Of Existing Shield Tunnel Caused By An Adjacent Tunneling On Top

With the rapid expansion of urban population and the intensive use of underground space, the interplay problems between underground structure become increasingly prominent. Based on the engineering experience and research results of existing urban rail transit construction projects, combined closely with the Beijing CBD area yintai to hang hua underground pedestrian through the the subway line10on the top, through theoretical analysis, numerical simulation, model test, field test, deformation analysis and control of existing shield tunnel caused by an adjacent tunneling on top were mainly discussed. The main work and the results were as follows:(1) Using numerical simulations and model test to predict deformation rules of the existing shield tunnel caused by an adjacent tunneling on top. Numerical results showed that:as the upper tunnel excavated, the deformation of the existing structure will experience quickly, slowly fall as follow, and the deformation become stable finally. Model test results showed that earth pressure reducing value of the upper tunnel is bigger, and the earth pressure reducing value of the intersection section is bigger than that of intersection section sides, being consistent with numerical calculation. On the basis of this deformation value the reasonable tunnel excavation scheme and the soil reinforcement scheme were determined.(2) Based on the orthogonal experiment theory, construct the orthogonal experiment. Study showed that span ratio, clip soil thickness has effect on the buoyancy value of tunnel. Combined with practical engineerings, the evaluation indexes such as arch rise value, arch bottom float value, tunnel radial relative displacement, the tunnel vertical relative displacement were proposed. The results of variance analysis and poor analysis also showed that clip soil thickness has significant effect on on the buoyancy value of tunnel, providing the basis for the design of reasonable grouting design.(3) Establish the analytical model which through the existing tunnel on top, and deduce the formula of lateral deformation curvature of the existing shield tunnel with the circumstance of up unload, then analyzed the cross-section safety of the existing tunnel in the practical engineering. Establish the vertical force model of the existing shield tunnel with the circumstance of up unload to deduce the deflection, rotation, bending moments and shear of the existing tunnel caused by up unload with the circumstance of single and double spring model. Then analyze the applicability of the double spring model with actual engineering. This study found that the float value calculated with single spring model is bigger than the value calculated with double spring model.(4) Based on field monitoring, the structural deformations of existing subway tunnels which are up-crossed by tunnel with large cross section mainly conclude floating deformations and minor deformations of structure body. Variation for vertical displacement and level convergence of tunnel structure and vertical displacement of ballast structure keeps the similar rules:fast lifting area, fast dropping area, fluctuation dropping area and post-fluctuation stabilizing area. With the conditions of similar engineering geology and hydrology geology, the span ratio of the western tunnel is0.75comparied with0.95in the eastern tunnel. It is revealed that the vertical displacement of east-line tunnel (2.3mm) is obviously less than the west-line (4.1mm) by field monitoring, thus explaining that span ratio has much more influence on deformations, which are in accordance with the results of orthogonal test.(5) Based on the testing of existing shield tunnel’s condition, the state of the existing tunnel is got. Relying on the prediction of numerical analysis and controlling the construction process of new tunnel with the principle of variable allocation, we control the float value of the existing tunnel successfully. By strengthening grouting and advance support, the rate of deformation of existing tunnel is reduced; the tunnel’s moment is also reduced. The studies showed that the numerical prediction, division displacement control and enhancing the on-site measurements is very necessary and effective in the project of thronging the existing line.