Study On The Influence And Risk Control Values Of Shield Tunnel Crossing The Existing Bridge Pile Structure

Mechanical response and risk control index of adjacent bridge piles influenced by shield tunnel construction have been investigated in this thesis based on a combination of the theoretical analysis, numerical simulation and experimental results. The detailed research content and main achievements are in the following:(1)The radius of impact area and non-impact area of pile can be defined through comparing the additional stress influential area generated by piles and the influence radius put forward by Randolph. Three-dimensional elastic-plastic finite element analysis has been used to get the optimal values for the tunnel face pressure, grouting pressure in the non-impact area of piles and to correct the calculation expression of the total gap parameter. Combining the optimal value of the shield construction parameters in the non-impact area of piles and the additional stress generated by piles on the ground, the mathematical expressions of shield construction parameter for the impact region of the piles can be achieved. The results indicate that:when selecting the resultant of the static soil pressure as the resultant of the tunnel face soil pressure, and the grouting pressure 1.1 timing the soil and water pressure in deep buried tunnel, the disturbance on the stratum is relatively slight. Additionally, based on the condition of the amount of soil loss in per unit length equaling to the area of the settlement, the expression of the soil loss can be amended.(2)Based on mindlin results, when the three-dimensional soil displacement of excavation surface which caused by the tunnel face pressure converted into the radial displacement, the calculative expressions of the total gap parameters can be achieved to analyze: ①the rate of the soil loss;②the impact of the tunnel radius under soil loss by soil loss rates;③the grouting pressure instead of the uniform confining pressure of cylinder. Assuming the shield tunnel as the cylinder cavity, the cylinder cavity expansion theory has been proposed. The optimal values of shield construction parameters in the influential radius of the pile foundation, the theory of cylinder cavity expansion, the load transfer function with different forms, load transfer constitutive law and coordination of deformation have been used to analyze the mechanical response characteristic of the pile. Simultaneously, the calculative results of the finite element and experimental data are used to verify the tunnel cylinder cavity expansion theory and the rationality, feasibility and applicability of the optimal value of the construction parameters. The results show that:Under the same condition and the load transfer function with different λ=2、4、6, the calculation results of the vertical displacement of the pile foundation are same and the calculation results of the additional axial force and the additional friction of the pile foundation decrease with the increase of A; In different working conditions and with the same load transfer function, when the horizontal distance between the pile foundation and the tunnel increased by 3 m, the pile vertical displacement will decrease about 1.5 mm and the values of the axial force and friction of pile will decline about 0.16×2n-1 In the form of load transfer function, when λ=2, the values of the vertical displacement of the side of pile soil, the vertical displacement of pile foundation, the additional axial force and the friction of the pile foundation value are similar to the finite element calculation results; the analytic calculated reduction factor of pile tip stratum is larger than that of the experimental obtained. With the increase of the horizontal distance of tunnel and pile foundation, the reduction factor of pile tip stratum stress increases while that of the vertical bearing capacity of the pile foundation decrease.(3)The calculation parameters of bridge bearing capacity can be obtained according to the "highway bridge bearing capacity checking evaluation regulation; Finite element method is used to calculate the residual bearing capacity of the bridge structure and structural internal force; when the internal force of bridge structure less than the remaining bearing capacity of the bridge structure, the difference value of the bridge will be selected as the indicators for the final risk control of a project; according to the deformation response of each stage of the control step of shield tunnel under construction, risk control indicators will eventually be assigned to each control step and the risk control of each stage of the project will be obtained. The two-hole shield tunnel from the subway station Gongzhufen to Xidiaoyutai station crossing the Pratt & Whitney bridge project is chosen for the simulation analysis. The results show that the ultimate risk control indicators of the project is that the abutment vertical amplitude differential settlement is no more than 10.0mm; margins abutment vertical differential settlement is less than 5.0mmm; abutment horizontal displacement is also less than 5.1mm; the vertical risk control indicators of abutment stage is significantly higher than that of the vertical margins abutments, but the horizontal risk control indicators of them are closer.