Research On The Effects On The Deformation Of Adjacent Existing Tunnel Due To Shield Crossing Construction

With the proposal of the strategy of building Chinese strength in transportation,the pace of developing urban rail transit in China has accelerated.In order to make full use of underground space,there are more and more subway tunnel construction projects in cities.The shield method is commonly used in building subway tunnels due to its advantages of safe excavation,fast tunneling and high automation.However,the surrounding soil will inevitably be disturbed,resulting in the destruction of the balanced stress field and displacement field in the original stratum when the shield machine is advancing.Then it will also have adverse effects on adjacent existing tunnel structures,such as cracks,water leakage,uneven settlement or heave and other phenomena,which will affect the stability and safety of tunnel system.Therefore,it is of great engineering significance to reasonably and quickly predict the impact on adjacent existing tunnels due to new shield constructions.On the basis of previous studies,this paper researches the deformation responses of adjacent existing tunnels under the influence of newly tunneling(including single tunneling below,single tunneling above and twin tunneling below)by theoretical methods.The main research work and corresponding conclusions are drawn as follows:(1)Based on Rayleigh-Ritz method and energy method,a new simplified method is proposed to calculate the longitudinal deformation of existing tunnel caused by tunnel crossing construction by combining Euler-Bernoulli beam and Pasternak foundation model.The results show that this new method has high calculation efficiency and can meet the calculation accuracy requirements without taking multiple numbers.The deformation of existing structures can be quickly evaluated by adopting the proposed method.(2)Based on the Loganathan-Polous’ s solution,a simplified method is proposed to estimate the longitudinal settlement of the existing tunnel caused by single tunneling below.Two practical engineering cases are employed to verify the correctness of the proposed method.After the validation,the parameter analysis is carried out.It is found that increasing the vertical distance between new and old tunnels can reduce the longitudinal settlement of existing structure.And the same effect can be achieved by reducing the ground loss or the excavation radius.(3)Based on Mindlin’s solution,a simplified method is proposed to evaluate the longitudinal heave of the existing tunnel induced by single tunneling above.Two practical engineering cases are used to verify its rationality.After then,parameter analysis is conducted.It can be seen that the behavior of increasing the vertical distance,the crossing angle between new and old tunnels or longitudinal equivalent bending stiffness of the existing tunnel can achieve the same positive effect on longitudinal heave control of existing tunnel.(4)Based on Peck’s,Mair’s theory and Hunt’s twin-tunnels construction theory,the analytical method considering the difference in ground loss caused by the two constructions of twin-tunnels is proposed to assess the longitudinal deformation of existing tunnel.The effectiveness of the method is verified by comparing the calculated results with the measured data from twin-tunnels undercrossing project.On this basis,the parametric study is caried out.It is shown that the difference in ground loss caused by the asynchronous construction of twin tunnels has a significant impact on the settlement of the existing tunnel.The settlement of existing tunnel will be effectively controlled as the center distance between twin-tunnels and clear distance between new and existing tunnels increasing.However,the behavior of increasing the diameter of the new tunnel has the opposite effect.