Research On The Stability Of Tunnel Crossing Beneath The Existing Structures

In recent years, with the increasing of urbanization, highway tunnel beneath the city project has achieved the vigorous development. Meanwhile a lot of geotechnical engineering problems would be sprang up. The highway tunnel constructed beneath the existing structures are often happened in the urban area. In order to assure the safety of tunnel and existing structures, it is vital to understand the mechanical effect in tunnel during excavation and the impact on existing structures.The paper mainly relies on highway tunnel beneath the existing ground floor Mall engineering on laodong Street to shengli Street segment in Xinxiang city,Henan province as background. The finite element analysis software ANSYS and FLAC3 D are used to study comparatively on the separate tunnel, double-linked-arch tunnel and double span rectangular tunnel cross section tunnel during excavation,which caused by mechanical effects, including the deformation and internal force of the business street and the early tunnel support structure and so on. Finally, based on the two-span rectangular tunnel section form, the thesis puts forward the construction optimization scheme. Main contents and the results are as follows:(1)According to real situation of the project, he separate tunnel,double-linked-arch tunnel and double span rectangular tunnel construction projects are compared. Surface settlement and business street are determined as main reference volume. Meanwhile the paper considers vault settlement due to excavation during construction the horizontal convergence, inverted arch uplift, the mall structural stress, tunnel primary support stress as the selection criteria for the reasonable construction programme to finalize tunnel. CRD method and advanced reinforcement for rational construction plan in rectangular tunnels are choosed as a reasonable plan in this paper.(2)In accordance with the selected sections, tunnel construction is completed.The result shows that the maximum ground surface settlement point appears on the right of the model and the influence on surface of sphere is within the margin aroundthe each hole axis 20 m.(3)Aiming at the larger surface subsidence and low structure safety coefficient,comparing to the different parameters of ground consolidation,this paper presents a optimization project which glue double span rectangular tunnel is on the base plate of the underground business street. Data shows that the optimization program is effective in reducing the amount of deflection and ground surface settlement. This can provide experiences for similar works;(4)Parameters selected should be paid more attention to in the construction.Within the framework of the corresponding soil should be reinforced. When constructs the double span rectangular tunnel section, the reinforced soil strength should achieve 3-4 times of the original soil. It is not only difficult to achieve in the construction but also need higher engineering cost, and the control effect of deformation is not ideal.