Study On The Ground Surface Settlement Of Large-span Metro Tunnel With Shallow-buried Tunneling Method

Ground surface settlement of large-span metro tunnel by using shallow-buriedtunneling method is one of the worldwide concerned and most difficult controllingkey problems in the design of tunnel constrution in cities, and it is urgent to be solveddue to the need of constructions of large-span metro tunnel. Ground surfacesettlement is usually thought to be caused by volume losses of the stratum. Tunnelexcavation under the ground surface will inevitably disturb the surrounding soil mass,then, the state of equilibrium is broken, and the deformation is caused. When thedeformation is large, the upper buildings and ecological environment will bedestroied, even the lives and properties of human beings will be endangered.However, up to now, the settlement prediction and disposal measures, of largedeformation are still problems. Further study on the characteristics and variations ofground surface settlement of metro tunnel as well as mechanism of deformationshould be carried out, then reasonable settlement pridiction and effectiveprecautionary and disposal measures should be advanced, which are very significantto the design, construction and operation of metro tunnel. In this thesis, theoreticalanalysis and numerical simulation are performed to study the variations and themechanism of settlement at the ground surface with the background of line 2 ofmetros in Guangzhou City.First, reasonable construction sequences and steps are proposed according to theshallow-buried large-span metro tunnel in soft soil in Guangzhou, then they are putinto practice, and the results is acceptable. Moreover, the suggested excavationsequences and steps are a construction guide of similar tunnels.Second, finite element method of plane srtain is used to simulate theconstruction steps and processes of the metro tunnel, and the ultimate settlements atthe ground surface in different construction steps are smaller than those suggested instate codes. Therefore, the proposed excavation sequences and method are effectiveand applicable in the construction of line 2 of metro tunnels in Guangzhou. Finally, comparison of results from numerical simulation and data from fieldmonitoring show that the suggested excavation method is reasonable, and thefeasibility and applicability of the method of numerical simulation advised in thisthesis is also verified. In addition, the ground surface settlement of metro tunnel couldbe reduced by using proper job practice.