| At present,Chinese economy is in a continuous high-speed development period,and the urban subway construction is also developing rapidly.Many projects use shield machine to construct.Shield method works under the ground,not only hardly affects the ground transportation,but also adapts to various complex geological construction.So many advantages make shield method widely used in subway constructions.Although the construction technology and technology level of shield method are making progress, shield method still inevitably produces disturbance on the surrounding soil,causes different ground displacement and deformation.Based on the background of Lanzhou metro line 1,this paper selects the section from century avenue to Yingmen beach,study the influence of shield tunneling construction on surface deformation,contrastively analyze the influence of different quantified layers thickness and tunnel face thrusts on surface settlements,mainly obtains the following conclusions:(1) In the process of shield excavation,the surface in a certain distance at the front of the excavation face heaves,and the surface at the behind of the excavation face subsides.The surface heaves in about 12 m at the front of the excavation face.With the shield tunnel excavation,the soil behind the excavation face will appear further subsidence.Then the ground surface settlement of the starting excavation face remains at about 19 mm,with a steady state.(2) The stratum settlement above the excavation face increases gradually from the surface to the tunnel vault.The stratum settlement and uplift reach the maximum in the tunnel vault and the tunnel invert,respectively.(3) The maximum lateral settlement caused by shield excavation is located at the tunnel axis,and the surface settlement of the excavation face accounts for 42% of the final settlement in that place.(4) Using the peck formula to calculate,compared with the ANSYS simulation results by plotting in figures.when the ground loss ratio is 0.35%,the maximum lateral settlement is8.1mm,and the result is closed to the simulation result.By amending the settlement trough width i in peck formula,it can be obtained a theoretical value curve which is closer to the ANSYS simulation results.(5) Different quantified layers thickness will cause different surface settlements.The thicker the quantified layer,the bigger the surface settlement.With the diminish of the quantified layer,the surface settlement will decrease.The change of the quantified layers thickness has large influence on the surface deformation near the tunnel axis.(6) Different tunnel face thrusts will also cause different surface settlements.The bigger the tunnel face thrust,the bigger the surface longitudinal settlement.With the excavation of thetunnel,the difference values of surface settlement caused by different tunnel face thrusts are getting smaller,while the uplift at the front of excavation face have obvious difference.(7) In actual construction,field investigation and geological condition should be done well before excavation;the reasonable soil cabin pressure should be set in the process of excavation, the tunnel direction should be controlled well and adjusted in time as required;the residue soil should be improved and the synchronous grouting and secondary grouting must be completed well;after excavation,comprehensive analysis and judgment of stratum risk must be provided and the corresponding measures must be taken timely and effective.In addition,the establishment of contingency plan system is also essential. |
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