| Metro shield construction has brought great convenience to urban development, but it also disturbed soil around the tunnel, thereby causing surface deformation. It may endanger the safety of the buildings above the tunnel and even cause serious social impact and economic losses when particularly local surface deformation is large enough. Therefore, it is necessary to study the ground subsidence and deformation resulted from metro shield construction and to deduce a subsidence prediction model in connection with specific engineering geological conditions. This paper combined with the methods of sampling and analysis of surveillance data of land subsidence on the construction site, Peck formula deduction analysis and FLAC 3D numerical analysis. With the purpose of studying the ground subsidence which caused by tunnel shield of Suzhou line 4 Yang Cheng Lake Road to Kim Min Road.The paper also analysis main causes of the subsidence, including summarizing the law according to the subsidence value based on the measured data, working out Peck prediction model of land subsidence which applying to the formation similar to the Suzhou region that resulted from the subway tunnel shield construction. Also carries out the proposed analysis of the subsidence by making use of numerical simulation software. The main contents and results are as follows:(1)The overall situation of the project is introducted firstly, including the basic geology of the study area as well as land subsidence monitoring program and analysis of the measured subsidence. It is found that the lateral distribution of detected surface’s land subsidence, caused by Suzhou metro shield construction, approximately equals to normal distribution. Regression analysis of the measured data is carried out and a good agreement is achieved on the measured surface subsidence and fitted curve, which demonstrates the feasibility of predicting the ground subsidence by the use of Peck formulas.(2)Linear regression analysis is used to fit the measured data curve of lateral land subsidence caused by subway construction under typical geological conditions and the general rules of the lateral surface subsidence is identified. At the same time, the forecast of land subsidence caused by subway construction is made by the use of Peck formulas according to the survey and design data.(3)Through statistical analysis of a large number of measured data, the original formula Peck is modified by the introduction of two correction parameters. The recommended ranges of Peck formula modified parameters are abtained: the maximum land subsidence modified parameter values between 0.3 and 1.3, the modified parameter of settler width coefficient values between 0.7 to 1.4. The modified Peck formula, is verified and can be applied into the subsidence prediction of other section’s construction of Suzhou Metro Line.(4)A finite difference software FLAC 3D is used to set up 3D model. And the calculation and analysis of the land subsidence development due to shield tunnel excavation is carried out. Six sections of the three-dimensional model are selected on the shield forward to 8m, 16 m, 24 m, 32 m, 40 m and 48 m. The effect of stratigraphic disturbance caused by the shield construction process on the ground subsidence is analysed through three aspects of soil longitudinal displacement contours surrounding the shield tunnel, vertical stress distribution contours and plastic zone distribution contours.(5)The corresponding subsidence curves are drawn according to transverse and longitudinal sedimentation of special section monitoring points in the numerical simulation settlement. The results of numerical simulation and actual measurement are substantially coincide, indicating that the use of numerical simulation method can predict the impact of the subsidence, which has reference values to a certain project.(6)On the basis of analysis of land subsidence. The corresponding specific measures under the shield construction case which should be considered when land subsidence happens during the control of tunnel construction has been proposed for the typical geological conditions and construction conditions in Suzhou. |
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