| More and more high rise buildings and large-scale public structures are beingbuilt in recent years. A lot of deep foundation pits are appeared and the size and depthare increasing. The building construction meets problems of restrict control on sitearea and circumstance protection. There are dense buildings, large number of urbanground pipes around most of these pits. In result, Top-Down Construction Method(TDCM) is getting more and more application, as an effective method. However, theTDCM has complex construction organization, and many courses. Whether on theoryor practice, there are quite lot of problems and questions in TDCM need to be solved.There are important theoretical significance and practical value to study on thetechnology and calculation of structure in TDCM, in order to ensure the safety ofengineering and people's lives. This dissertation is carried out research andinvestigation on the base of the largest deep pit engineering of Shanghai—thefoundation pit of Zhongsheng Commercial Center. Some conclusions and resultswhich can be used to guide practice are made.Firstly, some design theories of TDCM are discussed. They are calculation ofpressure of soil and water; the confirmation of level and vertical bearing capacity, theratio between depth and thickness, settlement of diaphragm wall; calculation of loadand bearing capacity of different formal pillars; the design of the sustain beam andsolepiece.Secondly, some key techniques of TDCM are studied in this dissertation. Ondiaphragm walls that are used as a part of main structures, the structure of joints andquality control were extensive analyzed. On pillars, joint structures between pillarfeet and pile cap, the supporting load ways and the uprightness are researched. On theexcavation construction, the dissertation discusses the excavation method and theorganization of construction. On the joint structures between beam and pillars,diaphragm and basement beam or plate, diaphragm and upside wall, pillars andsolepiece are researched.Thirdly, the basin opening excavation method and the temperature crack areresearched by FEM. On the excavation construction, the influence of width ofobligating soil slope shoulder on deformation of diaphragm is extensively researchedand the economical and rational width of soil slope shoulder in soft soil is obtained.In addition, stabilization of obligating soil slope is analyzed by strength reductionfinite element method and the safety factor is calculated. The creating mechanism oftemperature crack in solepiece constructing is researched by multi-physical fieldcoupling FEM and the time of the most difference in temperature between inside and surface in concrete is calculated. Some interrelated control treatment is broughtforward.Fourthly, the computer simulation theory that can simulate TDCM constructionsequences is discussed and successfully applied. It chooses the nonlinear rheologicalconstitutive relation of soft soils, determines corresponding parameters, uses 3-Dplate elements to simulate diaphragm wall, adds contacting elements between soilelements and diaphragm wall elements, adds simulated initial stress in soil, andapplies nonlinear rheological FEM theory to simulate 3-D excavation andsuperstructure construction progress.Fifthly, four processes in information-based construction (monitoring-reverseanalysis-predicting-control) are investigated. The reverse analysis of soil parameterbased on genetic algorithms, forward calculation to predict and pertinence control bypredicted result are discussed.At last, the full course construction of Zhongsheng Commercial Centerfoundation pit that adopt "normal centrally and top-down around" constructionproject is analyzed applying the 3-D nonlinear FEM theory introduced above.Through contrasting between calculated result and actual measured data, someconclusions that can provide theoretic basis are obtained.
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