| The foundation pit engineering of our country is near to world level not in theory aspect, but in design and construction informative management aspect, and moves towards the leading level step by step. Construction foundation pit design optimization now is summarized the pattern of 3 levels of optimization: the first is support structure type optimization; the second is design detail optimization; the third is informative construction process management optimization.The major content of this paper are, first, based on grasping the general situation analysis of the foundation pit, carrying out the optimization of foundation pit support structure type, and summarizing its pattern; second, designing and calculating the optimized support type, and optimizing with grading and optimized method of multi factors, getting the final design scheme; third, carrying out structural design for the optimized design scheme; fourth, analyzing and appraising the scheme, reaching conclusion and suggestion finally. The research of the paper has realistic and practical meaning, as well as theoretical meaning.Optimization of foundation pit support schemeOverview of basic situation of foundation pitThe foundation pit locates the intersectant place of Heishui Road and Nanjing Road of Changchun. Its length is about 55 m, width is about 25 m, and excavation depth is 10.5 and 5.5 m respectively. It is adjacent to road in the north and south, to Yuandong wholesale market in the west, and to programming building in the east. The strata are, from top to bottom, 1-3 m thick of miscellaneous fill, 12-17 m thick of silty clay and clay, 1.2-3.2 m thick of gravel and sand, and cretaceous mudstone below them. Groundwater is phreatic water, and the depth of water level is 1.7-2.25 m.Optimization and determination of support typeBased on the above analysis, according to the summarized optimization pattern, namely:designing support scheme as many as possiblecarrying out scheme selectioncomparising and analyzing selected scheme(4) determining scheme according to the principle of value engineering. The support scheme of this project with this pattern is: using single fulcrum stake anchor support in IH segment, cantilever stake support in IJA segment, soil nailing wall support in HGF segment, slope in the upside and soil nailing wall support in the downside in BCD segment, slope excavation in AB and DEF segments.2 Design calculation and optimization of foundation pit support structure 2.1 Design calculation of slope excavationDesign calculating slope excavation of the southern slope with Taylor chart method, its result is that if the grading angle of slope is 60 degree, then it can satisfy the demand. 2.2 Design calculation of cantilever stake2.2-1 Method of cantilever stake design calculationUsing 4 kinds of method such as Blum, trial method, static balance and limiting equilibrium to carry out design calculation.2.2-2 Calculation results of 4 kinds of design calculation methodThe max moment is 360.4 KN·M, the inserting depth is 5.96 m with Blum method, 350.2 KN·M and 8.20 m with trial method, 94.2 KN·M and 2.15 m with limiting equilibrium method, 443.2 KN·M and 6.75 m with static balance method. 2.2-3 Optimizing with grading and optimized method of multi factors1. The principle of grading and optimized method of multi factorsGrading and optimized method of multi factors is the method that sets some evaluating indexes for design scheme needing analysis and evaluation, and assigns weight according to its degree of importance, then gives a mark to each index in terms of evaluation standard, multiplies each mark by weight and summarizes, reaches the total mark of each design scheme, scheme with the highest mark is the optimal scheme,2. Result of optimizationChoosing 5 evaluating indexes such as cost, construction time, max moment, inserting depth, and displacement of stake top, the optimization result is that Blum method is optimal.2.3 Design calculation of single fulcrum stake anchor2.3-1 Method of s... |
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