| Deep excavation engineering is a huge systematic project. It is designed both toensure the safety of retaining structure and to reduce engineering cost. In order toharmonize the relationship between the cost and reliability of engineering, theoptimization design of retaining structure for deep excavation was born. Many problemsexist in the optimization design, for example,1. The optimization design of retainingstructure usually comes down to a great lot kind of design variables and combinationvariables, including continuously variable and discrete variables.2. The relationbetween optimization target and design variables is relatively complex. Since thesensitivity of design variables towards optimization target are abhorrent, it is difficult toestablish the dominant relationships between them. As a result, to search for aoptimization algorithm is key. For the sake of the optimization design of retainingstructure, its contents involve primarily the following aspects:①It is necessary toestablish the optimization design model for retaining structure of deep excavation.②The calculation method of earth pressure for different retaining type are described.③The mechanical model for retaining structure of deep excavation was set up.④A newoptimization method based on genetic algorithm for solving this model is presented.Thus, With the support of the country “11th Five-Year Plan” to support science andtechnology project-Study on the Optimization Design System and EngineeringDemonstration of Retaining Structure for Deep Excavation, the above-mentionedproblems were chosen as research project, which has important academic significanceand application value.①The optimization design of retaining structure was mathematically described.The content was proposed which including selection of design variables, determinationof rectrained conditions and construction of objective functions. According to analysethe relationship among design variables, the range of preliminary values of designvariables are given for constraint conditions. Finally, the optimization model wasestablished.②In order to solve the optimization design model with constraint condition, thecalculation methods of earth pressure and security for different retaining type aredescribed. First, based on the limit equilibrium theory and the hypothesis of planarsliding surface, a formula was proposed to compute the lateral earth pressure of soilnailing wall. Then, the earth pressure principle of row piles and diaphragm wall considering the effect of the soil arching is researched, and the two shapes of minorprincipal stress arch are theoretically analyzed. According to the shapes of minorprincipal stress arch, the coefficients of earth pressure corresponding to different angleof internal friction and that of wall friction are gained. Using the method of horizontaldifferential elemeng the theoretical formula for active earth pressure on retainingstructure, the resultant earth pressure and its acting point are obtained and comparedwith the Coulomb’S formula, the previous methods and some experimental observations.This overcomes the shortcoming involved with existed active earth pressure theory thatconsider soil arching effect but takes no consideration of the influence of the internalfriction angle on the inclination of sliding plane of soils behind retaining structure.③Different calculating methods are put forward based on the stability analysis ofthree different kinds of support structure in deep foundation pit. Firstly, the formula ofminimum safety factor and search model of the most dangerous sliding surface areobtained by means of Simple-Swedish Slices Method for the stability analysis ofsoil-nail support structure in layered uneven soil; then, stiffness of the elastic foundationbeam model in row-pile support structure is figured out by the Mindlin formula used forthe horizontal and rectangular load in the elastic half-space, theoretical formula ofinternal forces and deformation can be obtained. Lastly, forcing cases of undergroundcontinuous wall can also be indicated by the displacement solution of strip load in thematrix displacement method based on the deduced Melan formula used for thehorizontal and linear load in the elastic half-space, meanwhile, taking the excavationand lateral brace into consideration step by step, the loads on the support structure arecorrected by the increment method, which can obtain the more actual displacement anddeformation.④Based on the crossover operator and mutation operator improved by thedynamic adaptive technology, the new optimized algorithm DAGA is put forward,which can improve the convergence rate&calculating accuracy and can overcome suchdefects as complicated ways in determining the value of adaptability during the processof traditional genetic iteration, early convergence to the local optimized solution and theslow convergence rate nearby the optimized value. On the basis of the new optimizedalgorithm DAGA, the optimized system of soil-nail wall, row-pile and undergroundcontinuous wall is established and the software of optimized design in deep foundationpit is also developed. During the developing process of the software, VC is used tocontrol the data and develop the interface, and Matlab is also used to fulfill theimproved genetic algorithm, combined with the method of COM component. Fulfilled process of such software can successfully solve the technical difficulties inencapsulating the structural design and COM component, which leads to the fulfillmentof the entire functions.⑤The optimization design software for deep excavation has been used in theoptimization design of the project,"the retaining structure for deep excavation of theharbor city of Beijing". In the process of the optimization design, keeping the parame ofprestressed anchor unchanged, the design variables of bracing location, pile diameter,pile spacing, embedded depth and concrete strength grade are optimized.It proves thatthe software has good performance in the optimization design. |
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