Study Of Optimum-Design Theory And Dynamic Displacement-Controlling Of Deep Excavation

Modern city construction, economy development and technique progress are leading to a higher request for increasing deep foundation excavation 梠ptimum design. So it is necessary to study further basic principle and method of optimum design for deep foundation excavation engineering.1. Based on above aim and the author's several years experience, By applying the optimization theory, the paper proposes the basic principle and approach of optimum design for excavation engineering from the point of view of system engineering, brings forward the four aspects of optimum design in technique, economy, environment and work period and three stages of system optimization, computation optimization and dynamic real-time optimization for optimum design of excavation.2. The concept design is the key phase of the first stage of system optimization. The paper emphatically discusses with emphasis several issues difficulty to answer, such as the determination of the soil parameters, the soil pressure and the safety factor and the reliability of retaining structure, summaries and analyses the main geotechnical problems during the excavation on the four familiar geologic strata of saturation soft soil on the class I terrace of the Yangtze river, aged-clay, expansive soil and loess and investigates carefully the patterns of deformation and destruction of pit slope in the saturation soft soil, puts forward three basic principles of selecting schemes of retaining structure, namely : facing to the problem, facing to the characteristics of excavation and environment.The thesis constructs an index system and hierarchical structure graph of deep foundation excavation through the application of system engineering and establishes multi-objectives blur optimum decision-making model and its application in the actual engineering has been proved to gain superior decision result.3. During the second stage of optimum design, a suitable梒omputation optimization, a suitable calculation method has to be selected at first and detail structures of one support scheme are optimized to formulate the optimum of engineering cost.After discussing several computation methods of three kinds of retaining structures right now in common use, combining the practical example, the thesis establishes optimization model and flow chart of design and computation of excavation by exerting the means of non-linear programming and applies it to one excavation engineering project successfully.4. Based on the construction-process mechanics of excavation engineering, the thesis proposes a principle and method of real-time optimized control for the deep excavation engineering as a dynamic system during its construction stage and studies the basic concept of back-analysis of deep excavation. The paper also establishes theIIIdisplacement back-analysis method and real-time optimum flow chant according lo the theories of flexible foundation beam and mathematics program.Combining with engineering examples, the paper proves that the pit soil's mechanical properties during excavation are changing continuously. So it is just mostly near to the actual only if mechanical parameters of soil are anti-calculated from the latest results of the test and the displacement and internal force of retaining during the next work stage are forecasted using these newly inversion parameters. Then this form the construction-feedback forecast method of measuring continuously, anti-calculating continuously and forecasting continuously which all of these processes are followed in order and advance step by step.5. The paper emphasizes to study the basic principle and intension of displacement controlling design of excavation engineering and point out that the displacement controlling design is demanded urgently with the development of excavation engineering technology, The stage design can optimize the retaining structure further from the point of view of controlling and its core is dynamic design excavation environment the paper discusses and gives some ma...