Passenger Green Tunnel Shallow Segment Grew Deep Foundation Pit Optimization And Spatial Effects

With the large number of high-level,ultra-high-rise buildings and underground works emerging constantly, the foundation pit engineering increasingly high demands,at the same time,issues have become increasingly more, so it has prompted the engineering technician to look at the old subject-the foundation pit engineering with a new vision. In this thesis,by means of engineering analogy, numerical simulation and theoretical analysis, the support structure and construction methods of long-large-deep foundation pit engineering are optimized and numerical simulated, basing on Guangzhou JinShaZhou tunnel Open-cut works on Wuhan-Guangzhou passenger line, and then, the simplified calculation method about spatial effect of long-large-deep foundation pit is derived theoretically. Finally, the main factors effecting the spatial effect of long-large-deep foundation pit are discussed. The main content are followed:(1)Based on a wide range of documents and similar projects investigation,the characteristics and suitability of calculation methods and analysis theories about long-large-deep foundation pit engineering, which used in current mainly are studied concretely, and the possible domains of support parameters are summarized under similar conditions, then,an initial optimization objective is proposed by engineering analogy.(2) In accordance with the actual background of JinShaZhou tunnel, the original design scheme is analyzed and calculated in detail by the finite-element method of elastic sub-grade beam, the results indicate that the original design is relatively conservative and have greater optimum space.(3)The multi-objective optimum functions of support structure design are established step by step, the optional value of support parameters under the background are ensured initially. Advantage and disadvantage of three feasible construction methods are compared through theoretical analysis,construction organization and the impact against to environment, then, combined with the actual construction situation, an excavation method named "rolling construction method", which full use of spatial effect, and the corresponding support parameters are designed firstly.(4) To ensure the reliability of numerical calculation, based on the measured data of an exist project, a comparative study is processed among four variety procedures, the most matched one is determined. Then, the change laws of physical indicators, including force and deformation of support structure and soil, and its stability in the entire excavation process of pit are studied preliminarily and evaluated.(5)A three-dimensional model is developed further, the stress,strain behavior and its state of space distribution of support structure and soil are ensured. At last, the safety of pit are evaluated further.(6)Based on the associated flow rule and plasticity upper-bound theory, introducing the concept of equal internal friction angle, the simplified calculation method of spatial effect about long-large-deep foundation pit excavation in the clay soil is derived from two failure modes-pure shear and tension-shear type firstly.Also,the relative calculation formulas are put forward and two projects are analyzed as example, the results indicate that the method is reliability for spatial effect calculation and can use as reference to the similar project design. Finally, a sensitivity analysis about main factors, including pit size,stiffness of top beam and circuit purlin and geological conditions, against to the spatial effect of pit is accomplished, and its change laws are obtained, also, the empirical formula, which can calculate physical indicators with three-dimension from the result of two-dimension directly ,is put forward.