The Safety Characteristic Analysis Of Supporting System In Deep Excavation In Soft Clay Area

With the development of urban rail transit network in Shanghai, the deepexcavation of metro station is becoming more and more deep, larger, adjacent anddifficult. In order to positively understand the stress law and the safety character ofsupporting system in deep excavation under construction. In this dissertation, throughgathering and analyzing a great lot of field data and making use of forward and backanalysis methods, water and soil pressure of supporting structure, internal forcechangement of braced structure result from the vertical displacement of uprightcolumn and internal force changement of the diaphragm wall in deep excavation insoft clay area are researched and discussed on the basis of the theory of space-timeeffect and the construction of the station in Shanghai Metro Line. Primary contentincludes several parts as follows.1. The failure mode, the failure cause and the disposal measurements ofsupporting system of deep excavation is analyzed comprehensively, and the safetycontrol index of deformation and internal force is compared, analyzed, unified anddefined roundly on the basis of the statistical analysis of the failure cause of abundantengineering accident.2. Based on the existing theory frame and construction operating condition andfield measured data, water and soil pressure of supporting structure is analyzedsystematically, and the computing method of active earth pressure is discussed.3. On the basis of the analysis of the failure mechanism of braced structure, thechangement law of strut force and the maximal strut force of several metro stations isanalyzed. The computing formula of the internal force of the braced structure underthe vertical displacement of upright column is established, the control index of thevertical displacement of upright column is revised and defined by making use of theprinciple of structural mechanics and the ultimate bending moment theory, and thecontrol index of the internal force is accounted under the allowable deformation ofbraced structure. 4. According to the bending rigidity is difficult to be confirmed reasonably incurve fitting method, the computing methods of the bending rigidity mentioned incriterion at home and abroad are gathered and analyzed. On the basis of our countrycriterion short-term rigidity, the reduction formula is brought forward, then thecurvature is gained by fairing spline fit of deviational survey curve of the diaphragmwall, the result of back analysis is contrast analysis with that of field measurement.5. The finite element model is established by using the substructure finite elementmethod considering the time-space effect, and the susceptivity analysis of affectingfactor of the internal force and deformation of supporting structure is carried through,including the bending moment and deformation of the diaphragm wall under theinfluence of the different preloading, thickness, depth, excavation width and the burieddepth of upright column.6. According to the physical circumstance of metro station, the safety evaluationindex of the supporting system is established, and the safety evaluation model isestablished by using the fuzzy synthetic evaluation method. The proposed model isthen applied to a practical project and the safety level is distinguished and the safetycondition is evaluated.