Stability Analysis Of Deep Excavation Slope Based On Stress～Strain Relation

The stability analysis of tall building deep excavations' slope is always been a very hot and difficult question in Geotechmical Engineering .For all of the deep excavations' slope analysis methods based on limit equilibrium theory can' t reflect the changes of stress and displacement fields, the results can' t reflect the true slope stability of deep excavations . In this thesis the author advised a new method to analysis the slope stability of deep excavations by analyzing the changes of soil stress and displacement during the excavating. This paper works primarily in the following aspects:1.have retraced the theory development of soil slope stability and the study condition about this subject at present .especially some Chinese scholars' works on this subject ;have analyzed the shortcomings of using limit equilibrium method to analyze the stability of deep excavation slope and the strongpoint of analysis by using finite elements method ;have retrospected the history of FEM and some fruits of its usage in the fields of deep excavation . Through the analysis we can conclude that the stability of deep excavation slope can be analyzed by the results of the changes of stress and displacement caused by excavating.2. based on the fruits of others, this paper have explained the theory of progressive failure of soil slope from the angle of strain softening and the cause of this property from the inherent geometrical and physical mechanism ;have built up the calculation model which have considered this property on how to use to the real project ;have settled the stress modification of failure elements during the analysis of the stability of deep excavations by the method of finite elements.3. in this paper , the author have analyzed the changes of stress and displacement fields of soil surrounded the basement caused by excavating through nonlinear elasto~ plastic analysis .In the analyzing , the D-P model of soil based on generalized Misescriterion is used and the gradually excavation have been considered . By the real project analysis , not only the stress of the soil around the deep excavation and the deformation of slope can be obtained , but also the failure area can be located . From the analysis results , some conclusions can be drawn , such as: (l)the largest horizontal displacement on the surface of the deep excavation slop is not on the top of the slope , but on the area where the distance to the corner of the excavation surface is about 1/3 depth of whole slope . From the curve of whole horizontal displacement of slope surface ,a bumpcan be discovered ; (2) the greatest rebound at the bottom of excavation surface is located% on the center ; (3)when the whole slope is failure , the most settlement of the horizontalsurface behind the slope doesn' t located on the brim of the slope , but at the vicinity of area where the stress is largest ;(4)zone at the bottom of the excavation and some zone under the horizontal surface and behind the slope where its horizontal stress is tensile stress ; (5)the failure of whole slope is caused by the cooperation of shear failure and tensile failure.Having no supporting structure while analyzing deep excavation is the unique style in this paper . It analyzed the deep excavation slope by two-dimensional plane strain method thoroughly aimed at soil itself ?deform property , finding the spatial distribution of stress, displacement and failure soil elements .The obtained conclusions can be used to guide some practical engineering in some sense.