Deep Foundation Pit Excavation In High-rise Building Three-dimensional Elastic Plastic Finite Element Analysis

Firstly,this paper is aimed at proposing some ideas and methods for some remained im-portant and key problems during the need of practical excavation and the current research ofexcavation. The basic theory of elastic finite element and the basic priciple and the process offinite element for deep excavation analysis is proposed in this paper.Then, 3-D FEM is used to analyse the performance of excavations, and three-dimen-sional elastic and elastic-plastic finite element analysis procedure able to simulate all thestages during construction of practical excavition is programmed. This procedure have thesecharacters.1. It can divide mesh arbitrarily,give the number of element and node automatically.2. It deals with the relationship analysis between stress and strain of soil,finds the fail-ure nodes,then determins the supporting structures.3. Use Microsoft Fortran Powerstation to compile,build, interlink and debug the pro-gram. This improved the efficiency.4. It can analyse the excavation step by step.Finally, throngh some excavation cases in Xi'an, Beijing, Shanghai (which have differentlayers and geological conditions ), the three-dimensional performance of deep excavation wassystematically studied by using this procedure. In this paper, the procedure is used to analysethe stress of soil, horizontal displacement,the settlement of earth surface near the excavationpit,the heave of the excavasion pit bottom,the size of the excavation pit,the effect of the ra-tio of length to width on the horizontal displacement of soil of excavation. and three-dimen-sional effect in the deep excavation. And I draw the conclusion through the elastic and elastic-plastic analysis.1. Excavation has strong fractionated excavation effect,which is related to the depth ofcantilever excavation. From this, We can conclude that the distribution settlement of theearth snrface is triangular.2. Excavation has strong three-dimensional effect,every object of study reach the mini-mum or maximum at the excavation pit corner or centrual sectional plain.3. The size of excavation pit has strong effect on the character of excavation pit. The sizeis more small,the three-dimensional effect is more strong,the limit to the object of study ismore strong.4. With the rising of the ratio of length to width of excavation is improved, the distribu-tion curve on side sectional of the object of research is tending to the result elevation of two-dimensional plain strain.5. The failure of excavation ls mainly shear failure. It occures on the side and corners onthe excavation plt bottom. The failure conclude tensile splitting failure,but it often occureson the border.6. Throngh the analysis of the excavation cases in Xi'an,BelJing and Shanghai,We drawthe conclusion that the depth of vertical excavation cases that in Xi'an district can reach 3-8 meters with no failure. The depth of vertical excavation cases that in Beijing district canreach 3--4 meters with no failure,but when the depth of vertical excavation cases that lnShangHai is l--2m,it wil1 fail. We must excavate soils while sporting them and we must se-lect the appropriate supporting structure.7. The calculated result of elastic theory can accord with the demands. In theory, it lsmore ratlonal to analyse the englneering using elastic--plastic theory. But ca1culated parame-ters ls difficult to determin,and calculation time is long. The calculated throughput is large.So we can take precedence of excavation to use e1astic theory on the condition that it accordedwlth the demands.Having no supporting strcture while analysing deep excavation is the unique style is th1spaper. lt ls aimed at analying the three --dimensional character of soil, flnding the failurenode and three--dlmensional distribution of stress and strain. This have englneering practi-cal slgniflcance.