| With the development of urban construction and the expanding of undergroundspace,the foundation pit of structures is deeper and deeper.In the deep foundation pittimbering engineering,foundation pit often collapses and the structures and roads aroundcollapse or crack for the unreasonable design,improper construction or naturaldisaster,which directly influence the construction progress and the engineering cost ofstructures,even endanger people’s life and property security.Therefore,the research ondeep foundation pit timbering engineering theory is urgent and necessary.In deep foundation pit engineering, the foundation pit plane shapes,excavationdepth,surrounding environment,load conditions,and exposure time length,all of theseforce effects the force and displacement greatly.At present,the design principle of the foundation pit engineering construction islimit state design method based on the probability theory,according to the characteristicsof all kinds of structures and application requirements,getting the limit state equationand specific limits as the basis of structure design. With the the failure probability orreliable index of structure to measure the structure reliability,use the probability theoryto construct a relationship between the structural limit state equation and the structurereliability.High-rise building become higher today,and the deep foundation pit timberingengineering demands exact displacement control.The design principle of foundation pitengineering construction is developing from"strength failure limit state"to"displacementcontrol limit state"."Displacement control limit state"takes strain and deformation as thebest indicators of potential damage,and designs the structure as a certain limit stateunder a given strain and deformation.However,calculation theory and methodof"displacement control limit state"is not perfect,the indoor model test is limited by thetest apparatus,research methods and operating method of the restrictions,therefore thereliability of the test result is not so good.Thus,the calculation theory and methodof"displacement control limit state"have important theoretical and practical significance.This paper employs ABAQUS software to take a numerical simulation of the deepfoundation pit indoor model test and its actual project considering of the spacegeometry size influence.Conclusions are got as below:1.The effecting rule to the underground continuous wall coping displacement bythe foundation pit excavation width and the distance from the underground continuouswall to the outside fixed boundary according to the numerical simulation of the deep foundation pit considering of the space geometry size influence.2. The comprehensive analysis and calculation of the relative size of deepfoundation pit model are done in this paper. During the indoor model test process thereare two aspects needed to be considered:firstly,to assure the indoor test model not toobig which will increase the test difficult expenditure and waste resources；secondly，toassure the model deformation can be observed clearly in order to analyzing thetransformation condition more exactly in the indoor model test.According to the twocomparison and analyze， the optimum model size proportion is got asB1/L1=1.5,B2/L2=3.0.3. A numeral simulation of the actual continuous underground wall projectconsidering the space geometry size influence is done.The conclusions are got as belowfrom the analyze:(1)With the excavation width of the model reducing,the horizontal displacementof the wall decrease,and with the excavation width decreasing the wall’s horizontaldisplacement increment increases,which could be confirmed by the numericalsimulation of the indoor model test.(2)the biggest principal stress is focused on the top and bottom of thewall,relatively small in the middle of the wall,but is greater than the soil.(3)wall deformation is mainly the horizontal displacement, the excavation surfacedeformation is mainly upheaval,and the outside excavation surface deformation of soilis mainly the precipitation.(4) The following conclusions can be got from the analysis of foundation-pitbottom curve: the uplift is the biggest at the central axis,and decreases with the distanceto the central axis,and tends to be0up to the underground continuous wall.But the reducing rate by the increase of the distance is not constant: at the beginning,the uplift deformation reducing rate is very small;about to the3/5,a mutation will takeplace,the reducing rate will increase sharply；up to the4/5, another mutation will takeplace, the reducing rate will increase more sharply and continues to undergroundcontinuous wall.(5)The following conclusions can be got from the analysis of the soil surfaceprecipitation curves:at the underground continuous wall coping,the precipitationdisplacement value is the minimum,close to0;from the wall coping to theoutside,firstly the precipitation increase sharply,to the maximum at about2m; and thenoscillates within the scope of3m~8m,finally tends to be stable. |
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