Numerical Simulation Study On Deformation Of A Foundation Pit In North Changchun City

China's economy has entered a stage of rapid development since the end of 20 th century,the speed of urban construction is also accelerating,urban subways and high-rise buildings and other deep foundation pit projects continue to emerge.In order to reduce the hidden trouble of Deep foundation pit engineering,it is necessary to study its excavation and support.The scope of application of different support structures is different.Since the the1980 s,pile anchor support structure has been widely used.Compared with other supporting structures,pile anchor support can not only make effective use of construction space,but also effectively control formation deformation,so this kind of foundation pit support structure form is also most commonly used in China.The form of pile anchor support involves more basic subjects,which is a comprehensive subject with wide scope and high difficulty.This paper summarizes the previous research results and introduces the principle and type of foundation pit deformation.Combining with a deep foundation pit project in Changchun Beihu area,this paper introduces the monitoring Scheme and foundation pit Support scheme,handles the actual monitoring data,and analyzes the actual deformation of the foundation pit.At the same time,using FLAC3D6.0software to simulate the excavation support steps of foundation Pit,the simulation results of surface subsidence,deep horizontal displacement of pile body and axial force of anchor rod are obtained,and the simulation results are compared with the measured data in the field,and the deformation distribution law of foundation pit soil and pile anchor support structure in excavation process is obtained.The conclusions of the study are as follows:1.When the foundation pit is excavated,there is poor soil pressure on both sides of the support pile,the pile body produces horizontal displacement,the horizontaldisplacement value increases gradually with the excavation,and the maximum horizontal displacement of the support pile is in the upper part of the pile body.In the position of anchor cable,the horizontal displacement value of each point of pile body shows the change of "M" type,the displacement value becomes larger first,then decreases and then becomes larger,which indicates that the displacement value can be effectively controlled by setting anchor cable.2.The horizontal displacement value and sedimentation of soil increase gradually.The horizontal displacement of the soil in each excavation increases first and then decreases,and the increase of the horizontal displacement value of each anchor soil will be controlled.The settlement value decreases gradually with the distance from the top of the slope.The bottom of the foundation Pit has a bulge,from the center of the bottom of the foundation pit along the perimeter by large smaller.3.Anchor cable axial force for tension,from the upper to lower axial force increased,each row of Anchor cable axial force is the middle large,the two ends are small.From the part near the free segment to the Anchorage section direction from large to small.4.The monitoring results show that the horizontal displacement value and settlement of the western soil are greater than the east side,which may be due to the new board room on the west side and the load construction materials caused by excessive pressure,coupled with the construction speed is too fast,the west side near the excavation of the empty surface of the road there is a crack can be supported.5.The measured value and the simulated value are larger than the measured value,which indicates that the factors considered in the actual simulation are slightly deficient,and the accuracy of the parameters and external factors can lead to errors in the simulation results.The change trend of the two is generally consistent,which shows that it is feasible to simulate the excavation deformation of foundation pit with FLAC3 D to a certain extent.Comparing the monitoring results and simulation results,the deformation of foundation pit is controlled within the range of standard allowable value,which shows that the design of pile anchor support is reasonable,the establishment of the modeland the selection of parameters are roughly correct,so as to provide reference for the optimal support design of foundation pit similar in this area.