Analysis On Deformation Monitoring Of Deep Foundation Pit With Pile-anchor Support

In view of the increasingly prominent problems of deep foundation pit slope(deformation,swelling and collapse of foundation pit slope),a deep foundation pit support project in Xi’an is taken as the research object,with the help of collecting data and on-site monitoring,the design,monitoring analysis,numerical simulation analysis and optimization design of pile-anchor support for deep foundation pit are carried out,and some valuable understandings and conclusions are obtained:(1)taking an example of deep foundation pit as the research object,according to the engineering survey and site conditions of the research area,this paper analyzes the characteristics and difficulties of deep foundation pit support,compares and selects the schemes,and formulates the support form of bored pile +prestressed anchor cable for deep foundation pit.Then,the model of pile-anchor support is established,and the relevant parameters of pile-anchor support are selected.After checking and calculating the stability against overturning,the stability of the whole.(2)before the construction of the deep foundation pit,the monitoring points of the displacement and deformation of the pile body were set up by pre-burying the measuring inclined pipe in the pile hole,in order to monitor the horizontal displacement of Pile Top,vertical displacement of pile top and deep displacement of pile body during the construction of pile anchor retaining structure in deep foundation pit,the settlement monitoring points are set at 5 m and 10 m from the side of deep foundation pit,to monitor the surface settlement of the side of the deep foundation pit during the construction process,and finally obtain the deformation monitoring values of the pile-anchor retaining structure of the deep foundation pit and the settlement monitoring values of the side of the deep foundation pit,the conclusions are as follows: The horizontal displacement of pile top increases with the increase of excavation depth,but the horizontal displacement of pile top has different degree rebound after adding each layer of anchor cable,which proves that anchor cable restrains the horizontal displacement of Pile Top;When the first excavation reaches 3.3 m,the deep displacement of the pile body is large at the top and small at the bottom,the deep horizontal displacement of the piles up to 13.1 M is in the form of "Crescent",and the anchorage cable has a good limiting effect on the deformation of the retaining piles.The maximum horizontal displacement of the row piles is 8.76 mm In the process of earth excavation of deep foundation pit,when the excavation depth is relatively shallow,the settlement takes the form of "funnel-shaped" settlement deformation with "large pile top and small distance away",and when the excavation depth is deeper and deeper,the surface settlement is larger at a certain distance from the pit edge,however,the settlement at both ends of the pit is small,and the total settlement is parabola.The maximum surface settlement of the pit is 6.56 mm.It is found that the deformation of retaining pile and the surface settlement of deep foundation pit need to be further optimized.(3)using FLAC3 D finite element software to carry on the numerical simulation analysis and the optimized design to the original design plan,first established the pile anchor support structure numerical simulation model,has determined the model correlation parameter,using FLAC3 D finite element software to simulate two parameters of pile diameter and embedded depth by single factor test,the horizontal displacement curves of Pile Top,deep displacement curves of pile body and settlement curves of deep foundation pit under different working conditions are obtained.By comparing the monitoring data,it is found that the deformation settlement value of the original design scheme is similar to that of the actual monitoring.Then it is found that the change of pile diameter has more influence on the deformation and settlement of deep foundation pit than the change of embedded depth of pile body,and the optimum design scheme is obtained: The optimum diameter of pile is 1.2 m,the optimal embedded depth of retaining pile is 6m(about 0.46 H,h is 13.10m).The optimization results show that compared with the original design scheme,the maximum horizontal displacement of pile top is reduced by 2.03 mm,the maximum deep displacement of pile body is reduced by 2.17 mm,and the maximum settlement of pit edge is reduced by 1.87 mm.