Test And Research On Force And Deformation Of Anchor-Stake Foundation Pit Support

Foundation pit engineering has always been a hot spot for geotechnical engineering.The understanding and research on the deformation and stress characteristics of the foundation pit support system are of great significance to the theory and practice of foundation pit engineering.Based on the actual measurement of the project,this paper analyzes the deformation and force of the foundation pit and supporting structure during the excavation of the complex plane shape foundation pit anchored piles on the soft soil site,in order to further understand the engineering work characteristics of the anchored pile support system.The main contents and conclusions of the study are as follows:(1)Through the actual foundation pit engineering test analysis,the spatial effect is obvious for the foundation pit with complex plane shape.The influence of space effect on the foundation pit and supporting structure should be considered in the design,and the supporting structure should be properly adjusted in different parts to avoid safety hazards or too conservative.(2)Deformation characteristics of foundation pit soil and supporting piles are obtained through field measurement data analysis.The maximum horizontal deformation of the soil on the side wall of the foundation pit(except the negative angle)is about 0.17%~0.26% of the excavation depth of the foundation pit.The maximum horizontal displacement of the pile top is about 0.25%~0.54% of the excavation depth of the foundation pit.The maximum horizontal displacement of the pile body is about0.10%~0.57% of the excavation depth of the foundation pit.(3)Analyze the measured data of the anchor cable axial force to obtain the change law of the anchor cable axial force with various working conditions.With the excavation of the foundation pit,the axial force of the anchor cable is gradually increased,but with the action of each layer of anchor cables,the axial force increasing rate is gradually reduced until it is basically stable,which is different from the assumption of the calculation of the multi-support fulcrum beam method.According to the measured results,the design value of the anchor cable axial force can be increased by about 15%for the local unfavorable position(such as the positive angle,the middle position of the long side of the foundation pit,etc.),and other parts can be designed according to the design value of 80%~90% of the axial force calculation value.(4)Based on the analysis of the measured data,the theoretical analysis and calculation of the influencing factors of the supporting forces and deformation of the anchor-pull pile foundation pit are carried out,and the stiffness of the crown beam can reflect the influence of the space effect of the foundation pit to to some extent,but the current crown beam stiffness calculation formula is only applicable to the case where the two ends are negative angles,and the positive angle is not considered.The calculation of anchor cable stiffness is unreasonable.The influence of cable length reflected by it does not conform to the theory and practice,and does not consider the influence of soil properties and anchor cable axial force.Computational analysis shows that the prestressing degree of the anchor cable,the stiffness of the anchor cable,the stiffness of the crown beam have a great influence on the displacement of the pile top,the maximum horizontal displacement of the pile body,the bending moment of the pile body and the axial force of the anchor cable,but the overall foundation pit stability effects are not considered.