Study On Working Mechanism Of Anchor-Pile Retaining Structure System For Deep Foundation Pit

Based on unit design of anchor-pile retaining structure system for a deep foundation pit, the paper uses the finite element software PLAXIS3D to establish three-dimensional models. Through comparing the calculation results of finite element and unit design, analyzing the branch pile internal force and deformation, the axial force distribution of free segment and embedded section of anchor, and the soil settlement and horizontal deformation under different working conditions of excavation, studying the sensitivity of the parameters of the supporting piles and prestressed anchor cables to the whole structure, investigating the influence of different deformation modes of piles on the displacement field of the deep soil, researching on the mechanical properties of the supporting structure, the main conclusions are as follows:1. The current unit design methods are not comprehensive and accurate in predicting the supporting structure of deep foundation pit and complex surrounding environment. The design of foundation pit engineering of major projects should refer to the numerical simulation results and the engineering decision of the unit design should be improved.2. With the excavation, the bending moment, shear force and axial force of the pile are all increasing gradually, and the position of the maximum value appears gradually downward. The maximum shear force and the maximum axial force of each stage always appears at the excavation face of the construction stage. The lowest anchor of the 4 rows of anchor bears the maximum axial force. The position of the maximum axial force of the embedded section changes after the potential surface slide. The deformation of piles is a composite deformation model.3. The surface subsidence curve presents obvious concave shape. The main influence width of the settlement trough is 2 times of the excavation depth range. The variation trend of the surface horizontal displacement curve is consistent with the surface subsidence curve. The value of the surface subsidence and the horizontal displacement of the adjacent pile is not zero. At the end of the excavation, the settlement curves of the soil at different depths of the pit and the horizontal displacement curves of the soil at different distance from the piles show distinct effects on partitioning. The deformation of the deformation transition area is obviously disturbed by the presence of the anchor.4. The change of each parameter can affect the bending moment and deformation, the settlement of the pit and the force of anchor cable. Pile length, pile diameter, pile spacing and anchor cable tension, anchor solid diameter, prestress value and other factors single or combination of changes, will cause the support structure of internal force and deformation of the pit soil deformation.5. The settlement and horizontal displacement of the deep soil under the condition of deformation mode of piles are different, its impact on the division of the partition is also different.6. The maximum displacement of supporting pile is in the position of the neutral point of equal stiffness support structure. The influence of the excavation of the deeper area pit on the shallow area is 2 times the depth of the foundation pit. The horizontal displacement and bending moment of the pile is gradually reduced at the position of the corner of the pit. This project in the east margin of pit row pile distance is relatively large, the pit-in-pit excavation on the influence of east row pile can be ignored.