Mechanical Properties Analysis On Frame Prestressed Anchor Micro Steel Tube Pile Combined Retaining Structure Of Deep Foundation Pit

Frame prestressed anchor micro steel tude pile is a kind of combined retianing structure which is used to solve the problem of deep foundation pit support in the construction of deep foundation pit in the narrow construction site and the backfill unconsolidated soil and loose soil area.In the new structure,the anchoring technology,the self-drilling technology and the pressure grouting technology are combined together;the good anchoring effect of anchor,the characteristics that the soil is compacted and improved under the action of steel pipe self-drilling and pressure grouting,and the performance that the frame prestressed anchor and the micro steel pipe pile cooperatively work are combined together in order to comprehensively control the existing problems in deep foundation pit engineering in areas with complicated geological conditions.In this paper,the theoretical analysis and numerical simulation are used to analyze the supporting characteristics of frame prestressed anchor micro steel tube pile combined retaining structure.The concrete research contents and conclusions are as follows:(1)The structure construction,construction method and construction procedure of the frame prestressed anchor micro steel tube pile combined retaining structure are introduced in detail,and its working mechanism is discussed in depth.According to the working mode of the supporting structure,the working mechanism can be divided into the anchoring mechanism of the frame prestressed anchor,the reinforcement and support mechanism of the self-drilling micro steel tube pile and the unloading mechanism of the frame prestressed anchor micro steel tube pile.(2)Considering the characteristics of the construction and operation phases of the frame prestressed anchors,based on the theory of Winkler elastic foundation beam,the calculation model of the interaction between the frame prestressed anchor micro steel tube pile and the soil in tension period and normal working stage are established.Then the deformation and internal force of the frame prestressed anchor micro steel tube pile combined retaining structure are calculated by the displacement method and the finite difference method.The example analysis shows that the difference between the displacement and bending moment of the three row micro pipe piles is small,and the maximum bending moment appears at the top of the pile.The closer the internal force value of the frame column is to the crown beam,the more significant the change of the frame column is at the working stage.(3)By using numerical simulation software ADINA,the two-dimensional finite element model of excavation and support of deep foundation pit is established.The supporting characteristics of the frame prestressed anchor micro steel tube pile combined retaining structure at different excavation times are obtained.The advantages of the combined retaining structure are verified by comparing with the supporting characteristics of the pile-anchor retaining structure under the same conditions.Furthermore,the effects of grouting radius,the support depth ratio of the upper and lower structure and the row number of micro steel pipe pile had on the supporting characteristics of frame prestressed anchor micro steel pipe pile are studied.The results show that:(1)The displacement of soil in foundation pit and the internal force of retaining structure are decreased with the increase of grouting radius.(2)The support depth ratio of the upper and lower structure has little effect on the vertical displacement of soil in foundation pit,but it has a great influence on the horizontal displacement of soil in foundation pit and the internal force of the supporting structure.(3)The mechanical properties of combined retaining structure with three rows of piles is better than that with two rows of piles in terms of the cost and support effect.(4)The comparison between the theoretical value and the conventional theoretical value without considering the implicated effect and the numerical simulation results shows that: the theoretical method proposed in the paper is closer to the simulated value than the conventional method that does not consider the implicated effect.And the variation discipline is basically consistent,which verifies the rationality of the theoretical calculation model and analysis method,and can provide theoretical basis and reference for the analysis and design of the deep foundation pit combined support structure.