The Research On Design Method Of Anchor Pile In Deep Foundation Pit Supporting Structure In The Sand And Gravel Field

In recent years, anchor piles are used more and more widely in the engineering of deep foundation pits because of its unique capability of force and anti-deforming at sandy site in Chengdu area. Most scholars have focused their research on the working condition and construction measures of the engineering, but the research on the theory of retaining and protecting design for excavation pit, specially on the calculation model and its applicability, are less. A large number of engineering practice shows that the model the bylaw of Technical specification for retaining and protection of building foundation excavation provides is different from the actual situation, which leads to difference between the internal force, deformation of the support structure and practical values monitored from situation.Starting with the basic theory, this paper has an analysis of the applicability of the design method the active bylaw provides; Then combining with the analysis of some projects’ geologic surveys, proposals of design and monitoring, this paper puts forward the existent problems on the choice of values of deign parameters, measures of monitoring; After that, two typical examples are elected to find the difference between the actual results of monitoring and the one of design, the reason why the difference exists, and controls parameters by making a contrast between them. Finally,2D finite element model that is fit for the actual situation is built up to fully analyze on the influence the soil strength parameters, construction condition and embedded depth of piles on the deformation and internal force of the piles.After the research above, some conclusions for similar retaining structure of deep foundation pit at sandy sites are made as follows:1. The active bylaw regards the structure as an plane problem, that is, space effect isn’t considered into the bylaw, also the structure design is on the basis of most unfavorable condition, which leads to a conservative and uneconomical design.2. The calculation model of deformation, provided by the active bylaw, is general to prop-structure for deep foundation pits at sandy site, while the calculation results of moments and bar arrangement are conservative at the same time.3. As the pressure state, due to deformation, isn’t taken in to account during the calculation, the earth pressure back of pile should be zoom out while the one in front of pile should be zoom in in the future design.4. The intensity parameter has the biggest influence on the deformation and internal force of the piles at sandy site, specially at some sites that sandy layer dominates, so when a design is going to be made or a project treated, the enhancement of sand intensity should be taken as the main objective, similarly, to reduce project cost, the enhancement of the intensity due to dewatering can be also considered.5. It is beneficial to the deformation of piles and the distribution of the bending moment if the anchor lines are set after a certain super digging depth.6. The different embedded depth has little influence on the safety factor of the stability, while the moment of pile significantly increases when the embedded depth is longer, and the checking method provided by bylaw is practicable at sandy sites, besides the detailing requirement that the embedded depth should be longer more than0.2H at sandy sites is beneficial to a certain degree.7. Compared to the influence of different embedded depth on the deformation, internal force of the piles and the plastic damage area of soil, the model of bolting can be adopted to design the anchor piles.