Study On The Mechanical Deformation Characteristic And Stability Of Deep Foundation With Pile-Anchor Structure

The pile-anchor reinforcement structure is a new type of slip resisting structure and was applied developed from 80s, 20 century, which is widely used in the reinforcement of deep foundation and slope. But in recently, the studies on the couple mechanical characteristic of pile-anchor reinforcement structure, its numerical realization method and foundation stability influential factors are still not enough.According to the former material, theoretical analysis, insitu test, numerical simulation technique and engineering monitoring, the reinforcement effect of pile-anchor for foundation, the interaction between pile-anchor structure and soil, the effect of pile-anchor reinforcement parameters to the foundation stability, the numerical method of foundation stability calculation and the interaction between pile structure and anchor structure are studied in the present paper, which will give guidance for the theoretical application and real engineering.The interaction mechanism of the pile-soil and cable-soil is analyzed, the interaction model of pile-anchor structure and soil is founded to study the deformation condition and failure modes. The pile-anchor numerical calculation element is built according to the interaction between pile-anchor and soil, which will give the foundation for the further numerical calculation.According to insitu monitoring, the fitting models for limit anchoring force with surrounding pressure, and the anchoring force with the cable length are built, then the relationship between the ancoring force with surrounding pressure and cable length can be quantitilized analyzed, which shows that, with the increase of loading, displacement of cable increases gradually in the nonlinear way; when the loading is small, the load is mainly resisted by the cohesion and friction of the interface; with the slip of cable increases, the cohesion of the interface decreases rapidly, while the friction decreases as well for the grain been milled; the distribution of the cable axial force shows the maximum magnitude at the cable and decreases along the cable shaft; with the increase of the tensile displacement, the anchoring force of the cable becoming gradually large; with the increase of the surrounding stress, the failure load of the cable increases gradually, whose relationship meets the exponential equation.The differences between limit equilibrium method and shear strength reduction method are compared, in which the mechanism and limitation of the limit equilibrium method are analyzed, while the characteristic and implementation procedure of the shear strength reduction method is studied, which validates the strength reduction method.The FLAC3D numerical simulation method based on thhe strength reduction method is used to study the distribution of foundation slip plane and their influential factors, which show that with the increase of the cohesion, the slip plane moves from shallow part of foundation to the inter part of foundation; the upper part of the slip plane moves farther to the vertex of foundation; with the increase of internal friction angle, the failure mode of the foundation changes from deep slippage to shallow slippage, the upper part of the slip plane moves closer to the vertex of the foundation.According to the characteristic of pile element and cable element, the join nodes of the two elements are deleted, then the new connection between them is built, the interaction between them in the FLAC3D is numerical realized; the influencing factors for pile-anchor structure are analyze, and fitting model for the cable length and safety factor with different cable inclination is studied, which shows that the relationship between foundation safety factor F and cable length can be described by linear equation with high coefficient; with the increase of cable length, the slip plane of foundation changes from shallow slip plane to the deep slip plane;The interaction effect of pile and cable is analyzed as well as their stress and deformation transformation characteristic, which show that, the reinforcement pile mainly resists the compression in the axial direction; the distribution of the compression shows the trend of first increases then decreases along the pile shaft; with the increase of cable length, the compression along the pile shaft decreases gradually; during the excavation procedure, the mode for the axial force of reinforcement pile changes from tensile to compressive.According to the monitoring and numerical calculation results for a typical engineering, the validations for the numerical method and numerical calculation results are proved.