Studies On Compound Soil Nailing With FEM And Its Mechanism

As a foundation pit excavating support technology which is easy and celerity to implement, safe and less cost, soil nailing is getting more and more application to deep excavation construction. However, soil nailing cannot be used in very soft soil or for cases which deformation of the soil nailing has to be strictly limited. To cope with these more difficult situations, compound soil nailing, i.e. a combination of soil nailing with ground anchors, soil-cement mixing piles or mini-piles, is recently developed. However the research on the theory of behavior and mechanism of the structure lags behind the application in the engineering practice. Based on the current studies of the behavior and mechanism of the structure, the paper systematically analyses with the FEM and the elastic-plastic theory in order to meet the need in engineering. And some valuable conclusions are obtained, which can be taken as references in design and construction. The following parts are the work in the paper.(1) Take advantage of software ANSYS, The paper analyses the compound soil nailing with 3D nonlinear FEM. The paper uses Drucker-Prager model as the constitutive model of soil; chooses the Mises Ideal elasto-plastic model which is independent of hydrostatic pressure for the nails and soil-cement mixing piles; takes 8-node hexahedral elements for the element model; holds the face to face contact model for the element on the interface between soil and nails; uses element's "birth and death" for the simulation of staged excavation; given the increase of soil modulus with the depth, An iterative-incremental method is used to solve nonlinear equation.(2) The paper analyses the stress location, displacement of soil, axial forces of nail, displacement of soil-cement mixing piles ofcompound soil nailing with the staged excavation.(3) The paper has a further research on the influence of compound soil nailing behavior in the perspective of the effect of the length of nails, the angle of nails, the stiffness of soil-cement mixing piles, the inserting depth of soil-cement mixing piles, the location of the soft soil.(4) In contrast of the structure behaviors in the staged excavation between the soil nailing and the compound soil nailing and with the analysis of various effecting factors on compound soil nailing, the paper holds a deep analysis of the mechanism's essence of the compound soil nailing.