| 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 soil-cement mixing piles or mini pile, is recently developed. However the research on theory of behavior and mechanism of 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 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. Taken advantage of software GeoFBA, The paper analyses the compound soil nailing with nonlinear FEM. The paper use Drucker-Prager model as the constitutive model of soil, use Pole module as the model of soil nails, use Girder module as the model of soil-cement mixing piles, use Goodman module as the model of interface, an iterative-increment method is used to solve nonlinear equation.2. The paper has a further research on the influence of compound soil nailing behavior in the perspective and the axial strength of the soil nails of the effect of the stiffness of soil, the stiffness of soil-cement mixing piles, the width of soil-cement mixing piles, the length of nails, the angle of nails. The paper also has a research on the influence of compound soil nailing behavior in the perspective of silt and hardpan of the effect of the width of soil-cement mixing piles.3.With the analysis of various effecting factors on compound soil nailing, the paper holds a analysis of the mechanism's essence of the compound soil nailing.
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