Research On Spatial Theory Of Stabilizing Micropile Groups In Slope Engineering

Micropile has been widely used in landslide treatment because of a lot of merits such as its light structure, easy and quick construction as well as its safety and flexibility with comparison with the traditional stabilizing support structure, and some favorable results have been achieved in project practice. However, the present analysis theories are mostly based on the plane strain hypothesis to analyze the design and calculation of the structure, while they neglect the interaction of the pile-soil between the structure and the slide body. In light of this, based on the common3×3stabilizing micropiles with roof plate composite structure, the analytical calculation method is derived by considering the features of the three-dimensional structure. The main contents and research results are as follows:1) On the basis of the three-dimensional features of stabilizing micropiles with roof plate composite structure, a new analytical calculation model is proposed, that is to say, the part above the slip surface is regarded as spatial frame and the part below the slip surface is elastic foundation beam.2) With the consideration of the spatial effect of composite structure, mechanical analysis of spatial frame above the slip surface is divided into in-plane calculation and out-of-plane calculation. Calculation formula for distribution coefficients of out-of-plane landslide thrust is derived through the theoretical analysis and its rationality is validated by the numeric simulation method. Then, some influencing factors of the distribution coefficients of out-of-plane landslide thrust have been discussed. The results show that load bore by the middle column along the landslide trend is larger than that of the fringe column, and the distribution coefficients of the middle column, whose interval is from the1/3to1, decrease with the increase of the out-of-plane internal spacing of composite structure.3) The in-plane distribution of the spatial frame affected by landslide thrust is researched by the numeric simulation method. Under the triangle and rectangle distribution modes of the slide thrust, the fitting formula of force distribution coefficients of the in-plane micropiles is given and sensitivity of every factor has been analyzed at the same time.4) The calculation formula of internal force and deformation at any section of spatial frame has been deduced by analyzing the structure above the slide surface through the analytical method of structural mechanics.5) The allowable stress method and limit state method are respectively used for the composite structure analysis. And the calculation formula of extreme point of internal force along the pile has been derived and the ultimate bearing capacity of the composite structure is back calculated. Taking the engineering practice as the example, this paper concludes a rule that four main factors:out-of-plane internal spacing a, micropile diameter d, soil modulus Es and pile length of loading segment L have influences on ultimate bearing capacity of the composite structure.In brief, on the basis of the three-dimensional features of stabilizing micropiles with roof plate composite structure, this paper deduces the calculation analysis method of stabilizing micropile groups with the consideration of the landslide thrust spatial distribution and transmission. The research results are helpful for the actual design of stabilizing micropiles composite structure and can provide theoretical guidance and references for practical projects.