Study On Reinforcement Mechanism And Calculation Method Of Micropile Group With Roof Plate In Soil Slopes

Micropile group with roof plate is a new type of anti-slide structure,its beam reinforcement as framework and protection of pouring cement mortar beam bars around,and then connect with reinforced concrete slab at the top.This type of micropile has the characteristics of small pile diameter,large aspect ratio,and low bending rigidity.Because of the advantages of quick construction,it is widely used in engineering practice.But the calculation and analysis theory of this new type of micropile is not perfect.Based on the subgrade slope engineering of Dali to Ruili railway in Yunnan,theoretical analysis,model test and numerical simulation are adopted to study the mechanism and calculation method of reinforced soil slope with this type of micropile.The main research results are as follows:(1)This paper analyzes the action mechanism of single pile in strengthening soil.On this basis,the mechanism of the consolidation of side slope by micropile group with roof plate is revealed.The influence of main factors on the failure behavior of single pile and pile group is confirmed.(2)Considering the unstable slip surface of slope is inclined,the maximum pile spacing between the micropile groups and the maximum pile spacing in the group are deduced based on soil arching effect.For the group spacing,a new analysis method is proposed in this paper.The compression region at the intersection of adjacent soil arches is assumed to be trapezoid,and the strength condition of soil arch compression zone and mid span vault is taken as the basis of judgment.(3)Through laboratory model test,it is concluded that the horizontal ultimate bearing capacity of the pile-soil structure is improved with the increase of the internal spacing of the micropiles within a certain range.Vertical load on pile cap can increase horizontal ultimate bearing capacity of the micropile group.With the increase of the vertical load,the increment of the bearing capacity also increases.(4)Considering the vertical load on pile cap,a new method for calculating the internal forces of the piles in the unit micropile group is proposed based on the coordinated deformation of the micropile group with roof plate.According to its mechanical features,the structure can be analyzed by dividing it into the loaded segment and anchored segment in light of the location of potential slip surface.The landslide thrust and soil resistance of the loaded segment is assumed to be parabolic,and the soil resistance of the anchored segment is calculated using the two parameter form of the m method.First,the initial parameter equation of the power series method is obtained,and then the internal forces and displacements of each pile are obtained according to the continuity condition of each pile at the slip surface and the displacement coordination condition of each row of piles at the top of the pile(5)Combined with the engineering practice,the displacement and bending moment of the micropile group with roof plat are calculated by using the proposed method.The calculated results are in good agreement with the numerical simulation results,and it is pointed out that the additional moment effect of the micropile under the vertical load on pile cap is obvious.In this paper,the results of the calculation and analysis of the soil slope of the micropile group with roof plate can provide guidance and reference for practical engineering design,and have important theoretical and engineering significance.