The Installation Effect And Uplift Capacity Of Helical Anchors In Dense Sand

As an important link in the construction of the "global energy Internet" and the "the Belt and Road",high-voltage transmission lines are closely related to our production and life.Through continuous development,their importance is increasing.As a new type of foundation,screw anchor foundation has the advantages of convenient installation,rapid construction and rapid bearing.It can bear large uplift and compression loads.It has been applied in both land and marine environments.Compared with the traditional foundation,the spiral anchor foundation has great potential.This foundation is gradually popularized and applied in the transmission line engineering in China.In order to better apply this new type of foundation,it is necessary to more accurately understand the influence of its geometric characteristics and installation methods on the uplift bearing characteristics.However,there are relatively few studies on the installation effect of screw anchors,so it is necessary to conduct more in-depth research on the installation effect of screw anchors and its impact.In this paper,the discrete element method（DEM）is used to simulate the installation and uplift of screw anchors in dense sand.（1）To verify the accuracy of the numerical method used in this paper,a 1:1 spiral anchor model and soil model are established,which are similar to Hiroshi Nagai’s indoor model test.The diameter of the spiral anchor plate is 97.2mm and the buried depth is 500 mm.The uplift load displacement curve and the ultimate uplift bearing capacity are obtained.The trend of load displacement curve is the same,and the difference of ultimate uplift capacity is 3.4%,which verifies the validity and feasibility of the discrete element model established in this paper.（2）In view of the disturbance caused by the installation of screw anchor,the influence of installation effect on the deformation characteristics of soil is analyzed,and 15 groups of models with anchor disc diameter of 100 mm and different buried depth are established for calculation.The results show that the soil around the screw anchor is compressed and sheared,and the screw anchor and soil have complex coupling effect.With the increase of the penetration depth,the radius of the disturbed area of the soil decreases gradually,and the disturbed area will continue to increase.After the installation,the overall disturbed area is an inverted triangle.With the increase of the number of anchor plates,the disturbance times of screw anchors to soil increase,and the displacement of soil increases.The displacement of soil mass increases with the decrease of disc spacing.（3）In view of the influence of the geometric size of the screw anchor on the installation disturbance and the installation effect on the uplift bearing capacity of the screw anchor,a numerical model is established for calculation and analysis by changing the disc diameter and buried depth ratio.At the same time,it is compared with the embedded（no installation disturbance）situation,including 36 groups of models.By comparing the load displacement curve,ultimate bearing capacity,failure mode and critical depth of embedment and penetration,the installation disturbance and its influence are analyzed.The results show that the ultimate uplift bearing capacity of the penetration installation method is smaller than that of the embedded method,which may be caused by the reduction of soil compactness and the destruction of the original structure of the soil after the soil is disturbed.And with the increase of buried depth and disc diameter,the difference of ultimate bearing capacity between the two installation methods gradually increases,that is,the greater the buried depth and disc diameter,the greater the degree of disturbance caused by installation,and the more the bearing capacity decreases.Under the two installation modes,the critical buried depth of single anchor and the sharing efficiency of double anchors have little difference.In this paper,the installation effect of screw anchor foundation with different geometric dimensions and its influence on the uplift bearing characteristics are studied by numerical simulation,and the effects of buried depth ratio,anchor plate number and anchor plate spacing ratio on the uplift bearing characteristics of screw anchor are analyzed,which provides a certain basis for more accurate calculation of the uplift bearing capacity of screw anchor foundation.