Experimental Study On The Uplift Bearing Characteristics Of Roots Foundation Based On Transparent Soil Technology

With the rapid development of China’s power construction," West-East Electricity Transmission Project" has been continuously promoted,and the UHV power transmission network covering more than half of China has been formed.Due to its own structure,conductor length and height from the ground,the load of UHV transmission tower is much higher than that of High voltage transmission tower.The arrangement form of root has an important influence on its bearing capacity.It is of great significance to explore the pile-soil interaction mechanism under different arrangement forms of root for optimizing the arrangement form of root.Based on the transparent soil and particle image velocimetry(PIV)technology,the vertical pull-up and oblique pull-out tests of equal section piles and nine different types of root foundation are carried out to study the influence of different vertical spacing,length and density of root section along the depth direction on the deformation of soil around the pile.Numerical simulation software is used to analyze the relationship between the bearing capacity of 10 test piles and the displacement of pile top.The main achievements are as follows:(1)It is found that the soil damage is mainly concentrated in the range of 35 mm below the ground surface under the minimum vertical spacing of the shallow root bonds in this paper under the uplift load,which indicates that the stress concentration occurs in the soil in this area,and the soil around the pile is rapidly damaged,which leads to the reduction of the bearing capacity of the test pile;the displacement distribution of the soil around the pile is uniform under the minimum vertical spacing of the deep root bonds,which is equal to it,and the bearing capacity of the test pile is improved High.The results show that the arrangement of the vertical spacing of the root gradually decreases along the depth direction is more conducive to the improvement of its bearing capacity.(2)Under the action of uplift load,the increase of shallow root bond length can increase the displacement influence range and reduce the displacement strength,so as to avoid the stress concentration in the shallow soil,and then improve the bearing capacity of the test pile;while the displacement range and displacement strength of the soil around the deep root bond with the same length are increased,and the bearing capacity is greatly improved.(3)Under the action of uplift load,the increase of the cross-section density of the root bond makes the main displacement influence area extend downward until the root bond of the last layer,forming a mutual connected displacement field.Compared with the original pile type,the increase of the density of the shallow root bond section has a downward extension trend,but the distribution is relatively independent.With the increase of the density of the deep root bond section,the main displacement influence area is completely connected,approximately in a zonal distribution,and the bearing capacity is also greatly improved.(4)Under oblique pull-out load,the displacement mainly occurs in the shallow soil.The reduction of vertical spacing of shallow root bond,the increase of root bond length and the increase of root bond cross-section density can effectively improve the influence range and displacement strength of shallow soil,so as to improve its bearing capacity.On the contrary,the change of the arrangement of the deep root leads to the smaller displacement influence area,which reduces the bearing capacity of the test pile.(5)ABAQUS finite element analysis model is established,which is verified with transparent soil test model test.The simulation experiment shows that the change of root bond load with pile top displacement can be roughly divided into three stages.When the pile top displacement is small,the root bond load increases slowly.With the increase of pile top displacement,the root bond load increases rapidly.When the pile top reaches the ultimate displacement,the root bond load increases slowly and gradually remains unchanged.With the increase of root bond spacing,the bearing capacity of single-layer root bond will be improved,but when the spacing is too large,the bearing capacity of single-layer root bond will be improved The results show that the bearing capacity of the test pile decreases because of the small number of root bonds,and the greater the depth is,the greater the reduction range is;the increase of the length of root bonds has the most obvious effect on the improvement of the bearing capacity of single-layer root bonds,and the greater the depth is,the greater the improvement range is.The increase of root bond density is slightly less than the increase of root bond length on the bearing capacity of single-layer root bond.