Study On Bearing And Deformation Behavior Of Batter Pile Under Combined Horizontal And Vertical Load In Collapsible Loess

The foundations of large transmission towers and high-power wind turbines are subjected to both vertical and horizontal loads.Compared with the straight pile,the batter pile has stronger ability to resist the combined horizontal and vertical load,and it has been more and more applied.Because the pile axis of batter pile is inclined,the stress distribution of soil around the pile is non axisymmetric,and the pile-soil interaction is more complex than that of straight pile.When the loess foundation is soaked in water,the bearing capacity of the pile foundation and the pile-soil interaction relationship are obviously affected.Therefore,it is of great significance to study the bearing and deformation characteristics of batter piles in collapsible loess foundation under combined vertical and horizontal loads.Based on the above engineering background,a 1g non collapsible loess pile-soil model test was carried out in the laboratory.The bearing and deformation behaviors of in batter and straight piles under combined vertical and horizontal loads are studied.The results show that the horizontal displacement of the batter pile is larger than that of the straight pile when the pile firstly applies the down load.When the pile is subjected to the combined load of horizontal and downward pressure,the maximum bending moment and shear force of positive batter pile are greater than that of straight pile,and that of straight pile is greater than that of negative batter pile.For the positive batter pile,The larger the inclination angle of positive batter pile,the larger the horizontal displacement of pile top,maximum bending moment and maximum shear force of pile.For the negative batter pile,The larger the inclination angle of pile axis,the smaller the horizontal displacement of pile top,the smaller the maximum bending moment and maximum shear force of pile.Then,the pile-soil model test of 1g immersion collapsible loess was carried out.The purpose of this test is to study the influence of loess collapsibility on the internal force and skin friction of pile under combined horizontal and downward load.The results show that the horizontal displacement increment of positive batter pile is larger than that of straight pile,and that of straight pile is larger than that of negative inclined pile.For straight pile and batter pile,the bending moment,shear force and skin friction of pile increase obviously and the effective length of the pile decreases and the neutral plane of the skin friction of the pile moves downThirdly,the influence of different length diameter ratio and embedded depth of bearing layer on the bearing capacity of the pile in loess is studied by numerical modeling method.For the pile with L / D = 20 / 0.5,the influence of loess on bending moment,shear force,skin friction of pile and pile-soil contact pressure is obvious before and after loess collapsibility.The results show that the vertical compression load increases the bearing capacity of pile.For the same pile length,when the length diameter ratio is small or the length diameter ratio is the same,the bearing capacity of pile foundation with larger embedded depth is higher.The ultimate horizontal bearing capacity of positive batter pile is larger than that of pile,and pile is larger than that of negative batter pile under the combined horizontal and vertical load.After the loess is soaked in water,the bending moment,shear force,skin friction of pile and pile-soil contact pressure increase obviously,and the neutral plane skin friction in front of the pile(ZQ)moves down.Finally,the numerical model of 1×2 batter pile group with cap is established to study the bearing and deformation behavior of batter pile group under different collapsible loads when batter pile group is subjected to the combined vertical and horizontal load.The results show that the horizontal displacement,bending moment,shear force and skin friction of piles increase obviously with the increase of horizontal load when the loess is immersed in water,and for two different kind of piles,the distribution of bending moment and shear force of pile is not equal.