Experimental Study On The Effect Of Horizontal Load On The Transfer Function Of Pile Foundation In Collapsible Loess Area

The northwestern region is the main area of loess distribution in China,of which collapsible loess accounts for more than 70% of the total area of loess in the northwestern region.With the country's great emphasis on the economic development of the northwestern region,road network planning and infrastructure construction are economic development In the first step,due to the special geological structure in the northwest region,pile foundations are increasingly used in infrastructure construction.In recent years,as the construction of large-span curve bridges and UHV transmission towers has become increasingly widespread,pile foundations will not only be subjected to vertical loads,but also to horizontal loads under the action of centrifugal force,locomotive braking force,traction force,etc.Summarizing the studies of scholars at home and abroad,the study of the vertical bearing characteristics of single piles and the relative displacement of piles and soils under the action of horizontal loads is still lacking.More scholars are required to conduct research in this field.Based on the above reasons,this paper carried out an experimental study on the effects of horizontal loads on the vertical bearing characteristics and ultimate bearing capacity of pile foundations in collapsible loess areas under different load conditions and different soil environmental conditions around the pile.The main conclusions are as follows:(1)Under the vertical load of the pile top,the axial force of the pile gradually decreases with the burial depth.When approaching the bottom of the pile,the axial force of the pile tends to be zero.When the vertical load of pile top is small,the axial force decreases rapidly along the buried depth,and the slope of the curve is large.With the increase of vertical load of pile top,the rate of axial force decreasing along the buried depth gradually slows down,and the slope of the curve is smaller.(2)Under the two conditions of immersed and non-immersed,with the increase of horizontal load and water content,the angle of pile top increased correspondingly,but the angle of pile top increased more rapidly;under the same horizontal load,with the increase of the vertical load of the pile the top turning angles are gradually reduced.(3)Under both the flooded and unimmersed conditions,the pile top settlement gradually increased with the increase of the vertical load,but the submerged group settled faster;when the pile top acts on the same vertical load,under the two submerged and submerged conditions,the single pile top The settlement gradually increases with increasing horizontal load.After analysis and comparison,it is concluded that the existence of horizontal load reduces the vertical ultimate bearing capacity of a single pile.(4)Under the two conditions of immersed and unimmersed,with the increase of horizontal load,the bending moment of the pile body first increases to the maximum positivebending moment along the pile depth,then gradually decreases to zero,and continues to increase with the depth The maximum negative bending moment then gradually decreases to zero;under flooding conditions,the position of the maximum positive bending moment of the pile body under different vertical loads moves down,and the position of the maximum negative bending moment of the pile body remains basically unchanged,compared to In the non-immersed condition,the negative bending moment of the pile body under the immersed condition decreases as the pile depth decreases.(5)Under the same horizontal load,the maximum positive bending moment of the pile body is significantly larger than the maximum negative bending moment of the pile body in the immersed and non-immersed groups,indicating the effect of horizontal load on the pile body bending moment It is mainly distributed in the middle and upper part of the pile body.The bending moment of the single pile is mainly borne by the upper half of the pile foundation.This is to strengthen the reinforcement ratio of the upper end of the pile body against horizontal loads when designing the reinforcement of the large-diameter cast-in-place single pile foundation.,Is of great significance to engineering design and construction.(6)At the same pile burial depth,the relative displacement of the pile and soil gradually increases with the increase of the horizontal load under the two conditions of immersed and unimmersed;under the same horizontal load,the relative displacement of the pile and soil is basically along the pile burial depth It remains unchanged;the rate of increase in the relative displacement of the pile and soil is reduced by 20% when compared with the unimmersed condition.(7)By analyzing the horizontal load-displacement relationship curve and horizontal load-displacement gradient relationship curve of single pile under immersed and non-immersed conditions,the horizontal critical load and horizontal limit of single pile under different vertical loads are obtained Characteristic values of load and horizontal load of single pile.