Behaviour Of Laterally-loaded Single Piles With Stepped Variable Cross Section

In transmission line engineering,pile foundation is a common type of foundation.In order to ensure the stability of transmission line foundation under horizontal load,the selection and optimization of pile foundation is particularly important.Many scholars continue to explore and innovate the types of pile foundation,and variable section pile is one of them.At present,the research on variable section pile is mainly through field test,numerical simulation and theoretical research,mainly focusing on reducing the settlement of pile foundation.The results are scattered,and the research on the influencing factors of horizontal bearing of foundation is less.In this paper,the influence factors of horizontal bearing behavior of variable section pile are studied by numerical simulation and theoretical research1.FLAC3D software is used to establish the numerical calculation model of variable cross-section single pile,and the horizontal bearing capacity of variable cross-section single pile is analyzed.The results show that the soil pressure on the side of pile is mainly concentrated in the soil above the variable cross-section position,and has little influence on the soil at other positions.At the initial stage of loading,the plastic zone is mainly concentrated at the pile top and the position of variable section.With the increase of load,the plastic zone gradually develops along the pile foundation,and finally forms a through zone above the position of variable section.The expanding section bears most of the load.2.Increasing the variable diameter ratio can significantly improve the horizontal bearing capacity of pile foundation.When the length of expanding section and the variable diameter ratio are different,the characteristic value of the unit volume horizontal bearing capacity of variable section pile may reach the same,and the reduction rate of bending moment under the displacement of variable section pile is higher than that of equal section pile.The ratio of the length of expanding section to the length of pile is 0.4 ～ 0.5,and the range of diameter changing ratio is 0.8 ～ 0.9.When the pile length reaches a certain value,the ratio of the distance from the maximum bending moment to the pile top to the pile length will not change.The position of the maximum moment point increases with the increase of the elastic modulus of soil,and has no effect on the position of the maximum moment point of pile.The effect of cohesion strength and internal friction angle is mainly on the load displacement curve,but has no effect on the position of the maximum moment point.When the thickness of the hard shell is less than the length of the expanding section,the curve of the characteristic value of the horizontal bearing capacity changes slowly,and when it is greater than the length of the expanding section,it changes faster.The position of the rotation center of the pile is below the variable section,and there is a critical value for the influence of the thickness of the hard shell on the position of the rotation center.3.The bending moment calculation results of variable cross-section pile derived from elastic pile theory are in good agreement with the numerical simulation results and field test results.The rigid pile theory calculation results are larger than the previous three results.The calculation accuracy of elastic pile theory is high,so it can be used for variable cross-section pile calculation.When calculating the vertical resistance coefficient of foundation,the calculation of pile length is too large,which leads to the large moment difference between the upper and lower parts of the variable section position.Therefore,it is more appropriate to calculate the length of the expanding section.