Study On The Influence Of Isolation Membrane On The Negative Friction Resistance Of Loess Pile Foundation Under Pile Load Condition

There is a large area of collapsible loess in western China.In recent years,the country in the western region of the project construction more and more,pile foundation with its unique advantages,has been widely used in foundation treatment.How to avoid the harm of negative friction caused by loess settlement to pile foundation engineering has very important theoretical and practical significance for promoting the safety design of pile foundation engineering.In this paper,on the basis of summarizing the mechanism of negative skin friction resistance of pile foundation,the design of the single pile,indoor model test study of pile when the soil water content is 20% of the loess,and loess on the stack,pile top loads,with or without isolation membrane between pile and soil pile in the soil and pile top settlement,stress and strain of pile and side friction.In addition,ABAQUS numerical analysis software was used to model the indoor model test,and the following research results were obtained by analyzing the situations of changing the material of pile-soil separation membrane and reducing the friction coefficient on the surface of pile body:(1)the mechanism of negative friction resistance of pile foundation is summarized,including the causes of negative friction resistance of pile foundation,distribution law of neutral points,influencing factors and time effect of negative friction resistance of pile foundation;(2)The indoor model test results of single pile show that when there is no separation film between pile and soil,axial force of pile increases gradually along the depth of soil penetration of pile,the neutral point of pile is at the bottom of pile,and all the negative friction resistance is generated on pile side.When there is a separation film between pile and soil,the axial force of pile body increases first and then decreases along the depth of pile penetration,the neutral point of pile rises,and positive friction resistance is generated on pile side;(3)Using numerical analysis software ABAQUS,for simulating the indoor model test,and get no isolation membrane between pile soil,the calculation results and the test compared to the measured data,when the pile pile load respectively 0 kpa,3 kpa,6 kpa,9 kpa,test to calculate the maximum axial stress of pile,respectively,compared with the numerical simulation of the smaller 28.5%,17.7%,16.25%,18.24%,and a few other points,test of axial force of pile is calculated to than calculated by numerical simulation is less than 10%,but the change trend of pile axial force along the pile shaft.This shows that the modeling method is feasible and can be used for further research;(4)Numerical simulation was carried out to change the material of separation membrane between piles and soil and reduce the friction coefficient of pile surface.The results show that by reducing the friction coefficient of pile body,the axial force of pile body and the negative friction resistance of pile body can be reduced,but the neutral point of pile body cannot be changed.The position of neutral point of pile can be improved when the separation membrane is set between pile and soil.