Study On Bearing Capacity Of Single Pile In Unsaturated Loess Under Infiltration And Humidification

Loess is a special kind of soil formed under arid and semi-arid climatic conditions.It has uniform soil texture,developed pores,and is rich in soluble salts.It is prone to large areas of collapsibility when exposed to water.Both natural phenomena(such as rainfall and snowfall)and human activities(such as underground pipeline leakage)may cause changes in the moisture content of unsaturated loess.The special engineering nature of loess collapsing with water seriously affects the safety and stability of buildings and structures in the loess area.The world spends huge amounts on repairing and transforming infrastructure in collapsible loess areas every year.As a traditional deep foundation form,pile foundation is widely used in loess areas.However,the design of pile foundation for collapsible loess area is still mainly based on saturated soil mechanics theory at this stage,and the influence of suction change and loess collapsibility on the bearing characteristics of pile foundation cannot be fully considered.As water seeps into the soil around the pile,the water content of the soil increases,the suction decreases,and the soil around the pile collapses and deforms.The reduction in suction leads to a decrease in the shear strength of the pile-soil interface,and the settlement of the soil around the pile leads to a relative displacement of the pile-soil.The two work together,resulting in a change in the bearing characteristics of the pile in unsaturated loess.Aiming at the above problems,this paper uses the method of indoor model test and theoretical analysis to carry out the following research:(1)This paper discusses the collapsibility mechanism of loess from the microscopic point of view,uses the improved regression analysis method to quantitatively analyze the correlation between the collapsibility coefficient of loess and its physical property index,obtains the prediction model for calculating the collapsibility coefficient,provides a simple method for predicting the collapsibility coefficient of a certain area.(2)Through indoor geotechnical tests,obtain the particle gradation curve,liquid plastic limit,optimal moisture content,maximum dry density,specific gravity,and collapsibility coefficient of the loess sample;through the SD-SWCC pressure plate tester,we get a soil-water characteristic curve was produced,and the F-X model was used to better fit the soil-water characteristic curve;the pile-soil interface shear test under different moisture contents was carried out,combined with the model proposed by Hamid and Miller,and the pile-soil was obtained.The relevant parameters in the interface shear strength;based on the similarity principle,the infiltration test of a single pile in unsaturated loess is carried out,and the law of the water content and suction of the soil around the pile over time during the humidification process is determined,and the settlement characteristics of the pile body change with time.The law of suction changes and the influence of humidification on the bearing characteristics of a single pile in unsaturated loess(including the axial force of the pile,the side friction of the pile,the resistance of the pile end and the settlement of the pile top)are analyzed.(3)Based on the principle of unsaturated soil mechanics,the traditional load transfer method is improved,mainly considering the influence of the change of matrix suction on the relative displacement of pile-soil and the shear strength of pile-soil interface.Through the development of a reliable program,the input includes the matrix suction curve during infiltration,the pile-soil interface and some basic parameters of the model pile to predict the changes in the bearing behavior of the pile in the unsaturated loess after infiltration.The theoretical calculation results and the indoor model test results are compared and analyzed to verify the feasibility of improving the load transfer curve method.