Study On Soil Collapsibility Characteristics Of Piles In Composite Foundation Of Plain Concrete Piles In Loess

The composite foundation of plain concrete pile is widely used in the self-weight collapsible loess site.After the water immersion,the soil between the piles will have a downward displacement,and the pile will have an upward friction force on the soil between the piles,resulting in the unloading occurs during the soil being collapsible.and the soil has the special nature of unloading and collapsing.At present,there is a lack of research on the characteristics of soil collapsibility between piles in composite foundations with self-weight collapsible loess sites.This paper is based on experiments to carry out research work on this issue.This paper first considers the characteristics of continuous unloading when the soil between piles collapse process,defines the unloading and collapsibility parameters of loess,and carries out the conventional collapsibility test,single unloading and collapsing test,and then simulates the process of continuous unloading and collapsing.The unloading and collapsing test was carried out several times,and the law of unloading and collapsible deformation of loess was studied.The results show that under the same test conditions,the unloading and collapsibility coefficient of loess decreases with the decrease of unloading stress ratio.As the shrinkage completion ratio increases,it increases with the increase of the initial pressure;the unloading collapse deformation is mainly affected by the total unloading amount,the total collapsibility completion ratio and the initial pressure.Finally,based on the results of multiple unloading and collapsing tests,the unloading and collapsible deformation law of loess is summarized,and the evaluation method of loess collapsibility is improved.Based on the study of loess unloading and collapsibility test,based on the modulus reduction method,the soil collapsibility model between piles in the composite foundation of self-weight collapsible loess site was established,and the soil between piles was analyzed according to different working conditions.The characteristics of collapsible deformation show that the soil between the piles is affected by the negative frictional resistance,the additional stress is gradually reduced,and the unloading occurs along the soil during the collapsing process.The size of the collapsible deformation between the piles It is closely related to initial pressure,pile spacing,pile diameter and degree of collapsibility.With the increase of initial pressure,pile spacing and collapsibility,the collapsible deformation increases gradually.With the increase of pile diameter,the collapsible deformation decreases.The soil stress between piles increases with the increase of initial pressure and pile spacing,and decreases with the increase of pile diameter and collapsibility.Finally,combined with the numerical analysis results and the evaluation method of loess collapsibility,the calculation method of soil collapsible deformation between piles is proposed,It is of great significance to improve the design theory of composite concrete foundation of self-weight collapsible loess site,to promote and standardize its engineering application.