Research On Bearing Behavior Of Composite Foundation In Collapsible Loess Area

China has a vast territory and complex and ever-changing geological conditions According to different engineering geology,bad foundation often needs to adopt different foundation treatment measures according to local conditions.Collapsible loess is an unsaturated and under consolidated soil,which is extremely harmful to the buildings.It can not only eliminate the collapsibility of loess but also greatly improve the bearing capacity of the foundation when combining the pure soil compaction pile and CFG pile.However,the theoretical research and engineering practice of bearing deformation of pure soil compaction pile&CFG pile composite foundation are not perfect,and it is necessary to conduct more in-depth researchThis article bases on the foundation treatment engineering project of a community in Qiaodong District,Zhangjiakou City.By consulting a large number of documents and the geotechnical investigation report of the project,by summarizing the design schemes and the relevant conditions on the construction site and the treatment measures,by conducting the indoor geotechnical tests,field in situ tests and numerical simulation analysis,the relationship between loess physical index and collapsibility is analyzed,the bearing deformation theory of the pure soil compaction pile&CFG pile composite foundation in collapsible loess area is deeply studied and analyzed,which will provide practical experience and theoretical support for similar foundation treatment projects.The specific research results of this article are as follows(1)The reinforcement mechanism and design requirements of pure soil compaction are analyzed and discussed,suggest that pure soil compaction can only eliminate the collapsibility of loess and cannot effectively improve bearing capacity of the foundation;the reinforcement mechanism and bearing deformation theory of CFG pile are summarized(2)The engineering project examples,optimization measures and design calculation process of pure soil compaction pile&CFG pile composite foundation are introduced in detail;Through the analysis of the geotechnical test data of the soil samples,the correlation between physical indexes such as the distribution depth,water content,dry density,porosity ratio,compression modulus and plasticity index of the loess and the collapsibility of the loess is obtained.(3)After taking soil samples by drilling to take indoor collapsibility test,it is found that pure soil compaction pile can effectively eliminate the collapsibility of loess;After taking light cone dynamic sounding test,it is found that the soil body is denser and the foundation bearing capacity is improved after being treated with pure soil compaction pile;After taking single pile vertical anti-pressure static load test,composite foundation vertical anti-pressure static load test and pile body integrity test,it is shown that the foundation treatment effect of pure soil compaction pile&CFG pile composite foundation in collapsible loess area is fine,the characteristic value of foundation bearing capacity meets the design requirements,and the CFG pile body is good.(4)After Combining with the actual engineering project,the MIDAS GTS NX software is used to carry out numerical simulation analysis of composite foundation bearing deformation characteristic,the bearing deformation laws of pure soil compaction pile&single CFG pile composite foundation and pure soil compaction pile&long and short CFG pile composite foundation are studied,and the force and displacement characteristics of CFG pile body are summarized.