A Theoretical Analysis And Experimental Study On Compaction Pile Composite Foundation In Serious Collapsible Loess

With the development of economy, more and more foundation treatment problems of collapse loess with large thickness in construction field should be solved on loess of northwest China. To eliminate the collapsibility, decrease the Compression Deformation and enhance the bearing strength of collapse loess has become a difficult technical problem that need to be solved by engineers. In this thesis, by associated with the practical situation of applications in compaction pile composite foundation in loess, the theories and applications of loess compaction pile, lime-loess compaction pile and quicklime compaction pile composite foundation were lucubrated, and some suggestions were given to serve reference for further projects. The main content of this thesis includes:Firstly, based on the cavity expansion method, the stress variety discipline of soil between compaction piles during three different types piling process were studied according to elasto-plasticity theory. Moreover, when the soil was considered as the ideal Mohr-Coulomb material, its unified solutions were obtained.Secondly, based on the characteristics of compaction pile composite foundation, the variety discipline of physical and mechanical parameters of soil between piles were researched under the condition of horizontal pack-press, and its calculating formula of physical and mechanical parameters and compression modulus are presented. On the other hand, based on the principle of pore extruding, the computational formula for calculating the amount of expanding material of quicklime pile was deduced.Thirdly, by studying the calculate method of compaction pile composite foundation, the effect of influence factors of its bearing capacity was analyzed. Furthermore, the theoretical value of quicklime pile's swell, the total pile side resistance increment which caused by quicklime lateral swelling, the influence of normal stress and vertical bearing capacity of quicklime expansion ratio at interface of pile-soil, and the quantitative management formula of soil between quicklime piles were deduced.Lastly, by utilizing laboratory and in-situ test of practical project and numerical simulation (FLAC 3D), the compaction effects of soil between piles and bearing capacity of composite foundation are synthetic evaluated. The test results of quicklime compaction pile show that the bearing capacity is great larger than guild regulations suggested value. So, it is suggest that the design ultimate bearing capacity can be improved in engineering practice. By the test result of dig well, it shows that the quicklime hasn't cured completely in 28 days, it is because that the water content is low in loess. So we proposed that the time limit of repose need to be extend for more than 28 days.In summary, the work of this thesis present a comprehensive study of the compaction pile composite foundation strengthening mechanism, and provide a new theoretical and technical support to compaction pile composite foundation in thick loess ground treatment design and calculation. This will enrich and improve the compaction pile composite foundation theory and technology.