Study On Negative Skin Friction In Post-Processed High Fill Subgrade

Post-processing technology used in the construction progress of high fill subgrade which locates on the soft ground is a newly developed roadbed treatment methodology recently. It has been successfully introduced to many highway projects and has achieved good social and economic benefits.Rigid non-sand concrete micro-piles in the composite high fill subgrade would thrust into the upper layer under the flexible load of the roadbed fill. This would cause the difference of settlement between the piles and the surrounding soil, leading to negative skin friction acting on the micropiles. Negative skin friction can transfer the load in the fill to a greater depth in the roadbed. This optimizes the load transfer model and would be used in the optimization design methodology for the high fill subgrade. The developmental and distributional character of negative skin friction and load transfer mechanism in the composite high fill subgrade is the key concern in the post-processing technology.In this thesis, the development of negative skin friction and the influence on the deformation behavior of the composite foundation is researched using the methodology of numerical modeling and theoretical analysis:A numerical model which describes the post-processed high fill subgrade is used in the analysis. Based on the numerical model, in the construction and service period, the developmental tendency of the deformation, pore water pressure, and effective stress is analyzed. The characteristic of the distribution and development of the negative skin friction and the axial stress acting on micro-piles is also discussed. The load transfer mechanism in the post-processed composite high fill subgrade is proposed. Using the numerical methodology, important design parameters of the post-processing technology such as initial consolidation degree of the composite subgrade, stiffness of the bearing stratum and the weak layer, the height and stiffness of the subsequent fill layer after post-processing are discussed for their influence on the engineering behavior of the post-processed high fill subgrade.A calculation model of the pile axial stress based on the elastic theory is developed. Examples analyses using the parameters of the numerical model is introduced to examine the theory calculation model. The result of the theory model is compared with that of the numerical model. The result proves its validity.Base on the result of this research, suggestions of the further research regarding the post-processed composite foundation are advised.