Study On Squeezing Effect Of Jacked Pile Considering Structural Damage In Soft Soil

The precast concrete pile installed by jacking method is now widely used in civil engineering, especially in projects on soft clay. It has the advantages of excellent quality, high construction efficiency, lower cost, and no noise, vibration and slurry pollution, etc. But it was one type of displacement piles, it has an inherent disadvantage, the squeezing effect will do harm to the surrounding environment.Based on previous achievements of other scholars, the lateral stress and initial pore pressure were assumed to vary with depth, and the influence of soil structural strength was taken into account when analyzing the stress, displacement and excess pore water pressure by pile driving in the thesis. The main contents of this thesis are as follows:Firstly, the mechanical characteristics of natural clay were analyzed by the compressibility curve, variation of consolidation coefficient, distribution of excess pore water pressure and stress-strain relationship. Then the influence laws of structural strength on pile driving process were obtained.Secondly, based on a trilinear elasto-plastic model with strain softening, the structural damage characteristic of clay was considered. By using the spatial mobilization plane (SMP) theory and the governing equations of three-dimensional axisymmetric problem, the analytical solutions of the stress, strain, maximum radius of plastic zone, ultimate cavity pressure and displacement fields of the cylindrical cavity expansion were deduced. The results indicated that shear dilatancy, strain softening, structural damage and depth as well as the intermediate principal stress have considerable influence on both ultimate cavity pressure and maximum radius of plastic zone in the cylindrical cavity expansion.Thirdly, by using the non-associated flow rule and introducing the logarithmic strain, the elasto-plastic analytical solution of the cavity expansion was obtained considering large deformation of soils. The influences of large or small strain theory and considering the elastic deformation of the plastic zone or not on the solutions were discussed.Finally, the equation of initial pore pressures is deduced by using Henkel formula. By applying it in a practical example, it showed that the theoretical results were in accordance with measured data within the most scope of pile length.