Stress And Seepage Consolidation Analysis Based On Egg-shaped Model

Soft clay is widely spread in coastal regions. To satisfy the requirements of further development with economic growth, ground treatment of soft clay is necessary in large amount of projects. The classic theory is instructive for engineering practices, though it has lots of limitations. Especially for the treatment of super-soft soil with high water content, high compressibility, the traditional Terzaghi consolidation theory doesn’t have good performances in prediction. It has been an urgent question to make further research on the kind of engineering problems. On the other side, traditional soil constitutive models were proposed on the basis of solid mechanics. While soil is a kind of discontinuous media, the calculated results are far from reality. The property of structure is obvious in soft clay, while traditional constitutive models are incapable of taking it into considering. The property of soil structure is a comprehensive feature that considers spatial arrangement and mutual connect of opponents of soil. Shen Zhujiang pointed out in1996that the key problem for soil mechanics in21st century is to build mathematical model for soil structure, and the method is to combine macroscopic and microscopic. By working out the micro mechanism of plastic deformation, stress should be related to strain to rebuild constitutive model. After that, the seepage analysis for structural soil can enhance the understanding of structural soil in the process of consolidation.The development of large-strain consolidation theory is introduced firstly. It still stays in the one-dimension phrase for its complexity of controlling equation. On the basis of one-dimension large-strain consolidation theory proposed by Gibson, an large-strain analysis model involving radial seepage is put forward in the paper. Free-strain analysis can be made on vertical drain foundation.Comparisons are made between the assumptions of free strain and equal strain. The proposed model is applied in a project case to verify the guidance for engineering practices.For the research of structural soil constitutive model, a series of tests with different stress paths are made on man-made structural soil to determine the initial egg-shaped yield surface. A new elastic-plastic constitutive model is built for structural soil, with hardening parameter of plastic work, isotropic hardening law, and associated flow rule. By simulating triaxial tests, it shows the egg-shaped elastic-plastic model could perform the property of hardening well. For the ability of simulating strain softening, it deserves further research.The numerical development for egg-shaped elastic-plastic model is deeply discussed in the paper. Implicit stress integral algorithm (namely regression algorithm) in modified Newton-Raphson method is adopted to reflect the relationship of stress and strain. So The finite element program is stable and accurate. For seepage coupled problems, regression algorithm is also adopted. The main points in programming for coupled problems is discussed. Analysis on application examples are used to verify the program, which could reflect the properties for structural soil in the process of consolidation.