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Dry Jet Mixing (DJM) is a commonly used in-situ soil improvement approach for increasing the strength and reduction on compressibility of soft marine clayey soils. However, the possibility of DJM improved soil achieving designed strength is largely dependent on the mixing process in that strength distribution of DJM improved soils is often scattered. This discreteness has been attributed to less homogeneity characteristic of mixed soil mass during the procedure of DJM. Given the discrete strength distribution of mixed soils, the strength of DJM improved soil applied in design is usually much lower than that obtained from the laboratory tests so that the security of geotechnical engineering projects can be guaranteed. Recently, with modifications of traditional DJM drill machine, it has become more likely that higher mixing homogeneity be achieved. “Double-Pole and Bidirectional Mixing” technology is just one of these modifications through which the strength of improved cement soil column can be increased. In this study, strength characteristics of column body were investigated both in laboratory using unconfined compressive strength test and in the field using standard penetration test. The test results reveal that bidirectional DJM method tends to attain a higher homogeneity thus increase bearing capacity of soft sediment. On the other hand, the strength of the bottom of column and the quality of column shaft can be improved as well. Due to potential advantages of bidirectional DJM technology above, the prospect of its application is promising.

It was an important problem to assessment Capacity of single pile. Several methods to determine axial pile capacity directly based on cone penetration test (CPT) data are presented and evaluated. Based on the SCPTU test results, the authors try to use penetration data to predict the pile side friction and the bearing capacity. The CPT methods, as well as the SCPTU methods, were used to estimate the load carrying capacities of the investigated piles (Qp). The pile load test was used to determine the measured load carrying capacities (Qm). The pile capacities determined using the different methods were compared with the measured pile capacities obtained from the pile load tests. Two criteria were selected as bases of evaluation: the best fit line for Qp versus Qm and the cumulative probability for the ratio Qp /Qm. Results of the analyses showed that the best methods for determining pile capacity are the two CPTU methods. Furthermore, the SCPTU method is simple, easy to apply, and independent of all operator subjective influence. It is especially suitable for use in pile engineering practice.

Clay microscopic structure, particle surface electric field and the interaction between ions in clay pore fluid have an important influence upon ion transport, but how to consider the influence of above factors on ion transport has been a difficult problem not solved. Establish microscopic Poisson-Nernst-Planck (hereinafter referred to as PNP) multi-ion transport model in the clay based on electrochemical theory, and obtain macroscopic PNP multi-ion transport model using volume Averaging. Combining the steady diffusion test of NaCl saline solution in the clay, this paper constructs clay microscopic particle model adopting randomly growing quartet structure generation set, introduces in detail the principles and steps of the upscaling from microscopic model to macroscopic model, and successfully upgrades microscopic model (nanometer level) to macroscopic model (centimeter and meter level) by numerical analysis. The macroscopic transport parameters are obtained from microscopic model upscaling and the boundary conditions are determined according to the solution results of macroscopic model, that is, microscopic-macroscopic conjoint analysis method is adopted to solve the problem of stepping over between different scales. And issues such as anion exclusion and cation adsorption difficult to be explained by the classical diffusion law have been discussed.

Poisson-Nernst-Planck (hereinafter referred to as PNP) is applied to describe ion transport in clay microscale structure and obtain the macroscopic PNP multi-ions transport model in clay through volume averaging. Use numerical analysis to research microscale quantities such as ion background concentration and particle surface charge density as well as the influence of clay microscale structure on macroscopic transport parameters (effective diffusion coefficients, effective charge density, effective porosity, etc). The research of parameters demonstrates that macroscopic transport parameters depend on ionic types, microscale structure, ion background concentration and particle surface charge density. The microscopic and macroscopic PNP multi-ions transport model can take into account the influences of clay microscale structure, electrochemical properties of solid-liquid interface, ion interaction and the interaction of ions and electric field in clay. The research result helps to deeply understand the diffusion transport mechanism of ions in the clay.

This paper constructs a parameter inverse analysis model for the diffusion analysis experiments of multi-ion transport model. It transforms multi-parameter inverse analysis problem into an optimization problem for nonlinear constrained planning. The optimization principle, the sequential quadratic programming method (SQP) for optimization and its implementation method in Matlab are introduced. With Comsol Multiphysics, multi-ion transport model is analyzed positively and is edited into the objective function (File .M) that can be directly utilized by Matlab. Then the fmincon function of the nonlinear optimization of Matlab to solve and analyze the problems. The proliferation tests of NaCl salt solution in the clay are under inverse analysis to obtain macro-transport parameters. The analysis shows that this method has fast convergence and high accuracy. This method is also beneficial to the similar optimization analysis of multi-parameter inverse analysis problems and complex nonlinear multi-field coupling problems.

According to the results of the pumping test, the problems of back analysis of Hydrogeologic parameters are changed into the optimization problem of a nonlinear constrained programming. By secondary development tools of Comsol, the M-file script for numerical solution of seepage problems of file has been compiled to achieve the seamless converting of the finite element analysis and Matlab optimization solution and to solve the difficult problem for solution and the problem that the face analysis and back analysis of traditional permeability coefficients are independent. The calculation analysis of samples shows that the algorithm converges very fast and very precise.