Min Zhang’s research while affiliated with Yellow River Institute of Hydraulic Research and other places

Accurate in apparatus, complex in operation, expensive in fund and plentiful in time, test of unsaturated soil is difficult. Influence of status of dry and wet and degree of compacting was not considered generally when Duncan-Chang model was be used to unsaturated soil. With parameters of model served as constants, it was not consistent with the practice that parameters would be changed with saturation and water content and its application would be limited. General triaxial tests of drainage and consolidation about dry density and water content combined are carried out, influence of relation between stress and strain about clay is discussed, mathematical equations of parameters of Duncan-Chang model are established, thus modified Duncan-Chang E-B model of unsaturated clay is carried out that influence of dry density and saturation can be considered. From study we can see, on the one hand, characteristics of stress and strain about unsaturated clay are influenced obviously by saturation and dry density, the main parameters of E-B model keep close correction with dry density and saturation, and the both mutual effect can be expressed by multiplication. On the other hand, status of compacting and process of gradual change from dry to wet can be described with modified E-B model. Thus it will be more complete in factors considered, inosculate in practice, and convenient for use.

Difficult in soil-water characteristic curve achieved, existence of non-uniqueness and indistinct in influence of unlinear deformation characteristics of soil about density and water content, deformation characteristics of unsaturated soil were studied difficultly with general triaxial test, thus direct application of unlinear Duncan-Chang model in unsaturated soil was restricted. General triaxial tests with combined dry density and water content are carried out, changing rules of parameters of Duncan-Chang model are summarized, mathematical functions between dry density, saturation and parameters of the model are established. Analysis shows that deformation characteristics of unsaturated clay are influenced obviously by saturation and dry density. Among them, the larger the saturation, the higher strain becomes under the condition of the same dry density and main stress difference, and the less the dry density, the higher strain becomes under the condition of the same saturation and main stress difference. Moreover, the main parameters of Duncan-Chang model keep close correction with dry density and saturation, and the both mutual effect can be expressed by multiplication. This shows that mechanical characteristics of unsaturated soil can be studied with general triaxial test, thus it will be used easily in project.

The soil unsaturated property is one of the main factors happening dike dangers such as craze and hole, even seriously slope collapse in the Yellow River dike. Based on the study of unsaturated mechanical experiment, the soil shear strength model formula can be proposed, and the changing rule of unsaturated soil mechanical properties be investigated for the typical levee soil of the Yellow River. It can provide theoretical and technical support for preventing the dike danger occurring, reducing the danger rate during the flood season, and establishing defend methods and instructing flood-defended.