The impacts of fine content on the microstructure and mechanical behavior of five types of coarse-fine particle mixtures with different fine contents are examined based on laboratory tests. The samples used in these tests all had a void ratio of 0.6. As the fine content decreases, the pore-size distribution of the soil changes from unimodal to bimodal, and the variation rate of the initial elastic modulus with confining pressure becomes great. If the fine content is greater than 71.43%, the pore volume of the mixtures reduces progressively progressively with decreasing the fine content, resulting in the growth of peak deviator stress, cohesiveness, and internal friction angle. If the concentration of the fine grains is less than 71.43%, the pore volume of the mixtures shows an increasing trend, which causes a decrease in peak deviator stress,cohesiveness, and internal friction angle.

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Dual-porosity and bi-dispersed porous media (DBPM) widely exist in geotechnical engineering, material engineering, soil science, and groundwater exploitation. Therefore, it is significant to quantify the relationship between permeability and matrix-fracture structure parameters for mastering fluid's seepage and transport characteristics. Hence, this paper derives an analytical solution of equivalent permeability for DBPM based on the intermingled fractal units (IFU). The developed model considers the capillary pressure of fractures and capillaries and the tortuosity of fractures and capillaries. Specifically, the number of porous matrix fractal units in IFU is quantified, and then the dimensionless permeability is calculated, defined as the ratio of the permeability of n p matrix fractal units to a single fracture fractal unit. The results reveal that equivalent permeability is mainly contributed by fracture permeability. Next, the second dimensionless permeability is defined to further compare and quantify permeable ability of fracture and porous matrix. The results highlight that the permeability difference between a single fracture fractal unit and a single porous matrix fractal unit is approximately 7-11 orders of magnitude. Overall, through this paper, the preferential flow mechanism of DBPM can be better described and understood by introducing the above two dimensionless permeabilities and analyzing the influence of structural parameters on them.

According to experimental findings, soft clay has compression and shear creep. The goal of the study is to develop an elastic-viscoplastic (EVP) model for the viscous behavior of soft clay. The new EVP model is deduced from the associated flow rule, Yin’s double-yield surface theory, and the critical state soil mechanics. The nonstationary flow surface model with double-yield surface, compared to other existing models, considers the compression and shear creep properties of soft clay. The model parameters can be identified from two sorts of tests (i.e., the general triaxial tests and triaxial rheological tests). Different types of soft clay, such as Tianjin Coastal clay, Shantou dredger fill, and silted soil in front of dam, were tested to verify the accuracy of the constructed model. All comparisons of computed and experimental findings revealed that the new EVP model accurately reflected the time-dependent behaviors of soft clay in both shear and compression creep.