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In order to understand the influence of sand content on the secondary consolidation behavior of sand–fine mixtures, a series of one-dimensional creep tests were conducted. These tests used mixtures with sand contents of 0%, 16.67%, 28.57%, 50%, and 60% and were run for 3,000 min. As the sand content increases, the structure of the mixtures transitions from being fine-supported to sand-supported. This results in changes in the time at the end of primary consolidation (TEOP), the proportion of secondary consolidation deformation in the total deformation (PCT), and the coefficient of secondary consolidation. These parameters decrease before the sand content reaches 28.57% and increases after this point. The sand–fine mixtures with a sand content of 28.57% exhibit the minimum TEOP, PCT, and coefficient of secondary consolidation. When the sand content is less than 28.57%, bound water (especially weakly bound water) significantly impacts the secondary consolidation behavior of the sand–fine mixtures. However, when the sand content exceeds 28.57%, the secondary consolidation deformation of the mixtures is primarily governed by particle crushing in the sand grains. [ABSTRACT FROM AUTHOR]

An accurate description of the stress-strain relationships of sand-fine mixtures is very important to analyze the soil's mechanical properties. Hence, a series of consolidated drained (CD) triaxial tests were performed on reconstructed sand-silt mixtures with sand contents of 0%, 16.67%, 28.57%, 50%, and 60% in the paper to examine the effect of the sand content on the stress-strain curves of the soil. Results show that for sand-fine mixtures with different sand contents, the stress-strain curves are also mainly strain softening though there exist different degrees of softening. In order to quantitatively describe the strain-softening characteristics of sand-fine mixtures, a modified Duncan-Chang model was developed. To verify the applicability of the modified mode, examples such as coral clay and undisturbed loess are described and predicted. There is a high consistency between theoretical and experimental values. Finally, a sand-content-dependent constitutive model that considered the effects of sand content and confining pressure was proposed based on the modified Duncan-Chang model by constructing the relationship between model parameters and confining pressure and sand content. The constitutive model was implemented in ABAQUS software and verified by comparing the calculated results with the triaxial test data of sand-fine mixtures under the confining pressure of 500 kPa. The comparison results indicate that the constitutive model can reflect the real characteristics of sand-fine mixtures. [ABSTRACT FROM AUTHOR]

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 compare further and quantify the 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Islanding detection and prevention is a mandatory requirement for grid-connected distributed-generation systems. In this paper, we propose an antiislanding technique based on the proportional power spectral density of the voltage period at the point of common coupling (PCC). The concept of proportional power spectral density (PPSD) is introduced as a normalized measure that can be used for islanding detection. We show that if the voltage period measured at the PCC is filtered and used to set the command period of the inverter, then an islanding condition results in a distinct PPSD. The technique is implemented and demonstrated using a 4-kW inverter and verified in simulation. Index Terms--Antiislanding, distributed generation (DG), grid-interconnection, islanding detection, power spectral density.