In this paper, the correlation between the particle size and rheological properties of MRE was discussed through both experimental results and theoretical analysis. It shows that the particle size can significantly influence the magnetorheological effect by changing the initial shear modulus and the saturated magnetic-induced shear modulus . With an increase in the particle size, the initial shear modulus gets lower, and the saturated magnetic-induced shear modulus increases to the maximum and then decreases. The larger the particle size is, the longer the distance between neighbor particles along the magnetic field is. Based on the relationship between the particle size and shear modulus, there exists an optimum size for added particles. Moreover, the performance of MRE can be improved by optimizing the particle size based on those rules.
Studying the true triaxial deformation characteristics and progressive damage behavior of sandstone is of great significance for the stability control of roadways. Both the conventional triaxial test (CTT) and the true triaxial compression test (TTT) were conducted for sandstone to investigate its deformation characteristics and the variation laws of volume strain during the progressive damage process under different confining pressures. The conducted experiments showed that both the axial and lateral strains of the rock prior to failure under CTT conditions increased with increasing confining pressure. However, with increasing intermediate principal stress (
σ
2
) under TTT conditions, both the axial strain, and the lateral strain (
ε
2
) gradually decreased, and the lateral strain (
ε
3
, expansion) first slow down and then accelerated. Moreover, the anisotropic characteristics first gradually weakened and then enhanced. The variation of the volume strain increment and the volume strain rate of rock combined with the acoustic emission activity and a three-dimensional rock theoretical model with microcrack defects were analyzed in detail. During the stable crack growth stage III, the volume strain increment and volume strain rate increased with increasing confining pressure under CTT conditions, while they decrease after the initial increase with increasing
σ
2
under TTT conditions. During the unstable crack growth stage IV, the volume strain increment increased sharply, while the volume strain rate gradually slowed down with increasing confining pressure under CTT conditions. The internal cracks of the rock were gradually suppressed and the lateral expansion was gradually constrained. The volume strain increment first increased followed by a decrease, and the volume strain rate gradually slowed down after a noticeable acceleration with increasing
σ
2
under TTT conditions. The internal micro-cracks gradually evolved from inhibition (in the planes parallel to plane 1–2 and plane 2–3) to accelerated expansion (the planes along the
σ
2
direction), and the lateral deformation first weakened and then strengthened.
In coal mines, under high in situ stress and strong mining activity, roadway surrounding rock commonly contains large amounts of larger fractures and microfractures. Along with the large deformation and continuous rheology of the soft rock roadway, the fractures in the surrounding rock are likely to be compressed and closed, forming undeveloped microfractures, which hinder conventional grouting support methods. Based on the fluid-solid coupling between slurry seepage and microfracture deformation, a theoretical model of microfracture grouting seepage is established. A program for the analysis and calculation of microfracture grouting is developed to quantitatively describe the variation in slurry seepage distance and fracture opening. Numerical experiments are carried out to study the grouting seepage of microfractures under different grouting pressures and fracture opening conditions, and the variation rules for the spatial distribution of fracture opening and slurry seepage distance during grouting pressure are obtained. Fluid-solid coupling has a significant influence on grout seepage characteristics. The grouting pressure and the fracture opening changes are nonlinearly attenuated along the grout seepage direction.
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