Research on crack evolution law and macroscopic failure mode of joint Phyllite under uniaxial compression

Numerical simulation of the effect of internal hole defect size on the mechanical properties of limestone

To better understand the effect of the size of hole defects on the mechanical properties of a rock mass, the two-dimensional particle flow discrete element code (PFC2D) is applied to establish rock mass models with single circular hole defects of different diameters. Uniaxial compressive strength (UCS) tests are conducted on each model by only taking the defect size (area) as a variable. This study analyzes each model's stress-strain, contact force chain, crack evolution, meso-damage and failure, and mechanical properties. The results showed that with the size enlargement of the circular hole defects, each model's UCS and elastic modulus gradually decrease, and the defect size is negatively correlated with the mechanical strength of the rock samples. The size of the hole defects affects the entire process of contact force chain and crack evolution. The larger the aperture dimension of the circular hole defects in each model, the greater the concentration degree of the contact force chain, the earlier the crack initiation, and the higher the degree of crack coalescence in the post-peak stage. The number of cracks decreases as the hole size increases, and the model is more prone to failure. Rock models' strength and failure characteristics with different numbers and arrangements of hole defects are discussed under the same defect area condition.

Experimental Study on the Influence of Confining Pressure and Bedding Angles on Mechanical Properties in Coal

Extensive bedding planes have a great influence on the mechanical properties of coal. In order to study the mechanism of the effects of bedding angles on the mechanical properties and failure characteristics of coal in the Shanxi Baode coal mine, uniaxial and triaxial compression tests and numerical simulations were conducted. The strength deterioration and microstructural changes in the samples were then analyzed with discrete element method (DEM) numerical simulation. The experimental results reveal that the power function strength criterion has good applicability to the strength characteristics of this coal. It was also found that the bedding angles have a great influence on the mechanical properties of coal. The properties of peak strength at different bedding angles roughly showed a U-shaped changing trend. The maximum strength occurred at a bedding angle of 0°, whereas the minimum strength occurred at a bedding angle of 60°. The numerical simulation and test results prove that the forms of failure of different bedding coal samples are complicated and are mainly represented by tensile and shear failures.

Meso fracture characteristics of granite and instability evolution law of surrounding rock in deep cavern

In order to analyze the influence of meso-structure and meso-parameters on deep granite characteristics, a construction method of variable radius proportional clump model was proposed with particle flow method. The clump particle flow structure was constructed which suited the mechanical characteristics of granite. The deep cavern numerical calculation model of gradual particle density was constructed using the variable radius proportional clump model construction method, and the macroscopic fracture law of deep cavern surrounding rock was analyzed. The results show that meso parameters have lower effects on the compressive and tensile ratios of particle structures in the ball and clump models. It is also found that clump structure is greatly influenced by particle proportion and size while ball model is only slightly influenced by particle size. Furthermore, the compressive and tensile strength curves and fracture modes of numerical simulations and laboratory tests are in good agreement. In addition, the calculated results of the tunnel after simulated excavation are very close to the engineering practice. There are obvious shear failure areas on the right vault and left wall of the tunnel, and the shape and depth of the fracture area are basically the same.