In the triaxial compression test of soil engineering, particle breakage may occur under the double action of axial and lateral loads. So, for the DDA simulation, the internal discretization of DDA block should be carried out at first. However, different discretization may affect the final simulation results. To solve this problem, the DDA numerical models based on triangular discretization, Voronoi discretization and no discretization are established to carry out the triaxial test simulation of coarse granular material, and the influence of different discretization of DDA block on mechanical properties of coarse granular materials was compared. An improved DDA was used to simulate the triaxial tests under different confining pressures, The numerical results show that the deviatoric stress-strain curves of the three discrete forms become steeper and the peak strength also increases with the increase of confining pressure. Under the same confining pressure, the deviatoric stress-strain curve with no discretization is the steepest and the peak strength is also the largest. Although deviatoric stress-strain curve of the triangular discretization is gentler, its peak strength is closer to that with no discretization compared with the Voronoi discretization. The triangular discretization model gradually changes from contraction to dilation in the loading process, and the higher the confining pressure is, the more obvious the contraction is. At the same time, the direction of contact force gradually changes from the initial minor principal stress direction to the major principal stress direction, forming an obvious force chain, and the final particle breakage mostly occurs in an 'X' shaped region. The developed DDA method can accurately reflect the evolution of mechanical properties of coarse granular materials under various working conditions, and the research results can provide reference for the discrete form of blocks in similar simulation.
The pivotal petrophysical attribute of coal seams, i.e., their wettability, profoundly influences coal mining productivity and gas prevention/exploitation strategies within mines, stemming from intricate coal-water and coal-gas interactions. To reveal the intricacies of the surface wettabilities of the macroscopic components of coal, an in-depth study, including microscopic characterization, proximate analysis, contact angle measurements, coal facies analysis, and permeability-stress correlation analysis under both dry and wet states, was conducted on high-rank coal samples from the Qinshui Coalfield in North China. The key findings revealed the occurrence of a sequential decrease in the contact angle and thus enhancement of the wettability from the vitrain to clarain to durain coal components based on tests conducted using distilled water on high-rank coal surfaces. This wettability enhancement was positively correlated with the coal ash yield and mineral matter abundance. The spatial and vertical variations in the coal wettability were primarily controlled by the historical evolution of the peat swamp environment. Notably, the contact angle measurements utilizing coal fine tablets exhibited greater sensitivity compared to polished sections, bolstering the scientific rigor and precision of the wettability assessments. Furthermore, as the effective stress intensifies, the permeability of the coal cores composed of macro-components (durain, vitrain, and clarain) decreased exponentially due to the spontaneous imbibition capability. This comprehensive study provides a reference for the optimal selection of water management strategies in coal mining operations, enhancing overall mining safety and profitability.
As a second-order Cartesian tensor, in-situ stress naturally inherits the abstraction and mystery of the mathematical concept of stress tensor. It is difficult to present the in-situ stress measurement data intuitively and judge the validity of the measurement data concisely. It is pointed out that the orthogonality between principal stress vectors is the only criterion to judge the correctness of in-situ stress measurement data. The error algorithm based on interval calculation theory and simple error estimation algorithm are established to measure the degree of deviation from orthogonality between principal stress vectors caused by truncation of in-situ stress azimuth data, which can be used as an effective criterion for the validity of measurement data. In order to visually express the in-situ stress measurement data and to clarify its relationship with the stability of surrounding rock of underground engineering, the all element presentation method integrating data validation, three-dimensional stress state and stress ellipses on characteristic sections is proposed, which can clearly distinguish whether the principal stress vector meets the orthogonality at a glance. At the same time, the anisotropy degree of initial stress state of surrounding rock and the stress evolution path caused by excavation and unloading can be obtained intuitively. Using the all element graphical expression method proposed in this paper can visualize and concretize the abstract concept, and has stronger indication, which is convenient for the application of practical engineering.
Abstract To reveal the deformation law and mechanism of bedding slopes under excavation unloading, an unloading rebound model of slope deformation is established on the basis of Mindlin’s strain solution, and a bedding-slip model of slope deformation is deduced on the basis of the Kalhaway constitutive model. Combining the two models, this study presents a computational model for the deformation response of bedding slope excavation. This model can reflect the mechanism of excavation unloading and the characteristics of rock mass structure. The reliability of the model is verified by comparing the calculated results of the analytical model with the experimental results in the laboratory. On this basis, the influences of excavation angle, excavation depth, and stratum thickness are analyzed by using several calculation examples. The calculation results show that the deformation induced by excavation increases with the increase in excavation angle or depth and decreases with the increase in stratum thickness. The excavation response of bedding slopes is mainly affected by the effect of unloading and the slip of the structural plane. Moreover, the unloading effect is controlled by the amount of excavation, and the rebound deformation of slopes is approximately linearly correlated with excavation volume. Bedding slip is affected by many factors because the increase in excavation angle or the amount of rock stratum leads to the increase in slip deformation. The proposed model can provide a basis for the deformation mechanism of bedding slopes under excavation.
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