查看更多>>摘要：Well-developed pores and cracks in coal reservoirs are the main venues for gas storage and migration. To investigate the multi-scale pore fractal characteristics, six coal samples of different rankings were studied using high-pressure mercury injection (HPMI), low-pressure nitrogen adsorption (LPGA-N2), and scan-ning electron microscopy (SEM) test methods. Based on the Frankel, Halsey and Hill (FHH) fractal theory, the Menger sponge model, Pores and Cracks Analysis System (PCAS), pore volume complexity (Dv), coal surface irregularity (Ds) and pore distribution heterogeneity (Dp) were studied and evaluated, respec-tively. The effect of three fractal dimensions on the gas adsorption ability was also analyzed with high-pressure isothermal gas adsorption experiments. Results show that pore structures within these coal samples have obvious fractal characteristics. A noticeable segmentation effect appears in the Dv1 and Dv2 fitting process, with the boundary size ranging from 36.00 to 182.95 nm, which helps differen-tiate diffusion pores and seepage fractures. The D values show an asymmetric U-shaped trend as the coal metamorphism increases, demonstrating that coalification greatly affects the pore fractal dimensions. The three fractal dimensions can characterize the difference in coal microstructure and reflect their influ-ence on gas adsorption ability. Langmuir volume (VL) has an evident and positive correlation with Ds val-ues, whereas Langmuir pressure (PL) is mainly affected by the combined action of Dv and Dp. This study will provide valuable knowledge for the appraisal of coal seam gas reservoirs of differently ranked coals.
查看更多>>摘要：To improve the accuracy of microseismic inversion, seismic anisotropy and moment tensor source should be carefully considered in the forward modelling stage. In this study, 3D microseismic anisotropy wave forward modelling with a moment tensor source was proposed. The modelling was carried out based on a rotated-staggered-grid (RSG) scheme. In contrast to staggered-grids, the RSG scheme defines the velocity components and densities at the same grid, as do the stress components and elastic parameters. Therefore, the elastic moduli do not need to be interpolated. In addition, the detailed formulation and implementation of moment-tensor source loaded on the RSG was presented by equating the source to the stress increments. Meanwhile, the RSG-based 3D wave equation forward modelling was performed in parallel using compute unified device architecture (CUDA) programming on a graphics processing unit (GPU) to improve its efficiency. Numerical simulations including homogeneous and anisotropic models were carried out using the method proposed in this paper, and compared with other methods to prove the reliability of this method. Furthermore, the high efficiency of the proposed approach was evaluated. The results show that the computational efficiency of proposed method can be improved by about two orders of magnitude compared with traditional central processing unit (CPU) computing methods. It could not only help the analysis of microseismic full wavefield records, but also provide support for pas-sive source inversion, including location and focal mechanism inversion, and velocities inversion.
查看更多>>摘要：Cracking behaviors of rocks significantly affect the safety and stability of the explorations of underground space and deep resources. To understand deeply the microscopic cracking process and mechanical prop-erty of rocks, X-ray micro-computed tomography (X-lCT) is applied to capture the rock microstructures. The digital color difference UNet (DCD-UNet)-based deep learning algorithm with 3D reconstruction is proposed to reconstruct the multiphase heterogeneity microstructure models of rocks. The microscopic cracking and mechanical properties are studied based on the proposed microstructure-based peridy-namic model. Results show that the DCD-UNet algorithm is more effective to recognize and to represent the microscopic multiphase heterogeneity of rocks. As damage characteristic index of multiphase rocks increases, transgranular cracks in the same grain phase, transgranular and intergranular cracks of pore-grain phase, intergranular and secondary transgranular cracks and transgranular crack between dif-ferent grains propagate. The ultimate microscopic failure modes of rocks are mainly controlled by the transgranular cracks-based T1-shear, T3-shear, T1-tension, T2-tension and T3-tension failures, and the intergranular cracks-based T1-tension, T1-shear and T3-shear failures under uniaxial compression.
查看更多>>摘要：When the traditional drill and blast method is applied to rock crushing projects, it has strong vibration, loud noise and dust pollution, so it cannot be used in densely populated areas such as urban public works. We developed a supercritical CO2 true triaxial pneumatic rock-breaking experimental system, and con-ducted laboratory and field tests of dry ice powder pneumatic rock-breaking. The characteristics of the blast-induced vibration velocity waveform and the evolution of the vibration velocity and frequency with the focal distance were analyzed and discussed. The fracturing mechanism of dry ice powder pneumatic rock breaking is studied. The research results show that: (1) The vibration velocity induced by dry ice powder pneumatic rock breaking decays as a power function with the increase of the focal distance;(2) The vibration frequency caused by dry ice powder pneumatic rock breaking is mainly distributed in 1–120 Hz. Due to the dispersion effect, the dominant frequency of 10–30 Hz appears abnormally atten-uated;(3) The traditional CO2 phase change fracturing energy calculation formula is also applicable to dry ice pneumatic rock breaking technology, and the trinitrotoluene (TNT) equivalent of fracturing energy is applicable to the Sadovsky formula;(4) Dry ice powder pneumatic rock breaking is shock wave and high-energy gas acting together to fracture rock, which can be divided into three stages, among which the gas wedge action of high-energy gas plays a dominant role in rock mass damage.
查看更多>>摘要：The damage-fracture evolution of deep rock mass has obvious particularity, which is revealed in 2400-m-deep tunnels by field tests. The evolution of the excavation damaged zone depth is consistent with that of the fractured zone depth. The ratio of the excavation damaged zone depth to the excavation fractured zone depth is greater than 2.0 in a rock mass with both high strength and good integrity, but less than 1.5 in a rock mass with lower strength or poor integrity. Zonal disintegration in a rock mass with high strength and fair integrity is more likely to occur when it contains more than two groups of primary frac-tures in damaged zones. Fractures develop outward in zonal disintegration but are totally different from the single-zone fracture, in which the fractures develop inward, and it is the starting position of the frac-tured zone when the excavation surface of the middle pilot is 7–9 m close to the pre-set borehole and it stops after the excavation surface of the baseplate is 11–14 m away. The most intense evolution occurs around 2–4 m from the pre-set borehole in the sidewall expansion stage. The research results provide a reference for the monitoring scheme and support design of CJPL-Ⅲ in its future construction.
查看更多>>摘要：A failure criterion fully considering the anisotropy and hydration of shale is essential for shale formation stability evaluation. Thus, a novel failure criterion for hydration shale is developed by using Jaeger's shear failure criterion to describe the anisotropy and using the shear strength reduction caused by clay miner-als hydration to evaluate the hydration. This failure criterion is defined with four parameters in Jaeger's shear failure criterion (S1, S2, a and u), three hydration parameters (k, xsh and rs) and two material size parameters (d and l0). The physical meanings and determining procedures of these parameters are described. The accuracy and applicability of this failure criterion are examined using the published exper-imental data, showing a cohesive agreement between the predicted values and the testing results, R2=0.916 and AAREP (average absolute relative error percentage) of 9.260％. The error (|Dp|) is then dis-cussed considering the effects of b (angle between bedding plane versus axial loading), moisture content and confining pressure, presenting that |Dp| increases when b is closer to 30?, and |Dp| decreases with decreasing moisture content and with increasing confining pressure. Moreover, |Dp|is demonstrated as being sensitive to S1 and being steady with decrease in the data set when b is 0?, 30?, 45? and 90?.
查看更多>>摘要：A fractal model governing saw-tooth fractures was first introduced to replicate sandstone samples con-taining an inclined 3D penetrating rough fracture surface with various joint roughness coefficients (JRC). In conventional triaxial compression, the peak strength for fractured samples increased with both confin-ing pressure and JRC. During the unloading confining pressure process, the normal stress of fractures declined but the shear stress increased, resulting in shear sliding of fractures. The shear displacement of fractures exponentially increased, and the positive normal displacement decreased gradually to nega-tive values under coupling effects of shear contraction caused by normal stress and shear dilation due to climbing effects of fractures. Transition from quasi-static to dynamic sliding of the fractures was identi-fied. The sliding resistance duration increased with confining pressure but decreased with JRC. After pre-peak unloading, the fracture surfaces presented a more significant surface wear response and JRC values decreased by 1.70％–59.20％due to more remarkable asperity degradation compared with those after con-ventional triaxial compression. The theoretical model for shear strength of fractures was established through improving the Ladanyi&Archambault model by introducing the relations between normal stress and surface wear ratios of fractures, which agreed well with the experimental results.
查看更多>>摘要：The quantitative determination and evaluation of rock brittleness are crucial for the estimation of exca-vation efficiency and the improvement of hydraulic fracturing efficiency. Therefore, a'three-stage"triax-ial loading and unloading stress path is designed and proposed. Subsequently, six brittleness indices are selected. In addition, the evolution characteristics of the six brittleness indices selected are characterized based on the bedding effect and the effect of confining pressure. Then, the entropy weight method (EWM) is introduced to assign weight to the six brittleness indices, and the comprehensive brittleness index Bc is defined and evaluated. Next, the new brittleness classification standard is determined, and the brittleness differences between the two stress paths are quantified. Finally, compared with the previous evaluation methods, the rationality of the proposed comprehensive brittleness index Bc is also verified. These results indicate that the proposed brittleness index Bc can reflect the brittle characteristics of deep bedded sand-stone from the perspective of the whole life-cycle evolution process. Accordingly, the method proposed seems to offer reliable evaluations of the brittleness of deep bedded sandstone in deep engineering prac-tices, although further validation is necessary.
查看更多>>摘要：Adhesion is an important process of particle-bubble interaction in fine particle (?10 lm) flotation. This paper studied the adhesion process and mechanism between nanobubbles and fine cassiterite particles by using a high-speed camera, atomic force microscope (AFM), adsorption capacity tests, and induction time tests. After being pretreated with nanobubbles (NBs) water, fine cassiterite particles flotation tests were carried out using caprylhydroxamic acid (CHA) as a collector. The results showed that NBs can improve the recovery and flotation rate of fine cassiterite while decreasing the collector dosage. The adsorption capacity test indicated that the cassiterite treated with NBs had lower demand for collector concentration. The AFM imaging results further demonstrate that NBs could reduce the adsorption of CHA on the surface of minerals. Since NBs played a part of the role of collector, it can improve the flota-tion effect while reducing the amount of collector. The induction time test and the high-speed camera observation test showed that NBs promoted the attachment between bubbles and cassiterite particles. On the other hand, NBs agglomerate cassiterite particles, increasing the probability of particles colliding with bubbles.
查看更多>>摘要：In this work, the effect of ammonium sulfate on the adsorption characteristics of low-concentration Pb(II) ions on the sulfidized hemimorphite surface was comprehensively investigated. The results showed that ammonium sulfate could increase the maximum recovery of hemimorphite from 69.42％to 88.24％under a low concentration of Pb(II) ions. On the hemimorphite surface pretreated with ammonium sulfate, the adsorption of Pb(II) ions was enhanced and the main species of Pb adsorbed was changed from Pb―O/OH to PbS. This was due to the larger amount of ZnS providing more effective adsorption sites for Pb compo-nents to generate PbS. Meanwhile, the intensity of ZnS decreased with the formation of PbS, demonstrat-ing that ZnS was covered by PbS which formed later on the mineral surface. It was beneficial for the adsorption of butyl xanthate on the hemimorphite surface to form more hydrophobic substances. As a result, ammonium sulfate played a crucial role in realizing the efficient recovery of hemimorphite.
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