International Journal of Mining Science and Technology最新文献

The far-field microdynamic disturbance caused by the excavation of deep mineral resources and underground engineering can induce surrounding rock damage in high-stress conditions and even lead to disasters. However, the mechanical properties and damage/fracture evolution mechanisms of deep rock induced by microdynamic disturbance under three-dimensional stress states are unclear. Therefore, a true triaxial multilevel disturbance test method is proposed, which can completely simulate natural geostress, excavation stress redistribution (such as stress unloading, concentration and rotation), and subsequently the microdynamic disturbance triggering damaged rock failure. Based on a dynamic true triaxial test platform, true triaxial microdynamic disturbance tests under different frequency and amplitudes were carried out on monzogabbro. The results show that increasing amplitude or decreasing frequency diminishes the failure strength of monzogabbro. Deformation modulus gradually decreases during disturbance failure. As frequency and amplitude increase, the degradation rate of deformation modulus decreases slightly, disturbance dissipated energy increases significantly, and disturbance deformation anisotropy strengthens obviously. A damage model has been proposed to quantitatively characterize the disturbance-induced damage evolution at different frequency and amplitude under true triaxial stress. Before disturbance failure, the micro-tensile crack mechanism is dominant, and the micro-shear crack mechanism increases significantly at failure. With the increase of amplitude and frequency, the micro-shear crack mechanism increases. When approaching disturbance failure, the acoustic emission fractal dimension changes from a stable value to local large oscillation, and finally increases sharply to a high value at failure. Finally, the disturbance-induced failure mechanism of surrounding rock in deep engineering is clearly elucidated.

Water effects on the mechanical properties of rocks have been extensively investigated through experiments and numerical models. However, few studies have established a comprehensive link between the microscopic mechanisms of water-related micro-crack and the constitutive behaviors of rocks. In this work, we shall propose an extended micromechanical-based plastic damage model for understanding weakening effect induced by the presence of water between micro-crack’s surfaces on quasi-brittle rocks, based on the Mori-Tanaka homogenization and irreversible thermodynamics framework. Regarding the physical mechanism, water strengthens micro-crack propagation, which induces damage evolution during the pre- and post-stage, and weakens the elastic effective properties of rock matrix. After proposing a special calibration procedure for the determination of model parameters based on the laboratory compression tests, the proposed micromechanical-based model is verified by comparing the model predictions to the experimental results. The model effectively captures the mechanical behaviors of quasi-brittle rocks subjected to the weakening effects of water.

Chemical solvents instead of pure water being as hydraulic fracturing fluid could effectively increase permeability and improve clean methane extraction efficiency. However, pore-fracture variation features of lean coal synergistically affected by solvents have not been fully understood. Ultrasonic testing, nuclear magnetic resonance analysis, liquid phase mass spectrometry was adopted to comprehensively analyze pore-fracture change characteristics of lean coal treated by combined solvent (NMP and CS₂). Meanwhile, quantitative characterization of above changing properties was conducted using geometric fractal theory. Relationship model between permeability, fractal dimension and porosity were established. Results indicate that the end face fractures of coal are well developed after CS₂ and combined solvent treatments, of which, end face box-counting fractal dimensions range from 1.1227 to 1.4767. Maximum decreases in ultrasonic longitudinal wave velocity of coal affected by NMP, CS₂ and combined solvent are 2.700%, 20.521%, 22.454%, respectively. Solvent treatments could lead to increasing amount of both mesopores and macropores. Decrease ratio of fractal dimension D_s is 0.259%–2.159%, while permeability increases ratio of NMR ranges from 0.1904 to 6.4486. Meanwhile, combined solvent could dissolve coal polar and non-polar small molecules and expand flow space. Results could provide reference for solvent selection and parameter optimization of permeability-enhancement technology.

The damage evolution process of non-penetrating cracks often causes some unexpected engineering disasters. Gypsum specimens containing non-penetrating crack(s) are used to study the damage evolution and characteristics under cyclic loading. The results show that under cyclic loading, the relationship between the number of non-penetrating crack(s) and the characteristic parameters (cyclic number, peak stress, peak strain, failure stress, and failure strain) of the pre-cracked specimens can be represented by a decreasing linear function. The damage evolution equation is fitted by calibrating the accumulative plastic strain for each cycle, and the damage constitutive equation is proposed by the concept of effective stress. Additionally, non-penetrating cracks are more likely to cause uneven stress distribution, damage accumulation, and local failure of specimen. The local failure can change the stress distribution and relieve the inhibition of non-penetrating crack extension and eventually cause a dramatic destruction of the specimen. Therefore, the evolution process caused by non-penetrating cracks can be regarded as one of the important reasons for inducing rockburst. These results are expected to improve the understanding of the process of spalling formation and rockburst and can be used to analyze the stability of rocks or rock structures.

Rock fracture mechanisms can be inferred from moment tensors (MT) inverted from microseismic events. However, MT can only be inverted for events whose waveforms are acquired across a network of sensors. This is limiting for underground mines where the microseismic stations often lack azimuthal coverage. Thus, there is a need for a method to invert fracture mechanisms using waveforms acquired by a sparse microseismic network. Here, we present a novel, multi-scale framework to classify whether a rock crack contracts or dilates based on a single waveform. The framework consists of a deep learning model that is initially trained on 2400000+ manually labelled field-scale seismic and microseismic waveforms acquired across 692 stations. Transfer learning is then applied to fine-tune the model on 300000+ MT-labelled lab-scale acoustic emission waveforms from 39 individual experiments instrumented with different sensor layouts, loading, and rock types in training. The optimal model achieves over 86% F-score on unseen waveforms at both the lab- and field-scale. This model outperforms existing empirical methods in classification of rock fracture mechanisms monitored by a sparse microseismic network. This facilitates rapid assessment of, and early warning against, various rock engineering hazard such as induced earthquakes and rock bursts.

In deep hard rock excavation, stress plays a pivotal role in inducing stress-controlled failure. While the impact of excavation-induced stress disturbance on rock failure and tunnel stability has undergone comprehensive examination through laboratory tests and numerical simulations, its validation through in-situ stress tests remains unexplored. This study analyzes the three-dimensional stress changes in the surrounding rock at various depths, monitored during the excavation of B2 Lab in China Jinping Underground Laboratory Phase II (CJPL-II). The investigation delves into the three-dimensional stress variation characteristics in deep hard rock, encompassing stress components and principal stress. The results indicate changes in both the magnitude and direction of the principal stress during tunnel excavation. To quantitatively describe the degree of stress disturbance, a series of stress evaluation indexes are established based on the distances between stress tensors, including the stress disturbance index (SDI), the principal stress magnitude disturbance index (SDIm), and the principal stress direction disturbance index (SDId). The SDI indicates the greatest stress disturbance in the surrounding rock is 4.5 m from the tunnel wall in B2 Lab. SDIm shows that the principal stress magnitude disturbance peaks at 2.5 m from the tunnel wall. SDId reveals that the largest change in principal stress direction does not necessarily occur near the tunnel wall but at a specific depth from it. The established relationship between SDI and the depth of the excavation damaged zone (EDZ) can serve as a criterion for determining the depth of the EDZ in deep hard rock engineering. Additionally, it provides a reference for future construction and support considerations.

The quality upgrading and deashing of inferior coal by chemical method still faces great challenges. The dangers of strong acid, strong alkali, waste water and exhaust gas as well as high cost limit its industrial production. This paper systematically investigates the ash reduction and desilicification of two typical inferior coal utilizing ammonium fluoride roasting method. Under the optimal conditions, for fat coal and gas coal, the deashing rates are 69.02% and 54.13%, and the desilicification rates are 92.64% and 90.27%, respectively. The molar dosage of ammonium fluoride remains consistent for both coals; however, the gas coal, characterized by a lower ash and silica content (less than half that of the fat coal), achieves optimum deashing effect at a reduced time and temperature. The majority of silicon in coal transforms into gaseous ammonium fluorosilicate, subsequently preparing nanoscale amorphous silica with a purity of 99.90% through ammonia precipitation. Most of the fluorine in deashed coal are assigned in inorganic minerals, suggesting the possibility of further fluorine and ash removal via flotation. This research provides a green and facile route to deash inferior coal and produce nano-scale white carbon black simultaneously.

Deep-sea pipelines play a pivotal role in seabed mineral resource development, global energy and resource supply provision, network communication, and environmental protection. However, the placement of these pipelines on the seabed surface exposes them to potential risks arising from the complex deep-sea hydrodynamic and geological environment, particularly submarine slides. Historical incidents have highlighted the substantial damage to pipelines due to slides. Specifically, deep-sea fluidized slides (in a debris/mud flow or turbidity current physical state), characterized by high speed, pose a significant threat. Accurately assessing the impact forces exerted on pipelines by fluidized submarine slides is crucial for ensuring pipeline safety. This study aimed to provide a comprehensive overview of recent advancements in understanding pipeline impact forces caused by fluidized deep-sea slides, thereby identifying key factors and corresponding mechanisms that influence pipeline impact forces. These factors include the velocity, density, and shear behavior of deep-sea fluidized slides, as well as the geometry, stiffness, self-weight, and mechanical model of pipelines. Additionally, the interface contact conditions and spatial relations were examined within the context of deep-sea slides and their interactions with pipelines. Building upon a thorough review of these achievements, future directions were proposed for assessing and characterizing the key factors affecting slide impact loading on pipelines. A comprehensive understanding of these results is essential for the sustainable development of deep-sea pipeline projects associated with seabed resource development and the implementation of disaster prevention measures.

High-energy gas fracturing of shale is a novel, high efficacy and eco-friendly mining technique, which is a typical dynamic perturbing behavior. To effectively extract shale gas, it is important to understand the dynamic mechanical properties of shale. Dynamic experiments on shale subjected to true triaxial compression at different strain rates are first conducted in this research. The dynamic stress-strain curves, peak strain, peak stress and failure modes of shale are investigated. The results of the study indicate that the intermediate principal stress and the minor principal stress have the significant influence on the dynamic mechanical behaviors, although this effect decreases as the strain rate increases. The characteristics of compression-shear failure primarily occur in shale subjected to triaxial compression at high strain rates, which distinguishes it from the fragmentation characteristics observed in shale under dynamic uniaxial compression. Additionally, a numerical three-dimensional Split Hopkinson Pressure Bar (3D-SHPB), which is established by coupling PFC3D and FLAC3D methods, is validated to replicate the laboratory characteristics of shale. The dynamic mechanical characteristics of shale subjected to different confining stresses are systematically investigated by the coupling PFC3D and FLAC3D method. The numerical results are in good agreement with the experimental data.