International Journal of Mining Science and Technology最新文献

To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading, fatigue tests under different upper-limit stresses were carried out on salt rock, and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument. Based on the test results, the effects of the cycle number and the upper-limit stress on the evolution of cracks, pore morphology, pore number, pore volume, pore size, plane porosity, and volume porosity of salt rock were analyzed. The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity. The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number. In order to describe the fatigue deformation behavior of salt rock under cyclic loading, the nonlinear Burgers damage constitutive model was further established. The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.

With an extension of the geological entropy concept in porous media, the approach called directional entrogram is applied to link hydraulic behavior to the anisotropy of the 3D fracture networks. A metric called directional entropic scale is used to measure the anisotropy of spatial order in different directions. Compared with the traditional connectivity indexes based on the statistics of fracture geometry, the directional entropic scale is capable to quantify the anisotropy of connectivity and hydraulic conductivity in heterogeneous 3D fracture networks. According to the numerical analysis of directional entrogram and fluid flow in a number of the 3D fracture networks, the hydraulic conductivities and entropic scales in different directions both increase with spatial order (i.e., trace length decreasing and spacing increasing) and are independent of the dip angle. As a result, the nonlinear correlation between the hydraulic conductivities and entropic scales from different directions can be unified as quadratic polynomial function, which can shed light on the anisotropic effect of spatial order and global entropy on the heterogeneous hydraulic behaviors.

Effective monitoring of the structural health of combined coal-rock under complex geological conditions by pressure stimulated currents (PSCs) has great potential for the understanding of dynamic disasters in underground engineering. To reveal the effect of this way, the uniaxial compression experiments with PSC monitoring were conducted on three types of coal-rock combination samples with different strength combinations. The mechanism explanation of PSCs are investigated by resistivity test, atomic force microscopy (AFM) and computed tomography (CT) methods, and a PSC flow model based on progressive failure process is proposed. The influence of strength combinations on PSCs in the progressive failure process are emphasized. The results show the PSC responses between rock part, coal part and the two components are different, which are affected by multi-scale fracture characteristics and electrical properties. As the rock strength decreases, the progressive failure process changes obviously with the influence range of interface constraint effect decreasing, resulting in the different responses of PSC strength and direction in different parts to fracture behaviors. The PSC flow model is initially validated by the relationship between the accumulated charges of different parts. The results are expected to provide a new reference and method for mining design and roadway quality assessment.

The technology of drilling tests makes it possible to obtain the strength parameter of rock accurately in situ. In this paper, a new rock cutting analysis model that considers the influence of the rock crushing zone (RCZ) is built. The formula for an ultimate cutting force is established based on the limit equilibrium principle. The relationship between digital drilling parameters (DDP) and the c-φ parameter (DDP-cφ formula, where c refers to the cohesion and φ refers to the internal friction angle) is derived, and the response of drilling parameters and cutting ratio to the strength parameters is analyzed. The drilling-based measuring method for the c-φ parameter of rock is constructed. The laboratory verification test is then completed, and the difference in results between the drilling test and the compression test is less than 6%. On this basis, in-situ rock drilling tests in a traffic tunnel and a coal mine roadway are carried out, and the strength parameters of the surrounding rock are effectively tested. The average difference ratio of the results is less than 11%, which verifies the effectiveness of the proposed method for obtaining the strength parameters based on digital drilling. This study provides methodological support for field testing of rock strength parameters.

Understanding the variations in microscopic pore-fracture structures (MPFS) during coal creep under pore pressure and stress coupling is crucial for coal mining and effective gas treatment. In this manuscript, a triaxial creep test on deep coal at various pore pressures using a test system that combines in-situ mechanical loading with real-time nuclear magnetic resonance (NMR) detection was conducted. Full-scale quantitative characterization, online real-time detection, and visualization of MPFS during coal creep influenced by pore pressure and stress coupling were performed using NMR and NMR imaging (NMRI) techniques. The results revealed that seepage pores and microfractures (SPM) undergo the most significant changes during coal creep, with creep failure gradually expanding from dense primary pore fractures. Pore pressure presence promotes MPFS development primarily by inhibiting SPM compression and encouraging adsorption pores (AP) to evolve into SPM. Coal enters the accelerated creep stage earlier at lower stress levels, resulting in more pronounced creep deformation. The connection between the micro and macro values was established, demonstrating that increased porosity at different pore pressures leads to a negative exponential decay of the viscosity coefficient. The Newton dashpot in the ideal viscoplastic body and the Burgers model was improved using NMR experimental results, and a creep model that considers pore pressure and stress coupling using variable-order fractional operators was developed. The model’s reasonableness was confirmed using creep experimental data. The damage-state adjustment factors ω and β were identified through a parameter sensitivity analysis to characterize the effect of pore pressure and stress coupling on the creep damage characteristics (size and degree of difficulty) of coal.

Deep-sea sediment disturbance may occur when collecting polymetallic nodules, resulting in the creation of plumes that could have a negative impact on the ecological environment. This study aims to investigate the potential solution of using polyaluminum chloride (PAC) in the water jet. The effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining area. The experimental results showed that the optimal PAC dose was found to be 0.75 g/L. Compared with the test conditions without the addition of PAC, the presence of PAC leads to a reduction in volume, lower characteristic turbidity, smaller diffusion velocity, and shorter settling time of the plume. This indicates that PAC inhibits the entire development process of the plume. The addition of PAC leads to the flocculation of mm-sized particles, resulting in the formation of cm-sized flocs. The flocculation of particles decreases the rate of erosion on the seabed by around 30%. This reduction in erosion helps to decrease the formation of plumes. Additionally, when the size of suspended particles increases, it reduces the scale at which they diffuse. Furthermore, the settling velocity of flocs (around 10⁻² m/s) is much higher that of compared to sediment particles (around 10⁻⁵ m/s), which effectively reduces the amount of time the plume remains in suspension.

Hydraulic-electric rock fragmentation (HERF) plays a significant role in improving the efficiency of high voltage pulse rock breaking. However, the underlying mechanism of HERF remains unclear. In this study, considering the heterogeneity of the rock, microscopic thermodynamic properties, and shockwave time domain waveforms, based on the shockwave model, digital imaging technology and the discrete element method, the cyclic loading numerical simulations of HERF is achieved by coupling electrical, thermal, and solid mechanics under different formation temperatures, confining pressure, initial peak voltage, electrode bit diameter, and loading times. Meanwhile, the HERF discharge system is conducive to the laboratory experiments with various electrical parameters and the resulting broken pits are numerically reconstructed to obtain the geometric parameters. The results show that, the completely broken area consists of powdery rock debris. In the pre-broken zone, the mineral cementation of the rock determines the transition of type C_Ⅰ cracks to type C_Ⅱ and type C_Ⅲ cracks. Furthermore, the peak pressure of the shockwave increased with initial peak voltage but decreased with electrode bit diameter, while the wave front time reduced. Moreover, increasing well depth, formation temperature and confining pressure augment and inhibit HERF, but once confining pressure surpassed the threshold of 60 MPa for 152.40, 215.90, and 228.60 mm electrode bits, and 40 MPa for 309.88 mm electrode bits, HERF is promoted. Additionally, for the same kind of rock, the volume and width of the broken pit increase with higher initial peak voltage and rock fissures will promote HERF. Eventually, the electrode drill bit with a 215.90 mm diameter is more suitable for drilling pink granite. This research contributes to a better microscopic understanding of HERF and provides valuable insights for electrode bit selection, as well as the optimization of circuit parameters for HERF technology.

The scientific community recognizes the seriousness of rockbursts and the need for effective mitigation measures. The literature reports various successful applications of machine learning (ML) models for rockburst assessment; however, a significant question remains unanswered: How reliable are these models, and at what confidence level are classifications made? Typically, ML models output single rockburst grade even in the face of intricate and out-of-distribution samples, without any associated confidence value. Given the susceptibility of ML models to errors, it becomes imperative to quantify their uncertainty to prevent consequential failures. To address this issue, we propose a conformal prediction (CP) framework built on traditional ML models (extreme gradient boosting and random forest) to generate valid classifications of rockburst while producing a measure of confidence for its output. The proposed framework guarantees marginal coverage and, in most cases, conditional coverage on the test dataset. The CP was evaluated on a rockburst case in the Sanshandao Gold Mine in China, where it achieved high coverage and efficiency at applicable confidence levels. Significantly, the CP identified several “confident” classifications from the traditional ML model as unreliable, necessitating expert verification for informed decision-making. The proposed framework improves the reliability and accuracy of rockburst assessments, with the potential to bolster user confidence.