International Journal of Mining Science and Technology最新文献

Identifying the real fracture of rock hidden in acoustic emission (AE) source clusters (AE-depicted microcrack zone) remains challenging and crucial. Here we revealed the AE energy (representing dissipated energy) distribution rule in the rock microcrack zone and proposed an AE-energy-based method for identifying the real fracture. (1) A set of fracture experiments were performed on granite using wedge-loading, and the fracture process was detected and recorded by AE. The microcrack zone associated with the energy dissipation was characterized by AE sources and energy distribution, utilizing our self-developed AE analysis program (RockAE). (2) The accumulated AE energy, an index representing energy dissipation, across the AE-depicted microcrack zone followed the normal distribution model (the mean and variance relate to the real fracture path and the microcrack zone width). This result implies that the nucleation and coalescence of massive cracks (i.e., real fracture generation process) are supposed to follow a normal distribution. (3) Then, we obtained the real fracture extension path by joining the peak positions of the AE energy normal distribution curve at different cross-sections of the microcrack zone. Consequently, we distinguished between the microcrack zone and the concealed real fracture within it. The deviation was validated as slight as 1–3 mm.

Underground engineering often passes through water-rich fractured rock masses, which are prone to fracture and instability under the long-term coupling of in-situ stress field and pore water (P-W) pressure, ultimately threatening the stability of underground structures. In order to explore the mechanical properties of rocks under H-M coupling, the corresponding damage constitutive (D-C) model has become the focus of attention. Considering the inadequacy of the current research on rock strength parameters, energy evolution characteristics and D-C model under H-M coupling, the mechanical properties of typical sandstone samples are discussed based on laboratory tests. The results show that the variation of characteristic stresses of sandstone under H-M coupling conforms to the normalized attenuation equation and Mohr-Coulomb (M−C) criterion. The P-W pressure mechanism of sandstone exhibits a dynamic change from softening effect to H-M fracturing effect. The closure stress is mainly provided by cohesive strength, while the initiation stress, damage stress, and peak stress are jointly dominated by cohesive strength and friction strength. In addition, residual stress is attributed to the friction strength formed by the bite of the fracture surface. Subsequently, the energy evolution characteristics of sandstone under H-M coupling were studied, and it was found that P-W pressure weakened the energy storage capacity and energy dissipation capacity of sandstone, and H-M fracturing was an important factor in reducing its energy storage efficiency. Finally, combined with energy dissipation theory and statistical damage theory, two types of D-C models considering P-W pressure are proposed accordingly, and the model parameters can be determined by four methods. The application results indicate that the proposed and modified D-C models have high reliability, and can characterize the mechanical behavior of sandstone under H-M coupling, overcome the inconvenience of existing D-C models due to excessive mechanical parameters, and can be applied to the full-range stress–strain process. The results are conducive to revealing the deformation and damage mechanisms of rocks under H-M coupling, and can provide theoretical guidance for related engineering problems.

Water decoupling charge blasting excels in rock breaking, relying on its uniform pressure transmission and low energy dissipation. The water decoupling coefficients can adjust the contributions of the stress wave and quasi-static pressure. However, the quantitative relationship between the two contributions is unclear, and it is difficult to provide reasonable theoretical support for the design of water decoupling blasting. In this study, a theoretical model of blasting fracturing partitioning is established. The mechanical mechanism and determination method of the optimal decoupling coefficient are obtained. The reliability is verified through model experiments and a field test. The results show that with the increasing of decoupling coefficient, the rock breaking ability of blasting dynamic action decreases, while quasi-static action increases and then decreases. The ability of quasi-static action to wedge into cracks changes due to the spatial adjustment of the blast hole and crushed zone. The quasi-static action plays a leading role in the fracturing range, determining an optimal decoupling coefficient. The optimal water decoupling coefficient is not a fixed value, which can be obtained by the proposed theoretical model. Compared with the theoretical results, the maximum error in the model experiment results is 8.03%, and the error in the field test result is 3.04%.

To better understand the failure behaviours and strength of bolt-reinforced blocky rocks, large scale extensive laboratory experiments are carried out on blocky rock-like specimens with and without rockbolt reinforcement. The results show that both shear failure and tensile failure along joint surfaces are observed but the shear failure is a main controlling factor for the peak strength of the rock mass with and without rockbolts. The rockbolts are necked and shear deformation simultaneously happens in bolt‑reinforced rock specimens. As the joint dip angle increases, the joint shear failure becomes more dominant. The number of rockbolts has a significant impact on the peak strain and uniaxial compressive strength (UCS), but little influence on the deformation modulus of the rock mass. Using the Winkler beam model to represent the rockbolt behaviours, an analytical model for the prediction of the strength of bolt-reinforced blocky rocks is proposed. Good agreement between the UCS values predicted by proposed model and obtained from experiments suggest an encouraging performance of the proposed model. In addition, the performance of the proposed model is further assessed using published results in the literature, indicating the proposed model can be used effectively in the prediction of UCS of bolt-reinforced blocky rocks.

Fracture propagation in shale under in situ conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface (confining pressure σ_cp=0, room temperature (T_r)) and at depths of 1600 m (σ_cp=40 MPa, T_i=70 °C) and 3300 m (σ_cp=80 MPa, high temperature T_i=110 °C) in the study area. High in situ stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the in situ environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled in situ stress and temperature conditions rather than focusing on either in situ stress or temperature alone.

In order to alleviate the pressure on the supply of lithium resources, this research proposes the use of binary/ternary collectors with high selectivity and collecting ability to enhance the flotation purification of low-grade zinnwaldite ore. The binary collector is a mixture of dodecylamine polyoxyethylene ether and DL-2-octanol. A binary collector is added first, followed by sodium oleate, known as a ternary collector. Under acidic conditions, the recovery of Li₂O in the concentrate was increased by 8.26% with the binary collector and 13.70% with the ternary collector, compared to the dodecylamine polyoxyethylene ether. The binary collector enhanced the dispersibility of the single collector, while co-adsorption strengthened the hydrophobic nature of the zinnwaldite surface. Consequently, zinnwaldite particles, after the application of binary collector, displayed inter-particle flocculation and attachment to bubbles within 60×10⁻⁹ m compared to other particles. Ternary collector exhibited the capacity to lower critical micelle concentration and surface tension, subsequently inducing a denser and thicker hydrophobic layer through electrostatic forces, hydrophobic interactions, and chemical reactions. The objective of this research is to facilitate the recovery of lithium resources from low-grade ores in order to meet the needs of sustainable development.

Understanding the effects of microwave irradiation and thermal treatment on the dynamic compression and fragmentation properties of rocks is essential to quantify energy consumption in rock engineering. In this study, Fangshan granite (FG) specimens were exposed to microwave irradiation and heat treatment. The damage of FG specimens induced by these two methods was compared using X-ray CT scanning and ultrasonic wave method. The temperatures of FG after microwave irradiation and thermal treatment were effectively evaluated using a newly proposed technique. A novelty method for precisely determining the geometric features of fragments is developed to estimate the fragmentation energy. Thus, the dynamic uniaxial compressive strength (UCS), the dynamic fragmentation characteristics, and the fragmentation energy of FG after these two pretreatment methods can be reasonably compared. The noticeable distinction of loading rate effect on the dynamic UCS of FG between these two pretreatment methods is first observed. A relationship is established between the dynamic UCS and the damage induced by microwave irradiation and heat treatment. Moreover, fragmentation energy fan analysis is introduced to accurately compare the fragmentation properties of FG after two pretreatment methods in dynamic compression tests.