Journal of Central South University最新文献

Bedding structural planes significantly influence the mechanical properties and stability of engineering rock masses. This study conducts uniaxial compression tests on layered sandstone with various bedding angles (0°, 15°, 30°, 45°, 60°, 75° and 90°) to explore the impact of bedding angle on the deformational mechanical response, failure mode, and damage evolution processes of rocks. It develops a damage model based on the Logistic equation derived from the modulus’s degradation considering the combined effect of the sandstone bedding dip angle and load. This model is employed to study the damage accumulation state and its evolution within the layered rock mass. This research also introduces a piecewise constitutive model that considers the initial compaction characteristics to simulate the whole deformation process of layered sandstone under uniaxial compression. The results revealed that as the bedding angle increases from 0° to 90°, the uniaxial compressive strength and elastic modulus of layered sandstone significantly decrease, slightly increase, and then decline again. The corresponding failure modes transition from splitting tensile failure to slipping shear failure and back to splitting tensile failure. As indicated by the modulus’s degradation, the damage characteristics can be categorized into four stages: initial no damage, damage initiation, damage acceleration, and damage deceleration termination. The theoretical damage model based on the Logistic equation effectively simulates and predicts the entire damage evolution process. Moreover, the theoretical constitutive model curves closely align with the actual stress – strain curves of layered sandstone under uniaxial compression. The introduced constitutive model is concise, with fewer parameters, a straightforward parameter determination process, and a clear physical interpretation. This study offers valuable insights into the theory of layered rock mechanics and holds implications for ensuring the safety of rock engineering.

This study is the result of long-term efforts of the authors’ team to assess ground response of gob-side entry by roof cutting (GSERC) with hard main roof, aiming at scientific control for GSERC deformation. A comprehensive field measurement program was conducted to determine entry deformation, roof fracture zone, and anchor bolt (cable) loading. The results indicate that GSERC deformation presents asymmetric characteristics. The maximum convergence near roof cutting side is 458 mm during the primary use process and 1120 mm during the secondary reuse process. The entry deformation is closely associated with the primary development stage, primary use stage, and secondary reuse stage. The key block movement of roof cutting structure, a complex stress environment, and a mismatch in the supporting design scheme are the failure mechanism of GSERC. A controlling ideology for mining states, including regional and stage divisions, was proposed. Both dynamic and permanent support schemes have been implemented in the field. Engineering practice results indicate that the new support scheme can efficiently ensure long-term entry safety and could be a reliable approach for other engineering practices.

Non-pillar mining technology with automatically formed roadway is a new mining method without coal pillar reservation and roadway excavation. The stability control of automatically formed roadway is the key to the successful application of the new method. In order to realize the stability control of the roadway surrounding rock, the mechanical model of the roof and rib support structure is established, and the influence mechanism of the automatically formed roadway parameters on the compound force is revealed. On this basis, the roof and rib support structure technology of confined lightweight concrete is proposed, and its mechanical tests under different eccentricity are carried out. The results show that the bearing capacity of confined lightweight concrete specimens is basically the same as that of ordinary confined concrete specimens. The bearing capacity of confined lightweight concrete specimens under different eccentricities is 1.95 times higher than those of U-shaped steel specimens. By comparing the test results with the theoretical calculated results of the confined concrete, the calculation method of the bearing capacity for the confined lightweight concrete structure is selected. The design method of confined lightweight concrete support structure is established, and is successfully applied in the extra-large mine, Ningtiaota Coal Mine, China.

In this study, the dynamic stress concentration factors (DSCF) around a straight-wall arch tunnel (SWAT) were solved analytically utilizing the complex variable function methods and Duhamel’s integral. The effects of wavelength, incident angle, and blasting rising time on the DSCF distribution were analyzed. Theoretical results pointed out dynamic disturbances resulting in compressive stress concentration in the vertical direction and tensile stress in the incident direction. As the wavelength and rising time increased, there was a tendency for the amplitude of stress concentration to initially rise and then converge. Moreover, a series of 3D FEM models were established to evaluate the effect of different initial stress states on the dynamic failure of the tunnel surrounding rock. The results indicated that the failure of the surrounding rock was significantly influenced by the direction of the static maximum principal stress and the direction of the dynamic disturbance. Under the coupling of static and blasting loading, damage around the tunnel was more prone to occur in the dynamic and static stress concentration coincidence zone. Finally, the damage modes of rock tunnel under static stress and blasting disturbance from different directions were summarized and a proposed support system was presented. The results reveal the mechanisms of deep-buried rock tunnel destruction and dynamically triggered rockburst.

Frothers facilitate the reduction of bubbles size by preventing bubbles coalescence and produce more stable froths. The collision probability of the bubbles and particles substantially increases by decreasing bubble size. For the same volume system, fewer bubbles result from a distribution of large-sized bubbles, and more bubbles result from a distribution of small-sized bubbles. In this research, fundamental two-phase frother characterization parameters were aimed to link with three-phase coal and talc flotation behavior. For this purpose, the effect of single and dual frother systems on inhibiting bubble coalescence was investigated with methyl isobutyl carbinol (MIBC), isooctanol (2 ethyl hexanol), pine oil, and Dowfroth 250. Based on the results of single frothers, isooctanol at the lowest critical coalescence concentration (CCC) value of 6×10⁻⁶ achieved the smallest bubbles with Sauter mean diameter of 0.80 mm. By blending Dowfroth 250 and pine oil, the bubbles size decreased significantly, reaching 0.45 mm. While the highest recoveries in coal flotation were obtained in single and frother blends where the bubbles size was measured as the smallest in two-phase system, and such a relationship was not found for talc flotation.

Water-coupled charge blasting is a promising technique to efficiently break rock masses. In this study, numerical models of double boreholes with water-coupled charge are established using LS-DYNA and are calibrated by the tests of rock masses subjected to explosion loads to examine its performance. The crack levels of rock mass induced by water-coupled charge blasting and air-coupled charge blasting are first compared. It is found that water-coupled charge blasting is more appropriate to fracture deep rock mass than air-coupled charge blasting. In addition, the effects of rock properties, water-coupled charge coefficients, and borehole connection angles on the performance of water-coupled charge blasting are investigated. The results show that rock properties and water-coupled charge coefficients can greatly influence the crack and fragmentation levels of rock mass induced by water-coupled charge blasting under uniform and non-uniform in-situ stresses. However, changing borehole-connection angles can only affect crack and fragmentation levels of rock mass under non-uniform in-situ stresses but barely affect those under uniform in-situ stresses. A formula is finally proposed by considering the above-mentioned factors to provide the design suggestion of water-coupled charge blasting to fracture rock mass with different in-situ stresses.

The study investigated the application of radiofrequency (RF)-sputtered TiO₂ coatings at various temperatures to enhance the hydrophobicity and corrosion resistance of Al6061 alloy. The research aimed to establish a correlation between the coating process and the resulting surface properties. Surface roughness and wettability were quantified with a surface profilometer and goniometer. Additionally, chemical boiling and salt spray corrosion tests were conducted to evaluate any topographical changes during these procedures. The analysis further involved the use of field-emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD) techniques to characterize the deposited coatings. The findings indicated that the TiO₂ coating applied at 500 °C exhibited the highest water contact angle and superior corrosion resistance compared to other temperatures. Surface characterization confirmed that this specific TiO₂ coating at 500 °C effectively delays corrosion due to its hydrophobic behavior, making it durable for industrial applications.

A comprehensive understanding of the dynamic frictional characteristics in rock joints under high normal load and strong confinement is essential for ensuring the safety of deep engineering construction and mitigating geological disasters. This study conducted shear experiments on rough rock joints under displacement-controlled dynamic normal loads, investigating the shear behaviors of joints across varying initial normal loads, normal loading frequencies, and normal loading amplitudes. Experimental results showed that the peak/valley shear force values increased with initial normal loads and normal loading frequencies but showed an initial increase followed by a decrease with normal loading amplitudes. Dynamic normal loading can either increase or decrease shear strength, while this study demonstrates that higher frequencies lead to enhanced friction. Increased initial normal loading and normal loading frequency result in a gradual decrease in joint roughness coefficient (JRC) values of joint surfaces after shearing. Positive correlations existed between frictional energy dissipation and peak shear forces, while post-shear joint surface roughness exhibited a negative correlation with peak shear forces through linear regression analysis. This study contributes to a better understanding of the sliding responses and shear mechanical characteristics of rock joints under dynamic disturbances.

Roof disaster has always been an important factor restricting coal mine safety production. Acidic effect can reform the rock mass structure to weaken the macroscopic strength characteristics, which is an effective way to control the hard limestone roof. In this study, the effects of various factors on the reaction characteristics and mechanical properties of limestone were analyzed. The results show that the acid with stronger hydrogen production capacity after ionization (pK_a<0) has more prominent damage to the mineral grains of limestone. When pK_a increases from −8.00 to 15.70, uniaxial compressive strength and elastic modulus of limestone increase by 117.22% and 75.98%. The influence of acid concentration is manifested in the dissolution behavior of mineral crystals, the crystal defects caused by large-scale acid action will lead to the deterioration of limestone strength, and the strength after 15% concentration reformation can be reduced by 59.42%. The effect of acidification time on limestone has stages and is the most obvious in the initial metathesis reaction stage (within 60 min). The key to the strength damage of acidified limestone is the participation of hydrogen ions in the reaction system. Based on the analytic hierarchy process method, the influence weights of acid type, acid concentration and acidification time on strength are 24.30%, 59.54% and 16.16%, respectively. The research results provide theoretical support for the acidification control of hard limestone roofs in coal mines.

Running safety assessment and tracking irregularity parametric sensitivity analysis of high-speed maglev train-bridge system are of great concern, especially need perfect refinement models in which all properties can be well characterized based on various stochastic excitations. A three-dimensional refined spatial random vibration analysis model of high-speed maglev train-bridge coupled system is established in this paper, in which multi-source uncertainty excitation can be considered simultaneously, and the probability density evolution method (PDEM) is adopted to reveal the system-specific uncertainty dynamic characteristic. The motion equation of the maglev vehicle model is composed of multi-rigid bodies with a total 210-degrees of freedom for each vehicle, and a refined electromagnetic force-air gap model is used to account for the interaction and coupling effect between the moving train and track beam bridges, which are directly established by using finite element method. The model is proven to be applicable by comparing with Monte Carlo simulation. By applying the proposed stochastic framework to the high maglev line, the random dynamic responses of maglev vehicles running on the bridges are studied for running safety and stability assessment. Moreover, the effects of track irregularity wavelength range under different amplitude and running speeds on the coupled system are investigated. The results show that the augmentation of train speed will move backward the sensitive wavelength interval, and track irregularity amplitude influences the response remarkably in the sensitive interval.