Geohazard Mechanics最新文献

In order to predict the coal outburst risk quickly and accurately, a PCA-FA-SVM based coal and gas outburst risk prediction model was designed. Principal component analysis (PCA) was used to pre-process the original data samples, extract the principal components of the samples, use firefly algorithm (FA) to improve the support vector machine model, and compare and analyze the prediction results of PCA-FA-SVM model with BP model, FA-SVM model, FA-BP model and SVM model. Accuracy rate, recall rate, Macro-F1 and model prediction time were used as evaluation indexes. The results show that: Principal component analysis improves the prediction efficiency and accuracy of FA-SVM model. The accuracy rate of PCA-FA-SVM model predicting coal and gas outburst risk is 0.962, recall rate is 0.955, Macro-F1 is 0.957, and model prediction time is 0.312s. Compared with other models, The comprehensive performance of PCA-FA-SVM model is better.

The problem of repeated immersion-induced fatigue damage in engineering coal measures sedimentary rock, including coal-rock pillars, reservoir bank slopes, and water-rich tunnels at the boundary of coal mine underground reservoirs, has profound implications for their stability, safety, and operation, and can even lead to geological disasters. To address this issue, this paper aims to construct a constitutive model that accurately captures the comprehensive process of deformation and failure in water-bearing coal measures sedimentary rock. It explores the deformation characteristics of these formations and provides a theoretical foundation for numerical simulations of geological disasters induced by water-rock interaction. This study integrates the deformation mechanisms of void and matrix deformation in coal seam sedimentary rocks, while considering the influence of immersion cycles. Subsequently, it formulates a segmented constitutive model to depict the entire process of deformation and failure in cyclically immersed water-bearing coal measures sedimentary rock under uniaxial compression. The proposed model's accuracy and rationality are validated through comparisons with experimental research findings and existing theoretical curves from similar models. The results demonstrate the model's effectiveness in describing the deformation behavior of non-dense water-bearing coal measures sedimentary rock under uniaxial compression or low confining pressure before reaching peak stress, although further refinements may be necessary to precisely capture post-peak deformation characteristics. Model parameters, including the deformation caused by voids (γ₀) between voids, increase exponentially with immersion times, while the elastic modulus (E_v) of voids and the parameter (F₀) related to the average strength of microelements decrease exponentially. The homogeneity degree (m) exhibits no discernible pattern. These research outcomes provide valuable insights for the stability control of engineering coal measures sedimentary rock under water-rock interaction and the mitigation of related geological disasters.

The replacement ratio is an essential factor in evaluating the bearing capacity characteristics of composite foundations. This study focuses on the bearing capacity of a pervious concrete pile with different replacement ratios. The axial force, skin friction, and settlement were evaluated using a model test to assess the performance of the pervious concrete pile composite foundation. When the replacement ratio was reduced from 9.26% to 2.32%, the characteristic bearing capacity value was only 14%. Therefore, it may be unreasonable to use the settlement ratio method to evaluate this composite foundation's bearing capacity in a model test. Appropriate loading can significantly improve the bearing capacity of a pervious concrete pile composite foundation with a low replacement ratio. The pile–soil stress ratio exhibited different decreasing ranges in the later loading stage. As the load increased, the axial force of the pervious concrete piles was small and nonobvious, and the average side friction resistance of the piles in the foundation with a lower replacement ratio slowly increased.

Coal bump seriously threatens the safe and efficient mining of coal, and the research on the occurrence mechanism of coal bump is of great significance. The roadway coal bump accounts for 86.8% of the total. The occurrence of coal bump in gateroad is summarized. It is considered that hard roof and hard coal are the geological characteristics of coal bump, and the sliding instability of rib coal mass is the failure characteristics of coal bump. Based on the elastic foundation theory, the upward deflection characteristics of the front and lateral roof of the working face under the condition of hard roof are analyzed, and compared with the engineering practice of roof rebounding. Taking the roadway coal mass as the research object, the unloading sliding mechanical model of roof-coal-floor composite structure is established. By analyzing the relationship between horizontal ground stress of coal mass, frictional force of coal-roof and coal-floor and tensile resistance of coal mass, the critical equation of coal bump is established. It is proposed that the vertical pressure of coal seam is reduced due to the upward deflection of the roof, and the coal mass loses its clamping and moves into the roadway after overcoming the friction between roof and floor and the tensile strength of coal mass under the action of horizontal ground stress, that is, the unloading and slippage mechanism of coal bump in hard roof mining roadway. The model reasonably explains the causality of coal bump in hard roof mining roadway. Based on the unloading-slippage model, the principle of influencing factors of coal bump, includes the buried depth, roof strength, roof elastic modulus and roof thickness, coal mass strength and elastic modulus. Finally, two coal bump events, ''8.2'' coal bump in Tangshan coal mine and ''11.11'' coal bump in Hongyang mine are analyzed and the unloading-slippage mechanism are the reasoning of two events.

The freezing and expansion diseases of railroad roadbeds are prevalent in areas that experience seasonal freezing. This study aims to investigate the features of the freezing and expansion mechanism of seasonal frozen railroad roadbeds and the effects of the freezing and expansion diseases on the roadbeds. This article presents a study of the Shuo-Huang Heavy Duty Railway. Initially, on-site monitoring tests were conducted to analyze the roadbed temperature, water content and deformations due to freezing. Through these tests, the pattern of development of the roadbed freezing and swelling was understood, and the effect of this on the vibration response of the roadbed was investigated. Subsequently, load-free freezing tests were performed to investigate the freezing and expansion features of the roadbed. Through on-site monitoring, it has been determined that the seasonal freezing layer is approximately 0.5 ​m deep. The depth of the frozen expansion on both sides of the road shows clear differences. The frozen and expansion disease significantly amplifies the vibration acceleration of the roadbed, with a tendency towards low-frequency and high-amplitude vibrations. Through indoor testing, we compared the deformation of frozen specimens and their final freeze and expansion rates at different cold-end temperatures and various initial moisture content levels. We find that the initial moisture content has a greater impact on specimen freezing and expansion. The findings in this paper can be used as a reference for researching and addressing roadbed freezing and expansion problems.

Geological hazards caused by high-temperature rocks cooling down after encountering water are closely related to underground mining and tunneling projects. To fully understand the impact of temperature changes on the mechanical properties of rocks, yellow rust granite samples were subjected to heating-natural cooling and heating-water cooling cycles to experimentally study the effects of these processes on the mechanical properties of the samples. The mechanism of the heating-cooling process on the macromechanical properties of the rock was discussed. Based on the Drucker-Prager criterion and Weibull distribution function, a damage variable correction factor was introduced to reflect the post-peak strain softening characteristics, and a thermo-mechanical coupled damage constitutive model of the granite was established. The results showed that in the natural cooling mode, the mechanical properties deteriorate significantly when the temperature exceeded 600 ​°C, and the failure mode changed from brittle failure to ductile failure. In the water cooling mode, the peak strength and deformation modulus increased at temperatures below 400 ​°C with an increase in the cycle number, while at 600 ​°C, the peak strength and elastic modulus notably decreased. The peak strain increased with the increase of the cycle number and temperature at all temperatures, and the failure mode of the granite tended to change from tensile failure mode to shear failure mode. The experimental results were used to validate the damage constitutive model. The shape parameter r and scale parameter S in the Weibull distribution function of the model were used as indicators to reflect the brittleness degree and peak strength. This study helps to understand the behavior of rocks in high-temperature environments, in order to prevent and mitigate potential geological hazards.

The paper describes the research findings on georadar detection of hydraulic fractures in hydrocarbon reservoirs. Numerical and physical modeling enables studying effect exerted by the electromagnetic properties of the created fracture fill and by the properties of the enclosing formation on the coefficient of high-frequency EM wave reflection from the interface.

In this paper, how to determine the Weibull modulus of a fracture strength distribution is discussed with its physical implications for quasi-brittle materials. Based on the Markov chain assumption, it is shown that the lifetime (i.e., the time taken for formation of a critical defect) in a quasi-brittle material can be described by a gamma probabilistic distribution function. Prior to macroscopic failure, the effective number of energy barriers to be overcome is determined by the slope of the energy barrier spectrum, which is equivalent to the Weibull modulus. Based on a fracture mechanics model, the fracture energy barrier spectral slope and Weibull modulus can be calculated theoretically. Furthermore, such a model can be extended to take into account the crack interactions and defect-induced degradation. The predicted Weibull modulus is good agreement with that derived from available experimental results.

The article focuses on a theoretical and experimental framework for the quantification of interaction between nonlinear geomechnical and physicochemical processes in high-stress coal-bearing rock mass during mining under high seismic risk due to large-scale blasting and earthquakes, as well as because of structural and temperature effects. The tests were aimed to examine and study comprehensively the piston mechanism of gas exchange and mass transfer processes, revealed recently at the Institute of Mining, SB RAS, as well as to explain the fact that the earthquake-induced low-velocity (quasi-meter range) pendulum waves (velocity to 1 ​m/s and frequency of 0.5–5 ​Hz) could stimulate an increase in the gas content in coal mines. In order to perform laboratory investigation at the Institute of Mining SB RAS, special-purpose stand for analyzing gas exchange and mass transfer processes in coal-bearing geomaterials under various thermodynamic conditions (P, V, T) and gas composition was constructed in cooperation with the Institute of Semiconductors Physics SB RAS. Matching of air flow rate with compression pressures allowed to obtain relations showing that air flow rate increases at the uncertain time interval under the increasing of the compression pressure. The same measurements was carried out with another gases such as Hydrogen H₂, Helium He, methane CH₄, carbon dioxide CO₂ and carbon oxide CO. The laboratory tests aimed to detailed investigation of the previously revealed “piston mechanism” of gas exchange and mass transfer processes in the coal specimens and their quantitative description in terms of theory of the pendulum waves were carried in the first time. Consequently, there are some arguments for the testing of the opportunity of quantitative description of the “piston mechanism” related to gas exchange and mass transfer processes in the scale of coal mines. It is relevant when pendulum waves induced by powerful earthquakes and technical blasting reaches the mine.

Destruction of reinforced concrete (RC) structures, particularly non-ductile RC structures, in recent earthquakes demonstrate their vulnerability under lateral forces generated in an earthquake. Despite the extensive literature on the subject and the wide variety of strengthening techniques available, there is no consensus on the efficiency of these techniques in improving the seismic performance of RC structures. In this study, a five-storeyed RC-framed building is considered to evaluate its seismic performance through static non-linear pushover analysis. To examine the effect of various cases encountered in practice, the pushover analysis is carried out on the RC frame for various cases, i.e. a bare RC frame, an RC frame with masonry infills but with an open ground storey, and RC frames with shear walls with a variety of thicknesses and steel reinforcement ratios. Further, to investigate the effect of retrofitting, the RC frame is strengthened using local jacketing and bracings. From the results, it is observed that the initial stiffness and base shear of masonry infilled RC frame with an open ground storey exhibit an increase of 2.6%, and 19%, respectively, as compared to the bare frame. The use of shear walls increases the initial stiffness and base shears, and they increase by 6–14% and 8–20%, respectively, with an increase in the reinforcement ratio in the shear wall. Retrofitting with the use of both diagonal bracings causes the base shear to increase by a factor of 7.7 as compared to that of the open ground storey. Finally, the probability of damage to the RC frame in all cases was compared using seismic fragility curves.