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The high geothermal environments encountered in deep mineral mining induce thermal damage to rocks, which can trigger geotechnical disasters in deep engineering projects. Therefore, exploring the degradation characteristics of rock mechanical properties and the damage evolution laws after high-temperature exposure is of significant importance for rock engineering in deep high-geothermal environments. By subjecting granite to the temperature range from ambient to 1200 ℃ and conducting macro-microscopic studies using optical microscopy, the degradation characteristics of Young's modulus and compressive strength in granite samples post various high-temperature treatments were investigated. Additionally, an analysis was performed on the internal cracks and damage evolution in thermally damaged granite from a microscopic perspective. The experimental results demonstrate that high-temperature treatments significantly reduce the mechanical properties of granite. The granite's compressive strength and Young's modulus decrease with increasing treatment temperatures, and the extent of crack development increases with temperature. The mechanic cal properties of granite are highly correlated with the development of internal crack structures. There is a power function relationship between the crack density and compressive strength in granite after different temperature treatments, indicating that crack density can effectively reflect the extent of thermal damage in granite.

In order to improve the recovery rate of coal resources in general, Chengzhuang Coal Mine has carried out and implemented the technology of gob-side entry retaining in 5309 large height mining face. In view of the complex conditions such as 6 m thick coal seam and hard thick rock stratum in the roof, the application of directional blasting presplitting and flexible formwork concrete technology in the mining face of “thick coal seam and hard roof” is emphatically discussed by means of theoretical analysis and field test. The results show that the deformation of gob side entry retaining roadway develops rapidly within 10-90 m behind the working face; the wall pressure of gob-side entry retaining reaches the maximum within 50-100 m behind the working face; the cooperative application of blasting presplitting, roof cutting and pressure relief and flexible formwork concrete wall not only reduces the influence of periodic pressure on the roof of the roadway reserved along the goaf, but also enhances the bearing capacity of the roadway side, which obviously improves the overall stability and reliability of the roadway.

A shallow water wave equation including the famous Degasperis-Procesi model is considered. Firstly, the L2 conservation law for the equation is derived. Secondly, using the methods of transport equation, we establish the boundedness of solutions for the shallow water wave equation. Finally, utilizing the approaches to construct Lyapunov functions, we find local-in-space wave breaking criteria of its solutions on the line $ \mathbb {R} $ R and circle $ \mathbb {S} $ S under certain restrictions on the coefficients of the equation. [ABSTRACT FROM AUTHOR]

Prior to being released, the top coal of a fully mechanized caving face typically experiences the effects of mining-induced pressure and disturbances from the hydraulic support's canopy. To investigate the promoting effect of canopy disturbances in the support-controlled area on the damage of top coal during fully mechanized top-coal caving mining, block instability theory and discrete block numerical simulation methods were employed. The instability modes during the initial support and cyclic disturbance stages were analyzed. The fracture evolution and displacement distribution curves were studied for coal bodies with strengths of 3.1 MPa, 15.0 MPa, and 29.5 MPa under the mining influence and support strengths of 0.5 MPa, 1.0 MPa, and 1.5 MPa during the initial support and cyclic disturbance processes. The results showed that during the initial support stage, the instability of the block-structured coal body exhibited four modes as follows: inter-block breakage, inter-block delamination, intra-block fracture expansion, and inter-block sliding. During the cyclic disturbance stage, the coal body instability showed three modes as follows: inter-block sliding, intra-block fracture expansion, and inter-block rotation. The disturbance from the support had little impact on the fragmentation of both low-strength and high-strength coal bodies. However, small support forces combined with multiple cycles of disturbance had an enhancing effect on the instability of medium-strength block-structured top coal. [ABSTRACT FROM AUTHOR]

With the escalating demand for advanced and eco-friendly processing technologies in mining engineering, the potential applications of microwave heating technology in the treatment of cement tailings backfill (CTB) are expanding significantly. This research comprehensively investigates the mechanisms through which microwave irradiation duration and power influence the mechanical properties of CTB with varying concentrations and cement-to-sand ratios. The aim is to reveal the influencing patterns through experimental methods, providing scientific evidence for optimizing CTB treatment processes. This paper conducted microwave heating tests, uniaxial compression tests, and SEM-EDS tests on CTB. The research results indicate that heating time and power significantly enhance the early strength of CTB, with a more pronounced effect on CTB with higher concentrations and higher cement–sand ratios. When the heating time is 7 min and the heating power is 340 W, the cement hydration reaction is maximally promoted, thereby increasing the density and strength growth rate of CTB. However, excessively long heating time or overly high heating power may cause microcracks or thermal stress concentration within the CTB, adversely affecting the strength growth rate of CTB. Optimal thermal exposure duration and microwave power settings facilitate the activation of cementitious materials and the nucleation of calcium-silicate-hydrate (C-S-H) phases, thereby accelerating the compressive strength evolution of cemented tailings backfill (CTB). The outcomes of this research offer valuable insights into the deployment of microwave heating methodologies in underground mine backfilling, which are pivotal for augmenting the economic viability and environmental sustainability of mining operations. [ABSTRACT FROM AUTHOR]