Rock breaking is one of the most basic issues in deep underground engineering. Water plays an important role in the rock response under microwave radiation. Consequently, microwave radiation experiments using red sandstone with different water contents were conducted. The damage characteristics and ultrasonic properties of red sandstone after microwave radiation were primarily investigated, and the representative conclusions were drawn as follows: With the increase in water content, the time of complete formation of the rupture surface of the rock sample gradually decreased, and the decreasing range gradually increased. When the fracture surface is completely formed, the samples with a higher water content have more powdery rock cuttings and less surface roughness. The damage degree of the samples does not increase significantly with the increase in the water content when the sample is radiated at the same time. As the microwave radiation time is increased, the damage degree of the sample will increase significantly. Through the ultrasonic velocity test, it can be suggested that the sample exhibits obvious zonal damage characteristics under the action of a microwave. Generally speaking, it is a very effective means of improving the degree of microwave attenuation of the rock by increasing the water content of the rock mass.

Deep brittle rock exhibits characteristics of rapid stress dropping rate and large stress dropping degree after peak failure. To simulate the whole process of deformation and failure of the deep brittle rock under load, the Lemaitre strain equivalent theory is modified to make the damaged part of the rock has residual stress. Based on the damage constitutive model considering residual strength characteristics, a correction factor reflecting stress dropping rate is added, the Weibull distribution is used to describe the inhomogeneity of rock materials, and Drucker–Prager criterion is used to quantitatively describe the influence of stress on damage; a damage constitutive model of deep brittle rock considering stress dropping characteristics is established. According to the geometric features of the rock stress‐strain curve, the theoretical expressions of model parameters are derived. To verify the rationality of the model, triaxial compression experiments of deep brittle rock under different confining pressures are conducted. And the influence of model parameters on rock mechanical behaviour is analysed. The results show that the model reflects the stress dropping characteristics of deep brittle rock and the theoretical curve is in good agreement with the experimental results, which indicates that the proposed constitutive model is scientific and feasible.

The basic premise of deep in situ fluidized mining is to study the in situ stress state of deep rocks, and coring is one of the basic physical means. However, core discing often occurs in the process of coring. And core discing is one of the symbols of high in situ stress in deep engineering area, and revealing the mechanical response of core stub under different conditions is an important premise to explore the formation mechanism of core discing. Therefore, the effects of in situ stress combination condition, core diameter, and drilling depth on the maximum tensile stress after core stub unloading are discussed by PFC^2D discrete element numerical simulation method, and the formation mechanism of core discing is preliminarily explored based on strain energy and dissipated energy. Research shows that in situ stress combination is the most dominant factor of core discing. When the hydrostatic stress increases from 40MPa to 80MPa, the maximum tensile stress at the core stub increases by 98.42. When the horizontal stress is 60MPa and the axial stress increases from 40MPa to 100MPa, the maximum tensile stress at the core stub increases by 53.33. However, when the axial stress is 60MPa and the horizontal stress increases from 40MPa to 80MPa, the maximum tensile stress at the core stub first increases and then decreases, and there is an inflection point when the horizontal stress is 75MPa. When the core diameter increases from 8.00mm to 13.00mm, the maximum tensile stress at the core stub increases by 1.58 times. When the drilling depth increases from 3.00cm to 4.00cm, the maximum tensile stress at the core stub increases by 4.01 times; that is, small diameter cores and cores with large drilling depth are more prone to core discing. The total energy of the system increases with the increase of in situ stress. When the hydrostatic pressure is 80MPa, the dissipated energy of the system is 2.80 times greater than that when the hydrostatic pressure is 40MPa. More energy must be dissipated when the core discing occurs under higher in situ stress conditions. It is preliminarily proved that the formation mechanism of core discing is that the tensile cracks extend and penetrate at the core stub, and the core is pulled off to form a core disc, which is reciprocating to produce core discing. The research results are expected to provide a certain reference for understanding the formation mechanism of core discing and provide useful ideas for the related research of discing phenomenon.

In goafs formed by underground mineral resource extraction, the remaining pillars are often subjected to uniaxial loading at different loading rates, and their mechanical responses and failure mechanisms directly affect the long-term stability of the goafs. This study uses rock-like materials to conduct uniaxial compression tests at loading rates ranging from 0.001 mm/min to 0.05 mm/min, combined with acoustic emission (AE) monitoring, to systematically investigate the effects of loading rate on the mechanical properties, energy distribution, constitutive model, and AE characteristics of the material. The results show that an increase in loading rate significantly enhances the stiffness and strength of the material, promotes a transition in failure mode from a shear–tension composite to tension-dominated, intensifies brittle characteristics, and simultaneously inhibits full crack development and fragments generation. In terms of energy evolution, an increased loading rate enhances the pre-peak total strain energy and elastic strain energy storage but reduces the efficiency of energy dissipation, leading to an intensified mismatch between energy storage and dissipation capacities at peak stress. A damage variable induced by loading rate was proposed, and a damage constitutive model considering the loading rate was established, with the theoretical curves showing good agreement with the experimental data. AE characteristic analysis further reveals that an increase in loading rate causes the crack type to transition from shear-dominated to tension-dominated, and the fluctuating increase in the b-value reflects a reduction in pre-peak fracture scale and a decrease in the degree of material fragmentation. The research findings are expected to deepen the understanding of the damage and failure mechanisms of rock materials under different loading rates, thereby laying a research foundation for the stability assessment of goaf pillars and disaster warning.

To address the difficulty of determining the safe reserved thickness of the mining wall in the test block of the panel pillar at Tongkeng Mine, The stress of mining wall is comprehensively analyzed. Combined with numerical simulation method and field monitoring, the optimal wall thickness is determined. By differentiating each stress component, the mathematical equations governing the locations where extreme values of the stress components occur are derived, and the mathematical expressions for the extreme value positions of each stress component are further determined accordingly. Considering the geological characteristics and mining conditions of the experimental stope with panel pillars, the eastern mining wall of the test block is selected as the research object. A mining wall thickness range of 3 m to 8 m is designed, and the optimal safe reserved thickness of the mining wall is determined through numerical simulation. Based on the optimal mining wall retention thickness, stopping operations are carried out on the orebody of the experimental stope. Meanwhile, monitoring points are reasonably arranged from the upper-middle section to the middle of the mining wall, and real-time monitoring is performed on the stress variation data at each monitoring point during the entire stopping process of the test block. Theoretical analysis results show that the exact locations of the extreme values of each stress component can be accurately determined within the two-dimensional plane of the mining wall, among which the extreme value of the horizontal stress component appears at the midpoint of the mining wall thickness. Numerical simulation results indicate that both the stress and displacement of the mining wall exhibit a gradual decreasing trend with an increase in mining wall thickness. However, when the mining wall thickness exceeds 5 m, the reduction rate of stress and displacement slows down significantly, and the mining wall tends to become stable. Maintaining a mining wall thickness of 5 m in the experimental stope can generally ensure the safe recovery of the orebody. However, pronounced stress concentrations occur at the geometric corners of the mining wall, which result from stress retention caused by changes in the mining wall geometry. Meanwhile, the stress concentration in the mining wall is synchronized with that in the drilling galleries of the experimental stope, and varying degrees of failure occur in the drilling galleries at locations where stress concentration appears in the mining wall. Monitoring results show that the maximum stress borne by the drilling gallery is approximately 26 MPa, beyond which rock mass collapse and fragmentation are prone to occur.