Based on the spiral cutting pick cutting and crushing method, the cutting and crushing behavior of spiral drum cutting picks on the ore body and the cutting and crushing process were analyzed, and a dynamic model for ore body cutting and crushing based on pick cutting had been constructed. Based on the HMB contact model in EDEM, a simulation model of cutting picks cutting cobalt-rich crust ore bodies was established, a test platform for simulating ore body crushing was prepared, and verification tests on the cutting and crushing force characteristics of single-tooth and full-tooth cutting were carried out. Test and simulation results are basically consistent in overall trends. In the single-tooth spiral drum test, when the cutting speed increases from 0.05 m/s to 0.1 m/s, the cutting resistance increases by 12.2％. In the full-tooth spiral drum test, when the cutting depth increases from 10 mm to 30 mm, the cutting resistance increases by 110％, and the load fluctuation coefficient increases by 43.4％. With the vibration excitation-assisted crushing method, when the cutting depth is 20 mm and 30 mm, the cutting resistance decreases by 16％ and 10％ respectively. When the cutting depth is 30 mm, the load fluctuation coefficient increases by 16.7％. Test results show that compared with cutting speed, cutting resistance is more sensitive to cutting depth. The greater the cutting depth or the faster the cutting speed, the greater the load fluctuation. The adoption of the vibration excitation-assisted crushing method helps reduce the required cutting force, but the cutting vibration intensifies. The research results can provide technical support for the study on operating parameters of the cutting and crushing technology for deep-sea cobalt-rich crusts and the development of crushing heads.

Revealing the distribution of abutment pressure in the superimposed affected area of goaf is the basis for carrying out the prevention and control of rock burst during excavation in this area. Taking the excavation of the 71330 track roadway in Tianchen Coal Mine as the engineering background, the spatial structure of overlying rock and the evolution characteristics of abutment pressure in the superimposed affected area of goaf were studied through theoretical analysis and numerical simulation. Corresponding countermeasures for prevention and control of rock burst were proposed, and these countermeasures were verified through on-site monitoring data. The results show that a single goaf forms an U-shaped spatial structure of overlying rock, with a relatively low degree of vertical stress concentration. When there are multiple goafs, a S-shaped spatial structure of overlying rock is formed on one side, and the degree of vertical stress concentration in its superimposed affected area is relatively high. During the excavation in the superimposed affected area of goaf, the degree of vertical stress concentration increases further. Adopting the “release-cutoff-reduction-impact resistance” countermeasures has achieved effective prevention and control of rock burst during excavation in the superimposed affected area of goaf. Microseismic events show the characteristic of “high frequency and low energy”. The load of anchor bolt (cable) to support roadway surrounding rock is lower than its fracture limit, and the observation value of the roadway side stress tends to be stable 30 days after point layout. The research results can provide a reference for the prevention and control of rock burst under similar conditions.

To investigate the damage effect of fractured rock masses in deep geothermal high-temperature environment, gneiss was taken as the research object, and micro CT scanning was carried out to obtain the micro-fracture evolution characteristics of rocks under geothermal high-temperature action. Combined with three-dimensional seepage simulation and uniaxial compression test, the permeability performance and strength degradation law were analyzed. The results indicate that geothermal high-temperature effects can cause structural damage to rock masses. As the heat treatment temperature increases from 25 ℃ (untreated) to 800 ℃, the quality loss rate of gneiss specimens rises from 0.181％ to 1.767％, the strength decay rate reaches 34.81％, and the surface porosity increases from 1.74％ to 6.28％. As the heat treatment temperature increases, the porosity of gneiss specimens gradually rises, and the non-uniformity of pore distribution intensifies. The non-connected pores within the rock continuously expand and interconnect, while the volume proportion of connected fractures significantly increases. The formation, propagation, and interconnection of thermal fracture surfaces caused by thermal damage effects adversely impact the impermeability and load-bearing performance of gneiss specimens. Given the multi-scale damage effect caused by geothermal high-temperature environment on deep rock masses, effective fracture sealing measures must be implemented in practical engineering to ensure the safe operation of deep mining.

Aiming at the efficient rock breaking technology and theoretical challenges faced by the full section tunnel boring machine (TBM) under complex conditions of deep underground high confining pressure, systematically explorations of the energy evolution and dissipation characteristics of TBM dual disc cutters for rock breaking in deep ground were obtained. Based on Abaqus nonlinear finite element software, a numerical model of dual disc cutters for intrusion rock breaking was constructed to analyze the damage and energy evolution characteristics of rock mass under variable confining pressure conditions. The effects of confining pressure, uniaxial compressive strength of rock, disc cutter blade width, and disc cutter spacing on energy dissipation of rock mass were studied. The research results indicate that confining pressure significantly changes the damage and failure mode of rock mass. When the confining pressure is low, longitudinal damage development is dominant in the rock mass, and increasing confining pressure promotes lateral damage development, resulting in tensile shear composite fracture. When the confining pressure is 25 MPa, the energy sudden change dissipation rate reaches its peak and enters the energy stable dissipation stage at the earliest. The compressive strength of rocks is nonlinearly correlated with energy dissipation. When the penetration is greater than 1 mm and the compressive strength of rocks is 105 MPa, the energy dissipation rate is the lowest. Under this condition, rocks are prone to breakage. Under high penetration conditions, increasing the disc cutter blade width and disc cutter spacing can promote energy release within the rock mass and improve TBM excavation efficiency. The research results can provide theoretical basis for energy-saving and efficiency improvement of TBM excavation in deep engineering.

Ensuring the stope stability is the foundation for the efficient and safe extraction of broken and thick ore bodies. Taking the mining of a broken and thick ore body in a certain mine as the engineering background, researches were conducted on optimizing the structural parameters of the stope during the orebody mining process using the downward wall filling mining method. The influences of drift dimensions, drift layout patterns, and filling frequencies on stope stability were analyzed in detail from three perspectives of principal stress, vertical displacement, and plastic zone. The findings indicate that the principal stress in the roof of the excavation zone exhibits an approximately uniform distribution, with the minimum principal stress showing tensile stress in the hanging wall and adjacent areas, while the maximum principal stress remains compressive. The central roof of the stope experiences the greatest settlement, while significant settlement is also observed in the hanging wall area, with no settlement but slight bulging in the footwall. The recommended optimal structural parameters are as follows, drift dimensions of 3.0 m×3.0 m, a vertical cross-shaped layout of drift, and a full-height filling process. Industrial trials demonstrate that this optimized solution can control the loss and dilution rate of the stope to approximately 5％, with mining costs maintained at 150 yuan per ton. The resource recovery efficiency and economic benefits are effectively enhanced, providing reliable technical support for subsequent safe and efficient mining operations in the mine.

To investigate the influence of the brow line damage scale on the ore drawing effect, based on the random medium ore drawing theory, a single-segment end ore drawing model was established using the physical similarity test method. The ore drawing test under the brow line damage was carried out from the two scales of the brow line damage width and height. The development law of the draw-out body under different test parameters was determined by the hole-reach method, and the ore drawing loss and dilution index was calculated. The results show that under the same cut-off grade drawing conditions, with the increase of the brow line damage width, the profile width of the drawn body in the direction of the mining approach increases significantly, while the profile width of the drawn body in the direction perpendicular of the mining approach does not change significantly. For every 0.5 m increase in the brow line damage width, the proportion of front waste rock increases by an average of 1.2 percentage points, the proportion of top waste rock decreases by an average of 0.5 percentage points, and the ore recovery rate decreases by an average of 0.6 percentage points. When the brow line damage height increases, the development direction of the drawn body is mainly in the vertical direction, and the shape of the drawn body is more slender. For every 0.5 m increase in the brow line damage height, the proportion of front waste rock decreases by an average of 0.2 percentage points, the proportion of top waste rock increases by an average of 3.9 percentage points, and the ore recovery rate decreases by an average of 5.0 percentage points. The influence of the brow line damage height on the ore drawing effect is significantly higher than that of the brow line damage width. Therefore, in engineering practice, priority should be given to taking measures to avoid and reduce the damage of brow line in the height direction.

The form and thickness of isolation pillars in transition areas are crucial to the safety and efficiency of mine production during the transition from caving mining to filling mining. Taking the mine production of a gold mine in the transition stage from caving mining to filling mining as the background, a scheme of combined setting of pot-bottom isolated pillar and horizontal isolated pillar was proposed, and the safe thickness and stability of the combined isolation pillar were analyzed by theoretical calculation and FLAC3D numerical simulation. The results show that the theoretical thickness of the horizontal isolation pillar at the bottom of the combined isolation pillar is 30 m, while the thickness of the pot-bottom isolation pillar is 15 m. Through the calculation of the maximum unbalanced force and excavation convergence balance cost, it is found that the ground pressure activity during the transition from caving mining to filling mining is generally stable. The isolation pillar does not exceed the tensile stress limit during the mining process, and there is no phenomenon of plastic failure penetration. It shows that the isolation pillar has good self-bearing capacity, which ensures the safety of synchronous mining of caving mining to filling mining. The application of the filling method significantly slows down the settlement rate of the ore body and enhances the stope stability. However, it is necessary to be alert to the local plastic failure of the filling body in the side of the stope and the potential landslide risk in the upper part.

To determine the safety pillar thickness and predict dangerous slopes for a mine in transition from open-pit to underground mining, numerical simulation was conducted based on Rhino and FLAC3D software to analyze the safety pillar thickness, the reliability of the mining method, and the slope safety factor after the completion of underground mining. Firstly, the underground mining method was selected based on the occurrence characteristics of the orebody, then, a simplified stope model was established according to the selected mining method, and a relatively conservative safety pillar thickness was determined. Subsequently, the stope was further divided through refined modeling to verify the reliability of the selected mining method. Finally, the potential dangerous slopes were identified using the strength reduction method, and the slope safety factor after the completion of underground mining was determined. The results show that a 30 m thick safety pillar can ensure safe production during underground mining. After the completion of underground mining, the panel remains generally stable, and the selected mining method is reasonable and reliable. The slope safety factor after underground mining is 4, and the relatively dangerous slope is located on the northern side of the central part of the final pit boundary.

In the downward drift filling mining method, the roof backfill is usually divided into a bearing layer and a capping layer, and their strength is a key factor to ensure roof stability during the drift mining process. Force analysis was carried out on the downward rectangular drift. Considering that both sides of the drift were backfill, the strengths of the bearing layer and capping layer of the drift backfill were designed respectively by combining the stress solution method for rectangular openings based on complex functions with the unconfined compressive deformation test and shear strength test of backfill. An on-site industrial application was carried out in a metal mine in Yunnan to verify the rationality of the designed strength. The results show that when the lateral pressure coefficient of the backfill is 0.29, and the height-width ratio of the rectangular roadway is set to 1.0, the tensile strength of the bearing layer is designed as σ_t＝0.26 MPa and the compressive strength of the capping layer as σ_c＝2.88 MPa with a safety factor of f＝1.5. During the mining and filling process of the underground stope, no phenomena of lateral collapse of the backfill or roof caving are observed. The designed strength meets the requirements of on-site safe operation, and it is estimated to save the mine a filling cost of 5.58 million yuan per year.

Taking the ultra-fine mine tailings as the experimental research object, the optimum mass concentration of the slurry under the conditions of gravity flow and pumping was explored through slump tests, strength ratio tests and response surface analysis. The key factors affecting the compressive strength of the backfill were analyzed, and the NGO-BP neural network model was used to predict the strength of the specimen. The results show that the optimum mass concentration is about 74％ when the pump pressure is transported, and the optimum mass concentration is about 70％ when the gravity flow is transported. When the cement-sand ratio is 1:4, 1:6, 1:8 and 1:20, the 7 d strength of the backfill at each mass concentration reaches 0.8 MPa, and the 28 d strength reaches 1.5 MPa, which meets the strength requirements. When the cement-sand ratio remains unchanged, the strength of the specimen will increase with the increase of mass concentration and the extension of curing age. When other variables remain unchanged, the effect of cement-sand ratio on the strength of the specimen is particularly obvious. The higher the cement-sand ratio, the higher the strength of the specimen. The average absolute error (MAE), average relative percentage error (MAPE), mean square error (MSE), root mean square error (RMSE) predicted by NGO-BP neural network decreases by 0.47, 0.70, 0.96, 0.66, respectively, and the coefficient of determination (R²) increases by 0.26 compared with BP neural network at 7 d of curing. NGO-BP neural network model can be used to guide the filling ratio of production practice, and provide a new idea for the optimization of filling ratio.