Investigation of Deep Shaft-Surrounding Rock Support Technology Based on a Post-Peak Strain-Softening Model of Rock Mass

To control the large deformation that occurs in deep shaft-surrounding rock, the post-peak strain-softening characteristics of deep jointed rock mass are discussed in detail. An equivalent post-peak strain-softening model of jointed rock mass is established based on continuum theory and the geological strength index surrounding rock grading system, and numerical simulations are performed using FLAC3D software. The convergence-constraint method is used to analyze the rock support structure interaction mechanism. A composiste support technique is proposed in combination with actual field breakage conditions. During the initial support stage, high-strength anchors are used to release the rock stress, and high-stiffness secondary support is provided by well rings and poured concrete. This support technology is applied in the accessory well of a coal mine in Niaoshan, Heilongjiang, China. The stability of the surrounding rock support structure is calculated and analyzed by comparing the ideal elastic-plastic model and equivalent jointed rock mass strain-softening model. The results show that a support structure designed based on the ideal elastic-plastic model cannot meet the stability requirements of the surrounding rock and that radial deformation of the surrounding rock reaches 300 mm. The support structure designed based on the equivalent joint strain-softening model has a convergence rate of surrounding rock deformation of less than 1 mm/d after 35 days of application. The surrounding rock deformation is finally controlled at 140 mm, indicating successful application of the support technology.

Study and evaluation of the stability of underground mining method used in shallow-dip vein deposits hosted in poor quality rock

Purpose.This article proposes to analyze and determine the mining design for shallow-dip deposits hosted in poor quality rock. Methods. We used the UBC tool to find the optimal exploitation method, the Rock mass rating (RMR) and Q-system (Q) to determine the optimal mining stope and the recommended rock support, the numerical modeling by RS2 software with a variety of geotechnical, geometrical, and technical conditions to analyze the evolution of the unstable zone width and the maximum total displacement around the stope after excavation. Findings. The optimum mining method designated by the UBC tool for this type of deposit is the cut and fill. By projecting the obtained RMR and Q-system values on the design graph, it is concluded that the operating stope is located in the stable zone with a height of 3 m, and bolting support is recommended. The simulation by RS2 software reveals that the optimal mining design that can be used to mine shallow-dip vein deposits hosted in poor quality rocks consists of a 3 m high stope and a 75° dip with cemented backfill. Originality.This work presents a study to choose the most suitable underground mining method and mine design for shallow-dip deposits hosted in poor quality rock. Practical implications.In the mining industry, the success of operating an underground mine is conditioned by the selection of the appropriate method, of the mining design and dimensioning of a rock support adapted to the nature of the rock, and excavation geometry according to the type and nature of the deposit.

The Relationship between Mining-Induced Stress and Coal Gas under an Optimized Support Scheme: A Case Study in the Guanyinshan Coal Mine, China

Stress is one of the main factors influencing coal and gas outbursts. The apparent effects of the crustal stress, the structural stress, and the mining-induced stress increase as the depth of mining increases. At present, there have been few studies of the relationship between the comprehensive analyses of the crustal stress, mining-induced stress, and coal gas. The in situ measurement of the relationship between stress-related behaviors and coal gas under the influence of mining was conducted through experimental analysis of surrounding rock support and coal and gas outburst control and optimization of surrounding rock support materials and system construction. The results showed that the mining-induced stress first increased to a peak value, then gradually decreased, and tended to stabilize as the footage progresses. Stress appears at 96 m ahead due to mining; after 57 m of advancing, there is a large increase until it passes through this area. The stress in front of the working face increases linearly, and the increase range is obviously larger than that of the coal body in a certain range on both sides. The support anchoring force gradually decreased and tended to be stable after rapidly increasing to a maximum value. The deep displacement of the roof increased linearly and tended to be stable after reaching an accumulated displacement which can reach 16-28 mm. The residual gas pressure in front of mining operations decreased rapidly, and beyond 15 m on each side of the roadway, it decreased significantly. The residual gas pressure and gas content were consistent with the gas desorption index of drill cuttings due to the influences of gas predrainage and mining. The stress along the direction of the roadway and the residual gas content, the residual gas pressure, and the gas desorption index of drill cuttings conform to the logarithmic functional relationship. The research results provide a basis for the comprehensive prevention and control of coal and gas outbursts from multiple angles considering stress, coal, and gas.