Key technologies for intelligent, efficient, and safe mining of impact thick coal seams due to hard roof

To address the challenges of source-based rock burst elimination and efficient mining in ultra-thick coal seams prone to rock bursts due to hard roofs, a safety assurance technology was developed to create a favorable environment for intelligent and efficient coal caving. Building on this foundation, breakthroughs in intelligent caving technologies were achieved, resulting in the development of an intelligent top-caving mining system for ultra-thick coal seams with hard roofs. The research process includes the following: For safety assurance in mining ultra-thick coal seams with hard roofs, the Timoshenko beam theory was applied to establish an elastic energy accumulation model for the periodic breakage of hard roofs. This enabled the analysis of energy density distributions under different uniaxial tensile strengths and revealed the advanced rock burst elimination mechanism based on pre-fabricated artificial fracture networks from ground. Accordingly, horizontal well fracturing and liquid explosive blasting techniques were developed, forming ground-based advanced rock burst elimination technology. Furthermore, using Reissner’s thick-plate theory, mechanical models for roof behavior before and after directional fracturing were constructed. These models analyzed the effects of artificial directional fractures on roof elastic energy density and coal static load increments, uncovering the rock burst elimination mechanism of underground artificial directional fractures. Then, a directional composite blasting technology was invented, leading to underground-based advanced rock burst elimination technology. In intelligent mining, several innovations were introduced, including radar-based coal thickness detection, near-infrared spectroscopy for coal-rock identification, vibration and audio-based coal-rock identification, and laser 3D scanning for real-time coal extraction monitoring. These developments formed an intelligent perception and identification technology for top-caving working faces with ultra-thick coal seams. A multi-source information database for intelligent top-caving longwall panels integrating human, machine, and environmental data was established, along with coordinated mining and caving decision-making models and intelligent decision-making technologies for caving processes. High-precision inertial navigation for equipment positioning and a remote communication and control platform were developed, enabling remote intelligent control for top coal caving. Key findings include: ① For tensile strengths of 0.76, 1.57, 2.68, 3.95, and 5.68 MPa, the corresponding peak elastic energy densities of hard roofs were 6.5, 25.4, 71.6, 168.2, and 340.1 kJ/m, respectively, with a quadratic relationship between peak elastic energy density (U^e_max) and tensile strength (σ₀): U^e_max = 10.715σ₀²−0.7182σ₀. ② Artificial fracture networks altered the boundary conditions of hard roofs. For instance, theoretical calculations for the 103_上02 workface of Yanzhou Coal Mining Group showed that artificial fracture networks reduced the first breakage distance of the sandstone layer from 250 m to 123 m. ③ For rock burst elimination mechanism by ground-based artificial fracture networks, numerous fractures created structural weak surfaces in the strata, reducing the elastic energy accumulation in hard roofs and weakening seismic intensity caused by roof ruptures, thereby mitigating rock bursts in workfaces and roadways. For rock burst elimination mechanism by underground artificial directional fractures, directional cracks reduced or eliminated elastic energy near roadways, decreasing the static load increment on the roof-cutting side and effectively controlling rock bursts within roadways.