What new changes have occurred in mining and strata control technology in China? What new progress has been made in deep mining research? What new concepts have emerged in green mining? At the recently held First National Mining & Strata Control Academic Conference, experts and scholars engaged in lively discussions on topics such as safe and green mining and intelligent development in the mining industry.

Significant Achievements in Technological Transformation of Underground Coal Mining

Kang Hongpu, Academician of the Chinese Academy of Engineering and Chief Scientist of China Coal Technology & Engineering Group, pointed out that in recent years, China has achieved remarkable results in the technological transformation of underground coal mining, establishing a group of internationally advanced modern large-scale underground coal mines, forming the world’s largest coal technology and equipment R&D and manufacturing system, and promoting continuous improvement in coal mine safety production.

“For underground coal mines, mining and strata control technology plays a core role,” Kang said. He noted that the key factors affecting coal mining and strata control lie in coal mining processes and equipment, mining face strata control, roadway excavation technology and equipment, as well as roadway surrounding rock control and mining-induced strata control technologies.

In recent years, Kang and his team have proposed a new concept for strata control: applying the “trinity” collaborative control theory of roadway support, modification, and pressure relief to overcome the challenge of controlling large deformations in complex roadways that traditional single support methods cannot address. This technology was validated at the Kouzidong Mine of Zhongmei Xinji Energy, a kilometer-deep mine with soft rock and strong mining-induced stress. Data showed that after applying this technology at Kouzidong Mine, roof subsidence decreased by 74.9%, rib convergence decreased by 72.7%, and large deformation of the surrounding rock was effectively controlled. The breakage rate of bolts and cables decreased by 90%, and overall economic costs were reduced by 23.34%.

In addition to longwall fully mechanized mining, fully mechanized top-coal caving is another major mining method for achieving safe and efficient coal mining in China. In 2024, underground coal mines in China produced 3.6 billion tons of coal, with top-coal caving accounting for about 20%, or nearly 700 million tons.

Mines in China’s main coal-producing regions—Shanxi, Shaanxi, and Inner Mongolia—are characterized by extra-thick coal seams, hard roofs, and large-space mining faces, resulting in complex strata movement and ground pressure behavior, which can easily lead to dynamic disasters such as rock bursts.

“Hard roofs are a challenge in strata control, severely restricting safe, efficient, and intelligent mining,” noted Yu Bin, a professor at Chongqing University.

The main coal seam in the Datong mining area is 20 meters thick, representing a typical hard roof. Combining field measurements of overburden movement and fracture characteristics in large-space conditions with theoretical research on strata control in large-space mining faces, Yu and his team pioneered a ground fracturing control technology for hard roofs in coal mines. By actively weakening and relieving pressure, they achieved effective control of hard roofs, establishing a ground fracturing technology system with coal mine characteristics that supports the intelligent and efficient mining of extra-thick coal seams in the Datong mining area.

“Extra-thick coal seams are the mainstay of efficient mining in China, accounting for over 50%. As coal resource development shifts westward, the leading role of technology in extra-thick coal seam mining is becoming increasingly prominent, with broad development prospects,” Yu said.

Wang Jiachen, a professor at China University of Mining and Technology (Beijing), noted that top-coal caving technology in China is increasingly being applied in complex environments such as “three-soft” thick coal seams, hard thick coal seams, high-gas thick coal seams, and steeply inclined thick coal seams, with wider adaptability in terms of coal seam thickness, inclination, and roof conditions. Today, fully mechanized top-coal caving mining is showing new development trends.

“Intelligent top-coal drawing technology is the core of achieving intelligent top-coal caving mining, but there is no mature experience to draw from; it is pioneering work,” Wang Jiachen explained.

Focusing on the challenges of intelligent top-coal drawing, such as accurately identifying coal and gangue on the rear scraper conveyor and implementing precise control on-site, Wang and his team developed intelligent coal-gangue identification technology, which has been applied at the 81202 working face of Baode Coal Mine under China Energy’s Shendong Coal Company.

In the area of rock burst prevention, Lai Xingping, a professor at Xi’an University of Science and Technology, and his team developed a drilling multi-modal information collection device and a roof full-area attitude monitoring device. Integrating the advantages of ultrasonic, electromagnetic wave, and optical camera detection, they achieved precise extraction of information on coal-rock deformation and instability. Based on this, they developed a full-factor intelligent mine pressure sensing rock burst early warning system, a multi-modal driven rock burst intelligent early warning system, and a ubiquitous intelligent sensing large model for mining-induced surrounding rock instability, achieving informatization in the intelligent sensing and prediction of rock bursts. These technological achievements have helped key coal enterprises and county-level enterprises in Shaanxi Province safely extract 2.05 million tons of coal.

Ju Yang, a professor at China University of Mining and Technology (Beijing), introduced that for the difficult problem of predicting rock bursts induced by fault slip, the digital photoelastic method can be used to track the propagation process of stress waves, visually representing the evolution of dynamic stress fields. Ju and his team developed a transparent analysis experimental system for dynamic stress fields in fault roadway surrounding rock under engineering disturbance. Using a picosecond pulse laser as the light source and a synchronous control scheme combining a high-precision trigger device with a picosecond pulse generator, they achieved synchronous acquisition of photoelastic fringe images throughout the entire impact process. This provides a new method for intuitively and quantitatively revealing the stress propagation laws of complex rock structures under dynamic loading.

New Progress in Deep Mining Research

Currently, China’s mines have entered the deep mining stage, with the deepest reaching 1,510 meters. High ground stress, high temperature, high water pressure, and intense mining disturbances pose significant challenges to safe and efficient mining in deep shafts, necessitating the development of new mining methods for extreme deep environments.

Liu Quansheng, a professor at Wuhan University, stated that the primary hazard in deep mining is meter-level large deformation. Challenges include a lack of understanding of the catastrophe mechanism of meter-level large deformation in deep roadways, the absence of applicable theories and effective technologies for controlling such large deformation disasters, and the lack of safe and efficient roadway formation technologies under deep large-deformation catastrophic environments.

To address these challenges, Liu and his team developed simulation technology for monitoring meter-level large deformation in deep roadways, revealing the mechanism of bulking movement. They also developed a stepwise collaborative control theory and comprehensive technology for bulking large deformation disasters in deep roadways, as well as key technologies for safe and efficient TBM tunneling in deep large-deformation catastrophic environments.

“Focusing on the surrounding rock, through coupling support with the surrounding rock and using multiple methods in stepwise collaboration, we can precisely intervene in the disturbance stress field and the process of rock fracture and bulking evolution to achieve surrounding rock control,” Liu explained. These research results have been applied to over 40% of kilometer-deep mines nationwide, supporting the construction of a number of kilometer-deep mines such as Guqiao Mine, Zhangji Mine, and Wangfenggang Mine in the Huainan area, with cumulative application in over 2,000 kilometers of deep roadways, effectively controlling bulking large deformation disasters.

Li Xibing, a professor at Central South University, pointed out that deep mining faces a multi-phase, multi-field coupled environment. The solid, liquid, and gas multi-phase coupling under stress and structural fractures not only individually affects the stability of the surrounding rock but also couples with seepage, thermal, and chemical fields, adding new multi-source instability factors to the already complex rock structure.

“Deep rock masses face a dynamic-static combined stress state of high stress plus blasting or mechanical excavation disturbances. Deep rock engineering exhibits typical failure modes such as rock bursts, spalling, and zonal disintegration. Conventional rock mechanics theories and experimental methods cannot explain these unconventional failure mechanisms in deep rock. There is a need for in-depth understanding of the fracture characteristics and precursor patterns of deep rock to achieve accurate early prediction of rock mass failure,” Li said.

“Efficient and safe deep earth development requires deep integration of rock mass intelligent identification, intelligent disaster early warning and control, and innovative support technologies,” Li suggested. He recommended conducting research on unmanned deep mining production processes and systems, achieving intelligent control of hard rock mining, solving the problem of delayed information transmission in underground stopes, and finding suitable intelligent mining methods.

Zhang Nong, a professor at Xuzhou University of Technology, pointed out that existing engineering conditions and stress environments make roadway deformation and damage inevitable, requiring diverse technical support for deep mine roadway excavation and support.

Zhang noted that ground pressure in deep mine roadways exhibits characteristics of larger rock mass involvement, faster deformation and damage rates, and longer adjustment times. The shallow surrounding rock bolted structure shows structural sliding rheology and overall squeezing, displaying loose coupled deformation characteristics. The surrounding rock surface shows fluctuating cumulative deformation, while internally, it exhibits zonal coupled failure.

“Conventional control ideas and support methods have significantly reduced adaptability, requiring new types of support—innovations in support technology and materials,” Zhang stated. To address this, Zhang and his team developed multi-layer continuous reinforcement technology based on a thick-layer anchoring structure, and developed large-size extendable bolts and flexible rod bolts, improving support strength.

At Wangwa No. 3 Mine of Wangwa Coal Industry, part of Chinalco Ningxia Energy Group, a large-section rock roadway in argillaceous soft rock required multiple repairs and continued to undergo large deformation. Zhang and his team applied a new solution of thick-layer anchoring combined with three-level continuous support, reducing the depth of roof separation development to less than 3 meters and decreasing surrounding rock deformation by 46%.

Promising Prospects for Green and Low-Carbon Mining

“The coal industry faces three major challenges: mining-induced damage, solid waste disposal, and carbon emissions,” said Wang Shuangming, Academician of the Chinese Academy of Engineering. Mining-induced damage leads to resource loss, geological damage, and environmental harm. Coal-based solid waste stockpiles exceed 13 billion tons and are growing at a rate of over 1.5 billion tons per year. The scale of stockpile resource utilization is small, and the level of incremental resource utilization is low. Carbon dioxide emissions are substantial, and the task of emission reduction is heavy.

Wang suggested addressing these three challenges—mining-induced damage, solid waste disposal, and carbon emissions—through three approaches: reduced-impact coal mining, functional utilization of waste, and carbon sequestration and disposal.

“By utilizing underground spaces created by coal mining, tapping into the resource attributes of coal-based solid waste, and developing the chemical activity of carbon dioxide, we can construct a technology system for reducing damage, reducing pollution, and lowering carbon emissions, achieving coordinated development of coal mining, solid waste disposal, and carbon dioxide sequestration,” Wang said.

In terms of reduced-impact mining, technologies such as localized backfilling behind the support in fully mechanized mining faces and the integrated “excavation, backfilling, and retention” of inter-face coal pillars can be applied. For functional utilization of waste, technologies for preparing all-solid-waste backfill materials and salt-solidifying aggregates can be used. For carbon sequestration and disposal, approaches include constructing goaf spaces for carbon dioxide storage, innovating storage technologies using fractured zones, researching geological conditions for borehole storage, conducting experiments on in-situ pyrolysis of tar-rich coal, and testing underground coal gasification technologies in deep seams.

Li Quansheng, a professor-level senior engineer at China Energy Group, noted that in recent years, ecological mining of coal has faced some challenges. Conceptually, there is a lack of understanding of how to minimize disturbance and damage to the surface ecology from the source of mining, manifesting as a focus on vegetation restoration rather than ecological environment restoration. There is also a lack of theoretical support regarding the mechanisms of ecological damage transmission from coal mining and damage-reducing mining based on accurate monitoring and control of strata movement. Technologically, there is insufficient coordination among multi-source monitoring methods in the “space, air, ground, and underground” domains, a lack of ecological restoration and mining damage control technologies based on spatiotemporal intelligent decision-making, and high costs for ecological restoration.

“There is an urgent need to solve the problem of coordinated development between coal mining and ecological environmental protection through technological innovation,” Li said.

Li and his team proposed a concept of ecological protection-oriented mining based on the combination of mining damage transmission control and systematic protection and restoration of ecological elements. They established a technical system for damage-reducing underground coal mining, conducted simulations and monitoring of damage from underground mining, developed technologies for constructing modular wedge-shaped dams for safe and efficient water storage in underground coal reservoirs, and created a multi-element, multi-scale “space, air, ground, and underground” ecological damage monitoring system for coal mining. They also developed an ecological protection-oriented mining concept for surface coal mines involving “damage-reducing mining, three-dimensional protection, and systematic restoration.” These technologies have been applied in 21 large surface coal mines and 55 underground coal mines in ecologically fragile areas.

Wu Aixiang, Academician of the Chinese Academy of Engineering, pointed out that paste backfilling is an important technology for safe and green mining, helping to prevent goaf and tailings pond disasters at the source, ensuring waste rock does not leave the mine, tailings do not enter ponds, and the surface does not subside.

Wu introduced that typical paste backfilling processes in China’s coal mines include separation layer grouting paste backfilling, paste backfilling behind the support in fully mechanized mining faces, and strip mining paste backfilling (continuous mining and continuous backfilling). In recent years, untimely backfilling (imbalance between mining and backfilling) or backfilling not reaching the roof has caused several mine accidents, and concentration is the most important factor affecting the fluidity and strength of paste backfill.

The Jiangzhuang Coal Mine project for paste backfilling behind the support is the first mine under Shandong Energy Group to achieve a monthly output of 50,000 tons from a single backfilling working face. The project, with an annual design capacity of 600,000 tons, uses an integrated modular crushing system, an intelligent mine backfilling system, and split-type backfilling isolation supports. After optimization, the channel behind the support was extended to 2.4 meters, allowing the rear isolation device to remain stationary during backfilling grouting while the front face could cut coal in three passes, achieving parallel operations of mining, backfilling, and support, as well as parallel operations of isolation, support, and inspection.

“Unmanned backfilling is the development trend, and creating robot clusters and building remote operation and maintenance platforms are the core elements of unmanned backfilling development,” Wu pointed out.

Wang Yunmin, Academician of the Chinese Academy of Engineering, suggested combining big data and artificial intelligence with resource exploration technology, integrating multi-source data such as geology and geophysics, and constructing ore body prediction models through machine learning to improve exploration success rates.

“Mining and ecological protection should not be opposed to each other. We should follow the principle of protecting in the process of development and developing in the process of protection, achieving coordination between green, low-carbon practices and resource development and utilization,” Wang said.

(Source: China Coal News)