Progress in the research and application of coal mining with stowing

The development and achievements of modern coal mining with stowing are discussed in this paper. The necessity of developing coal mining with stowing is briefly summarized and internal damage within the strata and external damage on surface induced by longwall working with caving are discussed. Technological features of coal mining with pneumatic stowing in Germany, and fully mechanised coal mining with solid dense stowing in China, are discussed. In German hard coal mining stowing technologies are for technical, infrastructural and economical reasons not applicable. The discussion includes the stowing material transportation system, the stowing machine, and processes at the face. Progressiveness and application universality of China's fully mechanised coal mining with solid dense stowing are illustrated through practical examples with different conditions. Obviously, the fully mechanised coal mine with solid dense stowing can be improved by automaion systems. This paper discusses further developmental potential of the technology.

Ground pressure and overlying strata structure for a repeated mining face of residual coal after room and pillar mining

To investigate the abnormal ground pressures and roof control problem in fully mechanized repeated mining of residual coal after room and pillar mining, the roof fracture structural model and mechanical model were developed using numerical simulation and theoretical analysis. The roof fracture characteristics of a repeated mining face were revealed and the ground pressure law and roof supporting condi- tions of the repeated mining face were obtained. The results indicate that when the repeated mining face passes the residual pillars, the sudden instability causes fracturing in the main roof above the old goal and forms an extra-large rock block above the mining face. A relatively stable ＂Voussoir beam＂ structure is formed after the advance fracturing of the main roof. When the repeated mining face passes the old goaf, as the large rock block revolves and touches gangue, the rock block will break secondarily under overburden rock loads. An example calculation was performed involving an integrated mine in Shanxi province, results showed that minimum working resistance values of support determined to be reason- able were respectively 11,412 kN and 10,743 kN when repeated mining face passed through residual pillar and goaf. On-site ground pressure monitoring results indicated that the mechanical model and support resistance calculation were reasonable.

The Recent Technological Development of Intelligent Mining in China

In the last five years, China has seen the technological development of intelligent mining and the application of the longwall automation technology developed by the Longwall Automation Steering Committee. This paper summarizes this great achievement, which occurred during the 12th Five-Year Plan （2011-2015）, and which included the development of a set of intelligent equipment for hydraulic-powered supports, information transfers, dynamic decision-making, performance coordination, and the achievement of a high level of reliability despite difficult conditions. Within China, the intelligent system of a set of hydraulic-powered supports was completed, with our own intellectual property rights. An intelligent mining model was developed that permitted unmanned operation and single-person inspection on the work face. With these technologies, the number of miners on the work face can now be significantly reduced. Miners are only required to monitor mining machines on the roadway or at the surface control center, since intelligent mining can be applied to extract middle-thick or thick coal seams. As a result, miners＇ safety has been improved. Finally, this Darter discusses theprospects and challenges of intelligent mining over the next ten years.

Investigating spatial and temporal variations of soil moisture content in an arid mining area using an improved thermal inertia model

Mining operations can usually lead to environmental deteriorations. Underground mining activities could cause an extensive decrease in groundwater level and thus a dramatic variation in soil moisture content（SMC）. In this study, the spatial and temporal variations of SMC from 2001 to 2015 at two spatial scales（i.e., the Shendong coal mining area and the Daliuta Coal Mine） were analyzed using an improved thermal inertia model with a long-term series of Landsat TM/OLI（TM=Thematic Mapper and OLI=Operational Land Imager） data. Our results show that at large spatial scale（the Shendong coal mining area）, underground mining activities had insignificant negative impacts on SMC and that at small spatial scale（the Daliuta Coal Mine）, underground mining activities had significant negative impacts on SMC. Trend analysis of SMC demonstrated that areas with decreasing trend of SMC were mainly distributed in the mined area, indicating that underground mining is a primary cause for the drying trend in the mining region in this arid environment.

Utilisation of transparent synthetic soil surrogates in geotechnical physical models: A review

Coal extraction in Huainan area is basically characterized by one of typical multi-seam mining conditions observed in China, where coal is mined in soft seams characterized by high gas content, high stress, low permeability and difficult geological conditions. The average mining depth in Huainan area is 875 m and continues to increase by 15-25 m annually. The rise in mining depth increases the risk of coal and gas outbursts and makes it more difficult to control outburst risk in Huainan coalmines. This paper reviews the main achievements（e.g. theories, technologies and equipment） in outburst control in Huainan, and tries to analyze some key challenging issues, and to present associated strategies to address these issues.It suggests that the outburst control in Huainan must take a combination approach of both regional and localized control in which the former plays a dominant role. Other outburst prevention principles include（1） non-outburst seams protecting outburst seams,（2） less outburst-prone seams protecting strong outburst-prone seams,（3） stress-releasing mining, and（4） the combination of ground and underground gas drainage（the model is dubbed as ＂walking on two legs＂）. The paper concludes that we should conduct fundamental researches on outburst mechanism, and develop outburst control technologies and equipment to ensure safe and efficient coal mining of deep coal resources in Huainan area.