Cemented coal gangue paste backfill (CCGPB) containing coal gangue and fly ash is a backfilling technique newly developed in coal mines in China that allows environmentally hazardous products, such as gangue and fly ash, to be reused in underground stopes. CCGPB materials provide efficient ground support for the caving of strata and reduce surface subsidence. In this paper, field monitoring of CCGPB properties was conducted in an underground coal mine, which mainly included the measurement of the longwall face temperature, humidity, CCGPB internal hydration temperature, stress conditions inside the backfills, and displacement. First, the components of the backfills, paste technique, slurry generation procedures, coalfield geology, and mining conditions were introduced. Then, a monitoring system was designed in the field. An online monitoring system was installed. The results of the field monitoring showed that the curing temperature significantly varied, i.e., from 26°C near the main gate to 37°C near the tailgate. The curing humidity had the same trends, increasing from 60% relative humidity (RH) near the main gate to 81% RH near the tailgate. The internal hydration process of the paste was divided into four stages, i.e., the rapid hydration stage, slower hydration stage, rapid decline hydration stage, and relatively stable stage. The highest hydration temperature was 50°C, which was measured on the second day after the backfill process. The temperature approached stability at 41°C. The evolution of the roof stress applied on the CCGPB was divided into four stages: the development stage, regulation stage, rapid growth stage, and relatively stable stage. The maximum roof loading was 12 MPa in the middle of the longwall face. The deformation of the backfill experienced four stages, i.e., the rapid deformation stage, slow deformation stage, relatively stable stage, and long‐term stable stage. The maximum deformation was 104.3 mm, appearing in the middle of the face. In addition, the compression ratio of the backfill was approximately 4%. The results of this study showed that the working conditions of backfills in the field were different from those in the laboratory. This paper provides guidance for the design of the CCGPB technique and the predictions of surface subsidence induced by the production process of underground mining.

As resource extraction moves deeper underground, backfill mining has received a lot of attention from the industry as a very promising mining method that can provide a safe workplace for workers. However, the safe and efficient transport of fill slurry through pipelines still needs more exploration, especially in the bend section. In order to investigate the flow characteristics and velocity evolution of the slurry in the bend section of the pipe, a three-dimensional (3D) pipe model was developed using the computational fluid dynamics software Fluent, and nine sets of two-factor, three-level simulations were performed. Furthermore, a single-factor analysis was presented to investigate the effects of the two main influencing factors on the shifting of the maximum velocity of the slurry towards the distal side in the bend section, respectively. Then, the response surface analysis method was applied to the two-factor analysis of the maximum velocity shift and the weights of the two influencing factors were specified.

The development of underground engineering caused a large area of waterlogged area, resulting in damage to farmland and inability to cultivate. An innovative three-dimensional agricultural management strategy was proposed in this study to enhance land management in the affected regions. Three-dimensional models are based on the root characteristics of different crops, and these models are often used to guide planting in the waterlogged area. This strategy combined deep digging and shallow padding techniques, integrating soil management and paddy field coordination to advance modern agriculture. Changes in the area of waterlogging were estimated for various diving levels using field measurements and simulation analysis. The results of the numerical simulation for the area of waterlogging were used to assess the viability of the three-dimensional agricultural model, which included detailed dynamic soil volume changes and groundwater level variations. Furthermore, various crop combinations were examined to determine their rationality within this multilayered agricultural system. The results indicated that the most cost-effective and practical approach involved planting corn in the upper layer, planting lotus roots in the middle layer, and cultivating loaches in the lower layer. This multitiered strategy significantly accelerated the restoration of waterlogged area, offering a more sustainable approach for agricultural practices in challenging environments. The research results are also of great significance for the prevention and control of surface waterlogged area in underground engineering in reclaimed land zones.

Because of various patterns of deep-water inrush and complicated mechanism, accurate prediction of mine water inflow is always a difficult problem for coal mine geologists. In this paper, the water inrush channel is divided into four basic water diversion structures: aquifer, rock fracture zone, fracture zone and goaf. The fluid flow characteristics in each water conducting structure were investigated by laboratory test and the multi-structure and multi-system coupling flow analysis model of different water conducting structures are established to describe the whole process of water inrush. Based on the research of water inrush flow path, the analysis model of different water inrush space structure was established and applied to the prediction of mine water inrush inflow. The results prove that, (1) the conduction sequence of different water-conducting structures and the changing rule of permeability caused by stress changes before and after the peak have important influences on the characteristics of mine water-gushing. Influenced by the difference of geological structure and combined with rock mass RQD and fault conductivity characteristics and other mine exploration data, the prediction of mine water inflow can be realized accurately. Take the water transmitting path in the multi-structure as the research object of water inrush, breaking through the limitation of traditional stratigraphic structure division, the prediction of water inflow and the estimation of potential flooded area was realized and water bursting intensity was predicted. It is of great significance to make a reasonable emergency plan.