# Experimental Study on the Efficacy of Water Infusion for Underground Mining of a Coal Seam
## 1 Introduction  
Underground mining is a risky industry due to potential failure or collapse near underground mining coalfaces, which can lead to common accidents in the mine, such as an interruption of mining or, more seriously, human loss [1]. To date, there have been many approaches used to prevent these accidents and the water infusion method is one of them. The water infusion method is the technique where water (i.e., with a certain pressure) is injected into the coal seam ahead of the working face, with or without surfactant. After being injected, water infuses into the seam through fractures, cracks, and cleats, and spreads out radially, far away from the holes [2]. The possibility of using the water infusion method as an effective means of longwall face failure reduction (i.e., reduction of lateral movement of coalfaces for underground coal seams) or dust control has been widely studied in the underground coal mining industry for more than 100 years. Underground mining is a risky industry, with many environmental issues involving dust around coalfaces. Studies on the water infusion method for dust control started early (around the 1970s). As the concept of this method, it requires a certain amount of water under pressure to be injected into coal seams through boreholes to increase the moisture inside the coal seams. In parallel, the dust generated from exploitation is significantly reduced. The conceptual mechanism of this method was reported in detail in the study by [PERSON] [3]. The raw coal dust could be pre-wetted before the coal was crushed. Therefore, the dust source wasconsiderably diminished due to the fact that a weakened dust floating ability is expected after the water is injected and transported along with the fracture systems of the coal seam. In addition, the injected water could be infiltrated into tiny pores of the coal seam. This process could help the whole body of coal become fully saturated and eventually reduce the huge amount of dust released during the crushing process by a longwall shear [2]. As early as the 1970s, [PERSON], [PERSON] [4] reported deals with the water infusion of coalbeds. As found in their study, the respirable dust levels were reduced by about 50-75% on a longwall section after using water infusion. [PERSON], [PERSON] [5] kept studying the effects of water infusion, considering both aspects of cost effectiveness and dust control. An actual coal seam was selected for the field test of their investigation. They found that water infusion is an effective and economical method for reducing the generation of respirable dust on longwalls. The water infusion increased the moisture content of the coalbed and ventilation velocities in excess of 2.54 m/s then reduced dust levels further by dilution and prevented generated dust from boiling back. [PERSON] [6] continued the previous works by [PERSON], [PERSON] [5] by conducting verification in three other case studies. Similar findings were observed in their study for both aspects of the environment and cost-effectiveness. More recently, water infusion techniques have been considered due to their advantages of a low cost and high efficacy. Recent studies have broadly focused on both experimental and numerical approaches [3; 7; 8; 9; 10]. The literature reviewed above clearly indicates the effectiveness of using water infusion techniques for dust control (i.e., environmental impacts). However, research on the utilization of these methods for effective longwall face failure reduction (i.e., reduction of the lateral movement of coalfaces, thus enhancing the stability and mining speed of a coal seam) has not yet been closely evaluated. It should be noted that after the water is injected into coal seams, stress ahead of working coalfaces is re-distributed with the slow relaxation of stress (pressure relief) [11]. In addition, the plasticity of the coal body can also be increased and the brittleness can be decreased with the presence of injected water [3].