# The Preparation of Active Support-Based Sealing Material and Sealing Effect Analysis
## 1 Introduction  
The mining of coal resources in deep mines is likely to face the predicament of \"five highs and two disturbances\". In particular, the gas outburst caused by coal seams of high gas and low permeability seriously restricts the safe production and sustainable development of mines [1, 2]. The fundamental way to effectively solve the problem of gas outburst is gas pre-pumping, and the key method that determines the effect of gas pre-pumping is the quality of sealing [3, 4, 5, 6, 7]. According to the statistics, the pre-pumping concentration of gas in about 65% of high-gas mines is lower than 30%, which can be attributed to the poor sealing quality of boreholes for gas drainage [8]. Currently, the commonly used sealing materials in China include polyurethane, cement-based material and high-water material [9, 10, 11, 12]. As a polymer foaming material, polyurethane has the advantages of being lightweight, having a large expansion rate andbeing simple to operate. However, due to its poor permeability, it can not penetrate into the micro-fissures and fractures around the boreholes; due to its low strength and large compression deformation, it cannot provide support for the boreholes, thus causing poor borehole stability and gas leakage channels around the boreholes [13]. In addition, the foam rate of polyurethane is too high, frequently resulting in an insufficient sealing depth. In this case, the borehole and the roadway plastic zone would be connected to a gas leakage zone [14; 15]. High-water material is widely used in goaf filling because of its simple filling process and low filling cost. In recent years, it has also been used in downhole sealing [16]. With the increase in the water-cement ratio, the grouting property and permeability of the high-water-content expansion material increased, while the strength and timeliness decreased [17]. However, the weathering characteristics of high-water materials lead to the weakening of the sealing effect with the extension of the extraction time [18]. Cement-based material is cheap and can be adjusted by adding additives; thus, it is widely used in borehole sealing. Scholars both at home and abroad have conducted a lot of research into the performance of cement-based sealing material [19; 20; 21; 22]. As cement-based material is injected into the borehole, the surrounding rock is blocked and reinforced, thus greatly improving the gas-pumping effect [23; 24]. However, the cement-based material can hardly provide active support for the borehole, which leads to its failure to reduce or inhibit the development of fractures during the initial sealing of the borehole. In the later stage of pumping, the cement-based material is prone to the phenomenon of water loss shrinkage, which reduces the gas-pumping effect [25]. The most common sealing materials used in mining are mainly made of expanded cement, although the traditionally used expanded cement has poor fluidity, low strength and certain shrinkage after setting, which creates slurry in the sealing material in the early stage of drilling and means that sealing cannot be fully injected into the cracks of coal and rock mass. Moreover, the shrinkage of the expanded cement after setting provides a new air leakage channel, which leads to only a small improvement in the stability of drilling. The gas leakage channel also reduces the efficiency of gas extraction [26]. In view of the shortages of different types of sealing materials, scholars have conducted a lot of research into the sealing materials used in extraction drilling in recent years. [PERSON] [27] and [PERSON] [28] et al. studied the effect of the molecular structure of a high-efficiency water-reducing agent on the fluidity of a cement slurry sealing material, and the study showed that a smaller molecular structure was helpful in causing the dispersion of cement particles and improved the fluidity of the fluid slurry sealing material.