# Delayed-Expansion Capsule Sealing Material for Coal Mine Overburden Isolated Grouting
## 5 Sealing Effectiveness  
### Experimental Design  
To measure the sealing condition of the sealing material in the fracture, a fracture grouting sealing test model was designed to simulate the grouting sealing process under different fracture opening conditions and evaluate the sealing effect of the sealing material. The main body of the model system had a length of 1020 mm and width of 240 mm and consisted of two rectangular acrylic boards with equal size and thickness of 15 mm. Grooves were ground into the top surface of the lower plate using a sanding machine, creating a rough texture to simulate the irregular nature of stratum slurry cracks. These grooves were hollowed to varying depths to represent fractures with different degrees of openness. In the bottom of the three identical lower templates, 2, 4, and 6 mm slots were hollowed out, sealing tape was glued to the edge of the upper plate, and holes were created at equal intervals between the edges of the upper and lower plates. Additionally, bolts were used to connect the upper and lower rectangular acrylic plates to seal the sealing tape, ensuring that the fracture simulation was airtight. Grouting holes were reserved at the upper boundary of the upper plate to simulate grouting injection. The internal width of the three different apertures of the fracture was 200 mm, and the length of all fractures was 1000 mm (Figure 12). The main body of the experimental device was a three-sided seal, with a slurry outlet on the left side as a channel for the slurry running through the fracture. A measuring cup for recovering the leaking slurry was placed at the outlet on the left side, and an electronic scale was placed under the measuring cup to measure the mass of the slurry leakage continuously during the grouting process. The leakage rate, K, is used to describe fracture sealing, and is defined as follows:  
\[K=M_{l}/T_{l} \tag{2}\]  
where \(M_{l}\) is the mass of slurry that was lost (g), and \(T_{l}\) is the time taken to lose the mass of \(M_{l}\) (min). Figure 11: Variation curves of fluidity under different particle sizes and film cover ratios: (**a**) 20-mesh particle size, (**b**) 40-mesh particle size, (**c**) 60-mesh particle size. Grout-filled fracture sealing experiments were carried out using the experimental setup shown in Figure 12. The SAP sealing materials used in the experiment had particle sizes of 20 mesh, 40 mesh, and 60 mesh, with film cover ratios of 20%, 30%, and 50%, respectively. To measure the delayed expansion sealing effect of the sealing material, before using the sealing material for leakage plugging, pure water should be used to carry out comparative experiments to ensure that the sealing material used in the experiments fully expands as it flows to the exit in the experimental setup. In the experimental process, the grouting pump was used with a flow rate of 200 mL/min, and the experimental fissure aperture was set to 2 mm, 4 mm, and 6 mm; the corresponding volumes of the fracture cavities were 400 cm\({}^{3}\), 800 cm\({}^{3}\), and 1200 cm\({}^{3}\). The theoretical flow time for the slurry to diffuse from the grouting holes to the slurry outlet of the fracture within the fracture cavity was 2 min, 4 min, and 6 min, respectively. The expansion time of the sealing material was obtained from a previous experimental study. Table 1 lists the time and mixing time required for the SAP sealing material with different particle sizes and overlay ratios to reach full expansion when the fracture apertures were 2 mm, 4 mm, and 6 mm.