# Optimization and Application of Drilling Parameters Based on Gas-Solid Coupling Simulation
## 5 Engineering Practice
### Analysis of Pumping Effects and Technological Advantages  
#### 5.2.1 Analysis of Extraction Effects  
For working face 15101, the mineable length is approximately 270 m, with a daily advance rate of 3.4 m. The directional high-level long borehole coverage section was fully extracted within 80 days of mining activity. Consequently, an 80-day observation period was conducted on the gas extraction performance of the directional boreholes, during which key parameters including pure gas extraction volume, mixed gas volume, gas concentration at the upper corner, and gas concentration in the return airflow were systematically recorded. Figure 10 illustrates the variation curves of mixed gas volume (pure gas volume) in the directional high-level long borehole extraction section, while Figure 11 presents the gas concentration variation curves at the upper corner (return airflow). According to the analysis of Figures 10 and 11, the mixed volume of the directional high-level long boreholes ranges from 16.50 m\({}^{3}\)/min to 24.21 m\({}^{3}\)/min, with an average mixed volume of 21.16 m\({}^{3}\)/min; the pure volume ranges from 0.93 m\({}^{3}\)/min to 11.14 m\({}^{3}\)/min, with an average pure volume of 8.23 m\({}^{3}\)/min; the gas concentration in the upper corner ranges from 0.14% to 0.25%, and that in the return airflow ranges from 0.03% to 0.10%. The gas concentration in the upper corner ranges from 0.14% to 0.25%, and the gas concentration in the return airflow ranges from 0.03% to 0.10%. The mixed volume and pure volume of gas extraction from the directional high-level long drill holes will change with the advancement of the working face. At the early stage of work face mining, the coal seam and overlying rock layer are less affected by mining, and due to the small advancement distance of the work face, the fissure development of the overlying rock layer is incomplete, the tiny fissures formed between the collapse zone and the fissure zone are not effectively guided, and the unpressurized gas affected by the mining is unable to be extracted in the fissure zone under the negative pressure. Due to the air leakage in the mining area, the gas accumulates in the upper corner to form a vortex, which is not easy to be extracted; therefore, in the 1-10 d observation stage, the pure and mixed amount of gas extracted is small, and the concentration of gas in the upper corner rises. As the working face advances continuously, the area of the overhanging airspace area increases continuously, and when the self-weight of the rock layer overlying the airspace area exceeds its strength limit, the roof plate breaks and collapses under the initial pressure, the fissures in the rock layer overlying the airspace area are fully developed, and the number of fissures increases and conduction occurs so that the pure quantity and mixed quantity of the gas extracted increases continuously. After 14 days of mining, with the periodic collapse of the overlying rock layer, the pure volume and mixed volume of gas extraction showed cyclic changes as the working face advanced. Observation results show that, during the observation period, after the initial collapse of the roof slab, the extraction and mixing volume was stabilized at about 21 m\({}^{3}\)/min. During the period of 20 to 34 days, due to the hardness of the roof layer in this section and the increase in the cyclic pressure step, the roof slab failed to collapse in time, which resulted in the lower extraction and mixing volume, but at this stage, the gas outflow from the K\({}_{2}\) and K\({}_{3}\) limestone above the face was larger; therefore the change in the pure extracting volume was smaller. During the period of 34 days to 70 days, the top slab collapsed in time through manual intervention to force the roof release, and the extraction mixed volume increased significantly.