Figure 7

The cloud map of the gas concentration distribution of goaf when different diameters of the pipe are used. Figure 7 illustrates the cloud map of the gas concentration distribution under the different diameters of the pipe. When the diameter of the buried pipe reaches 100 mm, the gas concentration in the upper corner does not change significantly, which is still maintained at about 4.01%. When the diameter of the buried pipe reaches 400 mm, the gas concentration decreases obviously. The amount of gas flowing into the upper corner is effectively controlled, reaching 0.37%. At this time, the gas concentration in the deeper goaf would be still high, reaching 12.26%. Further measures need to be taken.