Based on obtained results one can conclude that the lower value of destratification resistance of rocks forming the goaf with caving, the bigger difference of air pressure flowing through these gobs, and the greater resistances of this flow.
7, 8 and 9 there are presented characteristics of velocity distribution of air stream flowing through gobs forming by rocks with different value of destratification resistance along to measurement lines situated perpendicular to the front of the longwall.
Independently from value of destratification resistance of rocks the greatest values of velocity occur from the inlet side of goaf with caving and from the air outlet from gobs to the operating area of longwall.
In the analyzed cases, at initial segment of goaf with caving velocity of air has the greatest value from the side of air inlet to the gobs and from the outlet side of air from these gobs to operating area of longwall.
As shown in Figure 1, wells #1 and #2 are located in adjacent gobs, which have similar geometrical and geological conditions.
Figure 9 shows that, over 80 days of extraction at well #3, the methane volumetric flow rate decreased significantly from 325 [m.sup.3]/h to 130 [m.sup.3]/h, indicating the near exhaustion of methane in the gob. At this point, well #3 was closed for approximately 200 days to allow the methane from the surrounding gobs to flow into that gob, accumulating until the methane pressure returned to its original level.
It is necessary to extract the methane from abandoned gobs, which can contain considerable methane resources.
Aquifer positions above abandoned gobs were detected and sealed before drilled wells entered the gobs.
Therefore, the rock-overlaid roof structure in different gobs are similar to a certain extent.
6 that if the spacing of close distance coal strata is less than the height of natural arch due to the excavation of lower coal stratum, the roofing of the gobs will penetrate each other when the two coal strata are excavated.
The inclined length of the working faces of the coal strata is relatively large, the arrangement of waste rocks under the natural arch in the gobs is loose and the horizontal force in the waste rocks is small.
It is evident from Figure 6 that the due to the spacing of complete stratum in close distance coal strata, the weight of the natural arch of upper coal stratum, waste rocks in the gobs and the complete rock stratum between the two coal strata is fully sustained by the natural arch of lower coal stratum, but the weight of waste rocks in the gobs of lower coal stratum acts independently on the coal stratum flooring.