Discussion on simultaneous mining of the upper and

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Discussion on the simultaneous mining of the upper and lower layers of close coal seams

1 proposal of the simultaneous mining scheme of the upper and lower layers

according to the actual mining of other mining bureaus across the country, thick coal seams have been mined in layers, and artificial false roofs have been paved between layers for the simultaneous mining of the upper and lower layers; According to the revealed occurrence conditions of coal strata, there is a 0.5 ~ 2.5m roof in the lower layer of 34 # outside the 34 # layer of 8 ~ 9 roads in Didao Coal Mine. It is feasible for the upper and lower layers of 34 # to be mined at the same time

2 scheme design

first, excavate and send the main roadway to the boundary along the 34 # lower layer of erxie 9 Road, and send it up the mountain for mining; When the stone inclusion is less than 0.5m, taking this as the boundary, the full layer is mined at 200m in the inner part of the 34 # layer of Road 9, and the upper and lower layers are mined at the same time at the remaining 500m outside. The mining layout is shown in Figure 1

layout of upper layered roadway: excavate on the slope of 34 # lower layer. After seeing the upper layer of 34 # upper layer, excavate along the upper layer of 34 # upper layer and cut it up. Then, excavate the inclined upper and straight grooves again at a distance of 60m from the upper cut, and connect with the upper cut; During stoping, a sgw-40t/60 scraper conveyor is set up along the chute for transportation, and the enamel chute is directly overlapped on the roadway belt conveyor, which is transported to the coal bunker through the belt conveyor; Inclined upward, along the groove and ahead of the working face

34# the lower layer is directly excavated and cut up, and the mining is carried out 40 ~ 60 m behind the 34# upper layer working face, as shown in Figure 2

3 roof pressure calculation and support design

3.1 upper layered roof pressure calculation

Figure 1 mining layout plan section

Figure 2 upper and lower layered mining step section

(1) roof pressure

where p - roof pressure M can be described as "big" Pa

k - coefficient of fragmentation and expansion of roof rock behind caving

among them, the latter three kinds of equipment are the supporting equipment H - Maximum mining height to cooperate with the impact testing machine to conduct the impact test

ρ—— Average unit weight within the range of roof rock caving height

k1 - dynamic load coefficient, taking 1.3~1.6

k2 - coefficient of suspended roof and slope

k2= (L1 + L2 + L3)


(2) support density (strength)

theoretical support density of working face n1=p/· C=0.32

where p - calculated roof pressure

?—— Rated resistance of single hydraulic prop

c - performance parameters of single hydraulic prop

actual support density of the working face

n2=n/(L1 · E) =1.11

where n - the minimum number of pillars within the maximum roof control distance

l1 - the maximum top control distance specified in the operation procedure

e -- working face column spacing

(3) safety factor (n)

n= N1/n2=3.53>2

3.2 calculation of the roof pressure of the lower layer

the roof pressure of the lower layer is the sum of the weight of limestone and the weight of rock within the range of the upper layer's caving height

(1) roof pressure

p2=p+ p2=16.18~31.48

(2) theoretical support density of working face

(3) actual support density of working face

n2=n/(L1 · E) =2.22

(4) safety factor

n= N1/n2=2.01>2

therefore, it can meet the support requirements to select four rows of single hydraulic pillars to support the roof in the upper layer and four rows of opposite columns to support the roof in the lower layer

4 determination of the stoping step distance of upper and lower layers

according to the stoping of 6 ~ 8 roads 34 # upper layers, the roof periodic weighting step distance is 8 ~ 12M, 30 ~ 40m after mining, and the roof tends to be stable. In order to avoid the impact of the dynamic pressure of the upper layer after mining on the lower layer working face, the lower layer working face is selected to lag the upper layer working face by 40 ~ 60m for stoping

5 several problems existing in roadway excavation and mining

(1) when excavating and transporting the main roadway in layers along the 34 # lower, the anchor cable is used to support the roof. When the stone inclusion is less than 0.3m, the roof cannot be retained. The upper layer roof of the 34 # upper is the main roadway roof. Excavating and transporting along the whole layer may cause the roadway to be as high as about 3.0m, causing certain difficulties for future mining

(2) when the upper layer of 34 # is inclined upward and driven along the channel, the tunneling team must carry out the construction separately in advance, and the return air flow is connected in series with the upper and lower layered working faces

(3) the upper roadway of the working face (the main roadway of 34 # layer on the right 8th Road) is driven along the upper 34 # layer. When mining the lower 34 # layer, it is necessary to dig 1 ~ 2m vertical holes to connect with the upper roadway. It will cause certain difficulties for the transportation of materials, equipment, pedestrians and power supply at the upper exit

(4) after mining in the upper layer, the dynamic pressure after mining may cause cracks in the roof of the lower layer, which will bring difficulties to the mining in the lower layer

(5) the water from the top of the pillar in the upper layer seeps into the rock fissure, causing part of the water to be sprayed during the mining in the lower layer

(6) when mining in lower layers, attention should be paid to the pressure concentration area of the coal wall of the upper layer along the trough, which directly acts on the lower layer roadway

(7) when mining in lower layers, due to the high roof pressure, four rows of opposite columns are used to support the roof, which increases the labor intensity

heat treatment status: after heat treatment (8), because the outside of the 34th floor roadway of the right 8th Road is excavated and transported along the upper 34th floor, therefore, during mining, the technical specification issued by the upper Beijing Municipal Commission of housing and urban rural development is that there is a law that can be based on the layered common working face, and the back roadway of the upper roadway must be reserved for the return air of the lower layered working face

through the above calculation and analysis, the upper and lower layers are mined at the same time, and each plate will recover 100000 ~ 150000 tons of coal resources, avoiding the waste of resources; The utilization rate of the roadway is improved and the connection is relieved

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