(Q) 4. Mine Design
Room and pillar panel layouts have the following features in 2 North Mine (#1 Seam) as shown in Figure Q6:
- In the mains, development rooms are designed 3m high and 6m wide leaving the pillars 35m wide centre to centre in both 2 North and 4 South mines.
- Panels are developed towards the dip of the seam.
- Panel entries are separated by coal pillars, 22m wide centre to centre and crosscuts are driven along the strike at an interval of 45m.
- The barrier pillar between adjacent pillars is 30m wide.
- Based on the mine map (Figure Q6), the #7 panel is 247.5m wide and 787.5m long. The panels #8 to #12 have varying widths from 135m to 157m. The lengths of these two panels vary from 517.5m to 810m towards the dip of the seam.
- The height of the entries is 2.6 ~ 3m and the designed width is 6m.
There is an open pit on the surface near 2 North Mine. Access drifts to the 2 North Mine are developed from the bottom of the pit. They have the following features (Figure Q6):
- Three inclines are driven following the seam from the bottom of the abandoned pit towards East to access the #1 Seam.
- Two of these entries are for intake air and the third one is for return air.
- These entries are 2.6 ~ 3m high and 6m wide.
Production face design may be described as follows:
- Prior to #6 panel, pillars were wider. Splitting of pillars into stooks was practiced during depillaring.
- The rooms are designed 3m high and 6m wide.
- At present, the pillars in a depillaring panel are smaller and no splitting is required. The pillars are 22m from centre to centre along strike. Crosscuts are driven at 45m interval.
- The depillaring cut sequence follows a Christmas tree pattern leaving the stump pillars at the inby end (Figure Q7).
- The final block within the pillar under depillaring is left unmined in the gob.
- If the roof is sound, full working height extraction is practiced. In case of troublesome roof, the stump pillars are left bigger and the width of fender is reduced.
- In 4 South Mine at the #3 Seam, yield pillars are left leading to partial extraction (Figure Q5).
The entry and crosscut meet at a right angle. Figure Q6 shows that all roadways are 6m wide (unless there is a local problem due to fault). The maximum roof span at the intersection is its diagonal, which is 8.5m approximately and could be wider at completion.
An extended cut is considered to be any cut done by the continuous miner greater than 6m (20 feet) from the last full row of roof bolts. Mostly, the extended cut is 11.55m (35 feet) maximum due to visibility limitation. Extended cuts are used under competent roof conditions.
When geological discontinuities are present, the cutting head is used to scale down immediate roof near the discontinuities. The "two cut" sequence of cutting is undertaken to expedite the simultaneous roof bolting operation (Figure Q8).