Poor roof rock conditions in an underground coal mine.
Just few days back I had a trip to an underground mine in West Virginia. They were mining Pocahontas 3 coal seam. P-3 seam is quite thick in that area and it is a good quality coal too. However they have serious problem with poor roof rock conditions. Many reasons control the stability of roof strata of a coal seam. Drilling and detailed geologic and geotech logging usually performed along with fracture logging to evaluate the stability of both roof and fllor rock within the permit area. Usually multiple drill holes are used for the analysis. Even after that, we can atill have local poor rock conditions due to local faults, folds, change in lithology and so on. Typically in this mine, they had differencial pressure difference betweeh soft shale unit and heavier sandy unit above. The differential compaction produced numerous slikensides in the roof strata making it very unstable roof rock. Along with that, a think rider seam is continueously present slightly above the P-3 coal seam too. Here are some pictures taken in the mine. Feel how it is underground!
Bolts Holding the Roof Rock of a coal Mine.
Under Ground Coal Mine in Operation
Folds at the immediate roof of coal seam. A very rare occurrence. Usually the coal seams are tend to be flat with local low angle folds and faults.
Nice Fossils at the Roof Rock of an Underground Coal Mine
Fossils at the roof an underground coal mine
Ring of coal spar at the immediate roof causing rock fall
Massive Hard sandstone roof – that is what every body wants. Solid and nice.
Sandstone with sharp contact with coal seam – this is what we want! But if you are interpreting coal seam from E-log, you may have some trouble. I will discuss in future in case you need to know.
Slikensided Shaley Roof immediately above a coal seam – This is one example of poor roof. More slikensides you have, poor the roof is with more chances of rockfall.
Slikensided shaley roof supported by roof bolts and wires. – sometime we also cement the roof to avoid rockfall.
Thick, Clean, Soft Pocahontas 3 Coal Seam – check out the nice looking thick Pocahontas 3 coal seam. No pyritic material visible on eye. Great looking coal seam with nice banding.
General look of an Underground Coal Mine – Look how it is at underground!