Hardground refers to a distinct, hardened stratum of rock, typically cemented carbonate, that forms on the seafloor during periods of slow sedimentation. In mining, it denotes any exceptionally tough layer of non-coal rock that interrupts softer coal seams or overburden. Hitting hardground often requires switching from continuous miners to drilling and blasting.
Heard on the job
The continuous miner is struggling; looks like we hit a patch of hardground right above the seam.