The railway embankment along Sector Four rested on thirty feet of dense river-bed gravel over a confined artesian silt layer.
It was designed to carry heavy ore trains at fifty miles an hour without ballast settlement.
It wasn’t designed to have two thousand enemy miners excavating an underground cave eighty feet beneath its ties.
Giles Croft walked along the western ditch of the embankment. He carried a brass dipping tape and a clipboard.
Every fifty paces along the gravel berm, a slender two-inch zinc-coated iron pipe stood vertically in the earth, capped with a vented brass screw fitting.
Inside each pipe was a simple open-standpipe pressure tube. A porous baked-clay filter tip at the bottom, linked to a glass standpipe that registered the natural pore-water pressure of the deep soil.
Beside Giles walked Corbin Cross, foreman of the town deep-drilling crews.
Corbin wiped grease from his weathered face, his heavy canvas coat spattered with drilling mud.
