The true test of a load-bearing member was not how much weight it could bear before breaking. It was how little it deflected under normal working loads.
In the underground round hall at Milepost Three, four thousand feet beneath the granite cap of Haven-Hold, Giles Croft stood beneath an eighty-foot open ceiling.
Around him, the massive cave junction widened out into a natural dark rock vault four hundred feet across. Here, the main rail tunnel branched into three main alignments: the ore transit heading, the earth-heat power hall, and the newly chosen lower residential quarter.
High above the stone floor, Master Mason Duncan Stone-Splitter and Orson Briggs swung thirty-foot curved iron-hard metal I-beams into place using the overhead frame crane.
Each beam was a slender, elegant rib of shimmering blue-black metal, barely eighteen inches deep, with two-inch flanges that caught the blue glare of the arc lamps.
Keyed into heavy concrete skewbacks blasted directly into the dark rock sidewalls, the iron-hard metal ribs formed a nonstop vaulted canopy over the cave junction. The high-pressure jacks lowered the center keystone pins into their matching sockets. Then, the entire four-hundred-foot vault settled with a single, ringing metal note.
A crowd of three hundred miners and refugee laborers stood below. He watched the slender blue-black arches with tense, upturned faces.
