Demodara Nine Arch Bridge railway masonry: lime-cement mortars and catenary thrust vectors?

The Nine Arch Viaduct at Demodara (Bridge No. 40) is an unreinforced masonry arch bridge constructed strictly of dressed granite blocks, high-fired clay bricks, and hydraulic cement-lime mortar. Because structural steel was unavailable during World War I, engineers designed semi-circular arch barrels (each spanning 30 feet) that operate entirely in compression. When a 120-ton diesel locomotive rounds the 10-degree curve across the viaduct, dead weight and lateral centrifugal braking forces resolve into downward thrust lines that stay within the middle third of the arch ring. These vectors travel down into massive tapered stone piers founded directly on unweathered charnockite bedrock.