For those that may not know. The two track single bore tunnels between Dupont Circle and Woodly Park - Zoo has U channels to support the cables along the walls of the tunnel. The bottom of the U channel is bolted to the track slab and the middle and top of the U channel is secured to the irregular tunnel wall surface with an all thread rod welded to the reinforcing fabric embedded in the shotcreate. The cables carry power for the tunnel lighting, fans in the fan shafts, ejector pumps, and wires for the track circuits, vent and fan shaft dampers, smoke detectors, intrusion detectors. . . The trough between the two track is where the cables that terminate in station communication rooms are placed, the cables for the land line phones and emergency trip station boxes.
John in the sand box of Maryland's eastern shore.