Steam Tunnel Water Stopping

Steam Tunnel Void Filling for Water Stopping, Roanoke, Virginia


Backfill consolidation adjacent to underground steam tunnel at university caused recurrent sinkholes next to overhead sidewalk. Surface water entered voids along wall of steam tunnels, and then came through cracks in the walls, causing water to stand in the steam tunnel. The block walls of the steam tunnel buckled inwards, which resulted in large horizontal cracks in the tunnel walls, which allowed silt to be eroded into tunnel during precipitation events, requiring water stopping repair.

Multiple infiltration points were identified, along an approximately 80 foot stretch of tunnel. Most of the area had a significant horizontal crack and bowing of the block wall. School maintenance staff were having to backfill surface sinkholes along sidewalk every time it rained.


Due to high pedestrian traffic on sidewalk that is also the tunnel roof, work had to be completed quickly and without any downtime. Additionally, due to the failed walls of the tunnel, the void filling material had to be lightweight to minimize pressure on the wall. A waterproof material was required to help block water flow into the tunnel.


High density polyurethane grouting to fill the voids under the overhead sidewalk adjacent to the failed walls.


Single CJGeo polyurethane crew installed more than 400 pounds of high density, waterproof high density polyurethane to fill voids and seal against water intrusion for this water stopping repair. The work was completed during daytime hours, yet did not disrupt student use of the sidewalk. Volume of installed material was more than 6 cubic yards, which explains why material installed on surface to fill sinkholes kept “disappearing” after rain events.