Neighborhood Stormwater Culvert Repair

Stormwater Culvert Repair, Williamsburg, Virginia

Problem:

Very large sinkholes developed in a dense residential neighborhood.  The sinkholes were large enough in some places to allow crawling under driveways and curbs.  In a few locations, the adjacent asphalt pavement was starting to fatigue and collapse.

All of the pipes were man-enterable reinforced concrete pipe (RCP), ranging in size from 40 inches to 60 inches in diameter.  Visual inspection showed that very few of the joints were adequately sealed during installation.  Additionally, the soil in the area was very sandy, so easily eroded through open joints and leaks.

The erosion of the soil into the pipe caused surface water to pipe outside of the culvert.  This washed out the backfill material from below the pipe, which allowed the pipe sections to settle, which caused joints to open up further.  

The impacted area was approximately 2500LF of pipe, and 300VF of structures.

Polyurethane grouting crew repairing RCP culvert pipe.

Polyurethane grouting for culvert repair.

Constraints:

The repair had to address two main problems:  The open joints and leaks in the pipe, and the surface instability caused by deep voids.

Additionally, the community is an active adult community, so traffic loads are relatively uniform throughout the day.  So, the repair could not block access to homes by closing driveways, streets or sidewalks.

Culvert Repair Solution:

Polyurethane grouting was selected as the most economical and effective repair.

For large diameter pipe repair, plural component polyurethane grout is injected through the walls of the pipe from inside the pipe.  The grout expands to fill voids and seal joints in the pipe.  After voids are filled immediately around the pipe, additional polyurethane grout is injected and expands to chase sinkholes and large voids up to the surface.  A surface monitor watches for grout to appear at the top of sinkholes.

A low unit weight plural component polyurethane grout was chosen for the culvert repair.  The material had a 2.5 time safety factor for loading despite being very low density.

Results:

Three polyurethane grouting crews worked to repair the stormwater culvert pipes over a period of a week.  All of the sinkholes were filled with rigid polyurethane.  This restored the integrity of the driveways, sidewalks, curbs & streets.  

Residents were able to continue their normal activities in the area, with no impact.