After Flood, Boulder County Chooses Gravity Walls for Emergency Repairs

The Challenge

In September 2013, floods ripped through Boulder County in Colorado, massively damaging the roads-leaving many of them in very dangerous conditions for travelers heading into the mountains.

The stream bank parallel to Lee Hill Road had seriously eroded and was threatening the stability of the roadway. Heavy trucks were continuing to use the damaged road to deliver materials to other flood-damaged sites, and with the spring quickly approaching, the City of Boulder needed a fast and permanent solution to fix the roads before the next heavy rain season.

Civil engineer with Loris & Associates, Inc., Dan Beltzer, PE, said that the biggest challenge was that they needed this wall built very quickly.

“We had to get in and build a retaining wall that beat the spring runoff conditions. We were working against the clock on this, and we needed a wall solution that we could come in and build as quickly as possible,” said Beltzer.

After Flood, Boulder County Chooses Gravity Walls for Emergency Repairs
September 2013 floods in Northern Colorado eroded this stream bank and threatened the stability of the road above.

The Solution

According to Beltzer, the common solution for road repair after a flood is to quickly put an emergency fix in place, then work on designs for a better looking, permanent repair later. Boulder County chose a different route for this repair.

“On this project, Boulder County was interested in doing one repair, at one time, and then be done with it. The Redi-Rock solution fit very well for that, and we designed this gravity wall solution as a one-time fix that fits both the emergency and permanent repairs.”

The gravity system consists of one-ton blocks that rely on their mass to retain the earth. These blocks install quickly and easily – which was a major benefit for this emergency repair project.

Beltzer said the Redi-Rock gravity system was ideal for this project because it fit the geometry of the bank that was created by scour from the flood. “The Redi-Rock gravity wall solution fit very well with leaving that slope in place and building a segmental wall as quickly as possible outboard of that slope, and then flow filling in the remaining void area,” said Beltzer.

The Redi-Rock Ledgestone texture was, aesthetically, the perfect solution for this project, as it fit in with Boulder County’s desire to stay as true to the natural surroundings as possible. “Boulder County is sensitive to wanting to use wall solutions that are complementary to the natural area and the Redi-Rock stones with this particular wall facing fit the bill,” said Beltzer.

Local Redi-Rock manufacturer Signature Stone created the color for the walls by matching rock outcroppings to make the look consistent with the natural environment.

Boulder County Flood Wall
Using Redi-Rock gravity blocks allowed the installers to build the wall in front of the slope, then flow fill in behind the wall once completed.

The Outcome

This gravity wall consists of 60-inch (1520 millimeters) and 28-inch (710 millimeters) blocks in the Ledgestone texture. The wall reaches heights of about 12 feet (3.7 meters) and is load bearing due to the adjacent road.

“Due to the gravity wall application and the proximity to the adjacent road, Redi-Rock ended up being a great fit,” said Seth Clark of Signature Stone.

Boulder County Flood
Ledgestone blocks were chosen to complement the natural surroundings, with the color being matched to natural stone outcroppings in the area.

Project: Lee Hill Road Repair #171
Owner: Boulder County
Block Manufacturer: Signature Stone
Engineer: Loris & Associates, Inc.
Installer: Yenter Companies, Inc.
Location: Boulder, Colorado
Year Built: 2014

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