Stormwater Drain Stabilization in Asheville, North Carolina

Problem

There’s an old saying, “If you have a 14' stormwater drain that has some severe voids behind it, then you’re asking for trouble if you don’t fix it!” That’s not actually an old saying, but it is a fact, and it was a problem that a customer in Asheville, North Carolina was experiencing and needed to remediate before they began to have some real troubles. The 14′ diameter, 1100ft long section of Corrugated Metal Pipe was experiencing erosion under the pipe floor and causing degradation of the invert. Through a bid process, CJGeo—a Virginia-based geotechnical contractor—was selected to remediate the drain using the TerraThane 24-042 geotechnical polyurethane.

Solution

The project design approach was relatively simple; use a two-part polyurethane chemical grout to fill the voids below and along the invert and re-establish contact between the soil and the stormwater drain. The trick: find a polyurethane that can handle highly saturated environments, has enough travel time to ensure the voids are effectively filled, and has enough structural integrity to stabilize and strengthen the culvert for at least 10 years. To meet these needs, CJGeo chose to use the TerraThane 24-042 geotechnical polyurethane. The 24-042 geotechnical polyurethane was a great solution because the system has high structural integrity, optimal spread and cure time, works great in saturated environments, and offers an NSF/ANSI 61 Section 5 safe drinking water certification.

Results

CJGeo, working along the 1100′ of culvert, injected in the 4 and 8 o’clock positions to back grout the bottom 10′ of the culvert. CJGeo had to inject in 12″ of standing water that was caused by a creek, that runs through the culvert, which was temporarily restricted by a cofferdam. The invert was stabilized using a combination of 57-stone, that was placed into the degraded areas of the invert, and the 24-042 polyurethane, that locked the stone in place and made the invert structurally sound and restored flow. CJGeo additionally back-grouted a  33′ x10′ head wall that was being undermined by the creek and causing more water to flow around the pipe rather than through it. Over 17,000lbs of the 24-042 was injected over 5 days, stabilizing the base of the soils, the structural integrity of the invert, and re-establishing soil support back to the storm drain. The life of the drain is estimated to have been extended an additional 10 years before it will need to be relined.