In September of 2013, rainfall in excess of 20-inches over five days caused severe and widespread flooding in Colorado’s Front Range. As a major stream in one of the hardest-hit areas, Left Hand Creek saw 500-year flood volumes resulting in significant damage to many of the bridges and culverts along its reach. The double-cell box culvert at US Route 36 was one of the structures most severely damaged. Due to significant scour underneath the box culvert and erosion of the roadway embankment caused by water overtopping the road, the Colorado Department of Transportation (CDOT) closed US Route 36 at this location citing concerns that portions of the roadway could collapse. American West Construction, LLC (AWC) was then called to assist in performing emergency repairs.
Upon being contacted, AWC quickly mobilized to the site and immediately began work to accomplish the first objective of opening the highway to at least one lane of traffic. AWC accomplished this within 48 hours of mobilization by clearing the road of debris and installing temporary traffic signals at each end of the affected area. While one half of the roadway was still compromised from the flood and at risk of collapse, traffic was safely passed on the unaffected half of the roadway.
AWC then commenced work to repair the damaged box culvert and stabilize the heavily eroded roadway embankment. This work included installation of a soil nail and shotcrete wall against the exposed embankment on each side of the box culvert. AWC also constructed a water diversion to convey the active creek flows past the work area. Once water flows were controlled, AWC dewatered the work area and placed suitable fill material within the scoured area below the box culvert to support the culvert and restore the natural creek bed.
Additional repair work included clearing and grubbing, solid debris removal, tree trimming, channel grading, replacement and extension of corrugated metal pipe culverts adjacent to the creek, placement of large boulders and riprap within the channel upstream and downstream of the box culvert, guardrail removal and replacement, and roadway striping removal and replacement.
Upon completion of the emergency repair work, the diversion pipe was removed and the creek was allowed to again pass through both cells of the existing box culvert. With the road completely stabilized and no long at risk of collapse, the temporary traffic signals were removed and the traffic was allowed back on the highway in both directions.