Project Information
Name of the Nominated Project: 2013 Flood Damage Repair, Crawford Gulch Road Retaining Wall
Accomplishment - 2013 Flood waters undermined approximately 460ft long by 10ft wide by 25ft deep section along the east side of the asphalt roadway cutting into and undermining the roadside embankment compromising the sub base, base and road surface. The scope of work called for the 460 linear feet of damaged area be excavated down to bed rock depth. The single lane roadway that was remaining was shored for traffic to pass during construction of the Mechanically Stabilized Earth (MSE) wall. Then construction of an MSE wall back up to the original road way elevation.
Criteria:
Innovation - During excavation, it was determined that bedrock depth was approximately 4’ to 8’ lower on average than what was anticipated. This presented several issues with constructing the retaining wall per the original plan. The deeper bedrock depth was not able to be identified prior since the temporary shoring had to be installed prior to excavation activities. This resulted in the contractor not being able to excavate further down to have the foundation of the wall bearing on bedrock without having to redesign and possibly reconstruct the temporary shoring. The additional wall height would have required the geogrid reinforcing to be extended further into the embankment potentially making Crawford Gulch Road too narrow to maintain traffic during construction. The only other method to maintain traffic on Crawford Gulch Road while having enough reinforcement for the taller wall would have been to install permanent shoring in lieu of the temporary shoring and designing the connections for the geogrid reinforcement to the permanent shoring. This would have been a timely and costly construction effort. The other option that was identified to address the issue was to construct a micropile cap foundation which would address the global stability concerns while not increasing the wall height and thus deepening the excavations, lengthening the reinforcement behind the wall, or impacting the already installed temporary shoring. It was decided that the micropile cap foundation was the most cost-effective alternative over placing the wall on bedrock.
Achievement – The project achieved all its goals including the improvement of the transportation infrastructure.
Transferable – The micro-pile foundation designed for this MSE wall would greatly help any other communities that encounter the above type of bedrock problems.
Cooperation - This decision was a collaborative effort between the County, the Engineers, and the Contractor. Without the teaming effort and quick responses of all parties, the project would not have been completed in time to re-open the road to traffic before winter.
Three Sentence Nomination Summary
Jefferson County is nominating the Crawford Gulch FEMA Flood Recovery project which consisted of constructing four different retaining wall systems along a two-lane asphalt roadway in mountainous conditions. The entire team (Owner, Engineer, and Contractor) worked together to maintain safe passage for traffic throughout the project while encountering challenging site conditions including re-designing an innovative foundation system for the largest retaining wall on the project (and in the entire County). By using a project website, on-going communication and public meetings, the County could keep affected stakeholders (including residents and emergency responders) up to date on expected delays and milestones and allow them to adequately plan their trips.
