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Montana Demonstration Project: Innovative Culvert Rehabilitation Using Trenchless Technologies
Project Overview and Lessons Learned
Ten of the corrugated steel pipes under U.S. 12 near Helena were in poor structural condition with deteriorated inverts and badly in need of replacement. Sand and debris were accumulating in these culverts, reducing their capacities and requiring constant care by maintenance forces. The poor condition of the culverts prompted MDT to take immediate mitigating measures. MDT had two options to address the problem. Option 1 was to excavate and replace the culverts, which would have required lane closures that interfered with traffic flow. Option 2 was to reline the culverts using trenchless technologies without impeding traffic flow. After exploring the two alternatives and evaluating project and user costs, MDT selected the trenchless technologies to rehabilitate the culverts under U.S. 12. The rehabilitation strategies included the following innovative techniques:
By using trenchless technologies, MDT virtually eliminated the need for lane closures, thereby eliminating traffic congestion due to the work zone and the costs associated with maintenance and protection of traffic control and roadway excavation. The use of the CIPP system and high-density polyethylene pipe (HDPEP) liners substantially improved safety for both the traveling public and workers in the work zone by eliminating the roadway users' exposure to construction activities. The new pipe linings improved the structural integrity of the pipes while maintaining similar hydraulic capacities and improved passage of sediments through the pipes.
Safety, construction congestion, quality, and user satisfaction data were collected before, during, and after construction to demonstrate that trenchless technologies can be used to achieve the HfL performance goals in these areas.
No worker injuries or motorist incidents were reported during construction, which means MDT exceeded the HfL requirements for worker safety. No motorist incidents have been reported since the rehabilitation of the pipes.
Although the quality of the pipes' rehabilitation potentially was improved because the work was done in a controlled environment, the rehabilitation process had no impact on the quality of the pavement surface with respect to noise and smoothness. The existing corrugated culverts trapped sediment at the bottom of the culverts. Both CIPP and HDPEP liners provide a smooth surface, which enhances the flow of the sediments through the culvert to the sediment basins at the outfall and maintains similar hydraulic capacities.
The HfL performance goal criteria for construction congestion were attained, as the project had no impact on traffic flow since the work was done beyond the shoulder edge. Traffic was continuous during culvert rehabilitation, with no impact on trip time or queue length through the construction zone.
The benefits and costs of using the innovative trenchless technologies to rehabilitate the deteriorated culverts were compared with the traditional excavation and replacement approach. Although the cost of using liners was higher for this project, it was the first time MDT used such innovative features in rehabilitating pipes. As a result, the agency did the project on a highway with a lower average daily traffic (ADT) to gain experience. In higher trafficked areas, where lane closures and traffic delays are not permitted, the trenchless technology could totally eliminate interference with traffic flow and be economically feasible by resulting in much lower user costs.
Because of the success of this project, MDT plans to use trenchless technologies more routinely to rehabilitate deteriorated pipes, especially on heavily trafficked highways where lane closure would adversely affect community residents and businesses.
The rehabilitation of the deteriorated culverts using trenchless technologies was a great success. MDT easily met the HfL performance goals on the safety of motorists and workers, construction congestion, quality, and user satisfaction. By using CIPP and HDPEP liners, MDT was able to repair all 10 of the deteriorated culverts effectively in a matter of hours instead of days, without excavation of the roadway, and with no traffic flow interference.
This page last modified on 04/04/11