I-90 Rockfall Design-Build


I-90 Rockfall Design-Build

Awards: 2014 Montana Contractors Association Best Reconstruction of a Rural Project Award and the 2015 Engineering Excellence Award from the American Council of Engineering Companies of Montana, Special Projects Category

In spring of 2013, unusually wet conditions caused several large rockslides along Interstate 90, which provides a vital means of transportation through the Rocky Mountains. The Montana Department of Transportation (MDT) was forced to close the westbound lanes and installed temporary containment rails. However, MDT knew this was a temporary fix and started a slope stabilization project. Sure enough, another slide a mile down the road followed suit a year later. Due to the unpredictability of these slopes, MDT went forward with a design-build project, and turned to Morrison-Maierle and Tetra Tech to come up with a solution to this engineering problem.

The I-90 Rockfall Design-Build Project is noteworthy because this is the first time MDT has used design-build contracting on a geotechnical slope stabilization project in Montana. The engineers also introduced new engineering practices never before used in Montana such as the use of Boulder Busting, and a rockfall attenuator and barrier wall, which have only been used in a few states in the U.S. and in Canada. The engineers and contractors also adopted Unique Drag Line Slope Scaling, a technique that is widely used by miners and the timber industry to clear debris from unstable slopes. This approach proved to be safe and cost-effective. Finally, access barriers also added to the complexity of this project so the team created a special grading and access plan that allowed the contractor to remove unsafe loose material off the top of a slope without trespassing.

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