Photo courtesy of Shannon & Wilson Shannon & Wilson used a mechanically stabilized earth abutment to support a replacement bridge over the Elwha River near Port Angeles.

Shannon & Wilson’s use of a mechanically stabilized earth, or MSE, abutment for the Elwha River Bridge replacement project helped solve the environmental challenges of building on the steep rock slope. The overall project, of which the build back was a major component, replaced a deteriorating, single-lane, 95-year-old bridge in a steep, sensitive environment.

The MSE-reinforced fill slope tied into the steep rock slope. The reinforced slope was also extended beyond the abutment and beneath the bridge to provide support for an abutment foundation for a pedestrian bridge that hangs below the road deck.

The design included benching and wrapping tails of reinforcement above each bench. This feature was a low-cost, easily constructed solution for the contractor.

The reinforced fill slope design required analyses beyond traditional methods and design charts, including the use of fast Lagrangian analysis of continua numerical models. The modeling confirmed an increase in interface strength between the reinforced soil and the rock face.

The final reinforced steep slope includes a vegetative face that blends with the existing topography and plant life. Once overgrown, the final surface will appear to be a naturally steep, earthen slope.