Highland Boulevard Gabion Wall Project (City of Pocatello)
Friday, May 6, 2016
Posted by: Gay Dawn Oyler
In the fall of 2013, the City of Pocatello was hit by two heavy rainstorms within a few week time period. Both storms produced enough precipitation to be classified as 100-year or an occurrence probability of 1%. The intense rainfall wreaked havoc throughout the community and tested the limits of the city’s infrastructure. One of the areas most affected by the storms was along Highland Boulevard, a two lane municipal street providing access to the Hyland Subdivision on the west bench of Pocatello.
The catch basins above Highland Boulevard were unable to collect all of the stormwater, allowing the excess water to run down the street. Due to the high volume and velocity of the runoff and the fact that this happened on a sharp corner in the street, the water overtopped the curb and sidewalk and ran down a very steep slope, causing significant damage to the hillside. The water eroded the support materials from under the sidewalk and guardrail, leaving them suspended in the air. In addition, this erosion threatened the integrity of Highland Boulevard. Later storms continued to erode the area resulting in buckling of the sidewalk and creating additional safety hazards for pedestrians.
Due to the unpredicted nature and size of the storms and the fact that it occurred late in the budget year, there were minimal funds in the budget to repair the damage. In order to reduce the cost of the project and expedite repairs, the Public Works Department decided to utilize City resources to design and construct repairs to the area. Since Highland Boulevard is the only access into the residential neighborhood, closing the street, even temporarily, for repairs was not an option. The staff evaluated various repair methods and ultimately selected a gabion wall system, a series of stacked wire baskets filled with rocks to serve as a retaining wall. The gabion wall system made it possible for repairs to the hillside to be completed without removing the existing street. Other alternatives would have required removal of the street and extensive excavation to provide sufficient anchoring and resistance to vertical and horizontal forces. The weight and geometry of the gabion wall system allows for adequate support with minimal disruption to the surrounding area.
Engineering and surveying for the project were completed by the Engineering Department. The majority of the construction was completed by the Street Department, including excavation and construction of the gabion walls and installation of a new guardrail system. By utilizing City staff and resources, the project cost approximately 65% of what was originally estimated, saving the city approximately $50,000. The collaboration of the City Departments allowed for the timely repairs with minimal disruption to the neighborhood. The outcome of the project was a success.
For more info, contact:
Jeffrey Mansfield, PE
Project Engineer II