Challenge
Creek bank erosion underneath a retail commercial center was starting to expose foundations and risked destabilizing the entire structure. A retaining wall adjacent to a parking lot area had also been severely affected. Action was needed to prevent serious damage or the entire loss of a high value complex.

Action
The eroding bank under the Center required installation of a 350 foot long, by 15 foot high concrete slope protection system. The existing retaining wall needed to be replaced with a new 15 foot high wall installed at the edge of the parking lot. Both structures required vertical and lateral support. Subsurface soils consisted of a mixture of sandy silt, gravel, and weak sandstone. Because of the certainty of collapsing soils, as well as tight access conditions and limited overhead under the building, helical piers and tiebacks were chosen over a traditional pier and drilled tieback solution. After installation of creek protection measures and grading, 180 vertical pier and horizontal tieback helicals were installed. A first layer of shotcrete was then applied which was laterally supported with steel plate and nut assemblies on the tensioned tiebacks. A second layer of shotcrete was then applied to the entire project and was sculpted and colored at the parking lot to resemble native soil and stone. Because the project was located adjacent to a creek, a total of 8 federal, state and local agencies had jurisdiction and required permits, inspections and coordination. The Federated Indians of Graton Rancheria were also involved due to the discovery of human bones during the investigation and design phase. Because the project was on a protected waterway, all work under the Complex had to be completed by Sept. 30th, giving a construction schedule of only 2 months. RWR not only met the schedule, but also completed the job a week early.

Results
Today, the property is sound and fully occupied, and the creek no longer threatens the structure. Recent photos show the creek water crystal clear, while the building sits securely on a solid foundation over the creek banks.

Helical Anchors

July 2, 2019

Fair-Anselm Plaza: Creek Erosion Mitigation Spares Marin Shopping Center

Creek bank erosion underneath a retail commercial center was starting to expose foundations and risked destabilizing the entire structure.

May 13, 2014

Failing foundation and rotting mud sill and rim joist

Our estimator, Trevor, got a call to inspect a foundation problem, and came back with these images, as well as measurements and assessment of the…

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