Fabric 1 name: Miragrid
Fabric 1 producer: TenCate Geosynthetics
Fabric 1 supplier: TenCate Geosynthetics
Fabric 2 name: Miramesh
Fabric 2 producer: TenCate Geosynthetics
Fabric 2 supplier: TenCate Geosynthetics
Engineer: Kristopher Hauck – Terracon, Portland
Subcontractor: Slayden Construction
Location: Portland, OR
Please describe the project specifications.
In order to meet the project specifications of designing a geogrid reinforced vegetated wirewall with permanent geogrid facing material, A hybrid Vertical Mechanically Stabilized Earth (VMSE) wall using Hilfiker® wire facing baskets and geosynthetic reinforcement was designed. This work consisted of furnishing and constructing Mechanically Stabilized Earth (MSE) retaining walls and Reinforced Soil Slope (RSS) walls. Miramesh® GR is a green mesh facing to provide an instant green face prior to vegetation growth. It is UV coated to provide 75 to 100 year design life for permanent MSE wall face and slope face. It provides surface erosion protection and secondary reinforcement in MSE structures. The erosion protection facilitates establishment of vegetation and provides structural support for the forming of battered and vertical face MSE walls and oversteepened slopes. The secondary reinforcement facilitates compaction and prevents surficial sloughing at the slope face.
What was the purpose of this project? What did the client request?
The Sellwood Bridge is a truss bridge that spans the Willamette River in Portland, OR. It was Portland’s first fixed-span bridge and is the busiest two-lane bridge in Oregon. The bridge’s condition has been deteriorating for years, and in the mid-2000s this led to a decision to replace it. A multi-year project to construct a replacement bridge has been under way since December 2011 and the new bridge is projected to open in January 2016. The client needed to design an extension to the existing public bike path and walking trail that crosses over the bridge. This is a sensitive area where it’s important the public has easy access and be aesthetically pleasing. The extension needed to be built to match the existing path and be able to handle the grade separations. Therefore, they needed a plantable, permanent, vegetated solution.
What is unique or complex about the project?
This job required an Oregon DOT approved wall system so we teamed with Hilfiker to design a solution to meet the project specifications. A Miramesh® (permanent geogrid facing mesh) (PGFM) was installed inside the wire basket to retain the topsoil mix and accept hydroseeding. Wall construction occurred during periods of heavy rainfall but topsoil loss through the PGFM was negligible. This was complex because the site has both vertical walls and terrace walls with irregular shapes. Hilfiker’s black steel facing baskets were used as compaction forms and TenCate’s Miramesh® made up the permanent wall facing. The client, with local engineering expertise from Terracon, relied on TenCate’s extensive UV test results and vegetation support to provide a design using Miramesh® permanant facing geogrid. Vegetation testing shows Miramesh® geosynthetics perform better than biaxial geogrids and geotextiles in providing a suitable platform for plant growth. The uniquely designed aperture construction allows for retention of soil particles, while encouraging vegetation growth. Miramesh® GR is the only permanent geosynthetic facing geogrid in the industry with 75 year life exposed to sunlight.
What were the results of the project?
The client was very happy with this solution. In less than six months from construction, the wall facing had germinated with significant vegetation growth. The wall is continuing to grow and perform as intended. The client hydroseeded the wall face after completion and plants are growing thru the wall and its performing as designed. Since this project, the Engineer, Terracon (Portland) has continued to design other permanent, plantable walls using Miramesh® GR based on previous results. This system continues to be used in Portland area for plantable wall solutions. More recently, it has been used for two big box retail stores and the results are as expected.
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