This essentially vertical wall supports high E 80 loads (night traffic) and LRT commuter rail traffic during the day. By using reverse batter counterforts a planting space is provided between the wall tiers. Internal wall landscaping is unique to the Stresswall System and softens and aesthetically blends the wall face into the environment while eliminating the possibility of graffiti on the wall surface and associated removal costs.
This ASCE award winning wall is the result of a value engineering proposal submitted to SANDAG (formerly MTDB) by the contractor. The original plan design was a typical MSE wall that required very specific wall fill. All of the wall components are precast/prestressed elements and were made locally. The essentially vertical wall with internal planting offset between the counterfort tiers are possible due to the unique revers batter counterfort configuration. Morrison Knudsen was the engineer for the wall.
Brad Lewis (with KTU&A), the landscape architect, selected indigenous plants that alternatively bloomed continuously so that the wall face always has a variable color pallet. Since emitters are used for irrigation water use is at a minimum.
One of the factors that added VECP was the reduced cost of fill for the counterfort wall compared to the MSE wall. By utilizing construction debris from a landfill substantial savings were realized. In addition, the erection rate for the counterfort wall was substanially faster than would have been the case for an MSE wall.
The MSE wall also required internal cip foundation supports for the catenary poles for rail power lines. Due to the structural capacity of the precast counerforts special counterforts were designed to support both the top tier wall panels and to be utilized as foundation support members for the catenary poles.
This wall, as well as other Stresswalls supplied to SANDAG, are designed for locomotive E 80 traffic. During the day the rails are used by LRT lines whereas at night freight lines utilize the line.
This project is the result of a VECP proposed to the Bureau of Reclamation by the contractor. The wall supports the access road to the Theodore Roosevelt Dam Power Station.
The original design was a typical massive cip wall. Field testing determined that ground anchors would be required to both pre-compress the insitu soil as well as enhance wall stability. Therefore the wall has a unique foundation configuration. By including a cip grade beam with vertically oriented mini piles over which the counterforts were placed provided adequate foundation bearing capacity for the wall. In addition, following placement of the base counterforts, ground anchors (tie backs) where inserted through the cip grade beam that was cast over the tails of the counterforts.
Following the installation of the base tiers and anchors the subsequent upper tier components were placed. Site excavated cut material was used for wall fill.
This 1.5 mile 8′ high wall was constructed in the spring when there are typically no hurricanes or major storms. Although unfortunately that was not the case the wall components were placed quickly and reaches filled between high wave events.
The other bid option was a panel MSE wall system. Due to the fact that the counterfort wall can be designed to use a wide range of wall fill including the “clayey” site material the low bidder selected Stresswall partially due to the fill savings compared to the spec. fill for the MSE wall option
The 8′ high ‘seawall counterforts” were cast at Manco in San Antonio and delivered to the site. The shots show the counterfort elements stored on the beach in front of the wall. By working off of the existing embankment excavators placed the counterforts into slots cut into the existing slope. The excavation costs were therefore substanially less for Stresswall than would have been the case for the MSE option.
The “elevated base seawall” counterfort has a unique configuration which results in the minimum excavation volume as well as providing the counterfort support base at a higher elevation than the bottom of the wall elevation. This element geometry facilitates an efficient component erection even in high tide conditions. Also, since the counterfort base is elevated compared to the bottom of the counterfort face, the resultant earth and surcharge loads passes through the counterfort base so the overturning moment is at a minimum. Due to the elevated base the wall foundation loading approaches the minimum value of gamma times h where h is the wall height.
The Mid-Coast Transit Corridor Transit Project is currently utilizing All the Walls’ Stresswall precast post-tensioned/prestressed counterfort wall system for the Midcoast Corridor Transit Project. The MCTC project extends the light rail from Old Town north to UCSD and La Jolla. It also adds a second heavy rail track through the entire Midcoast corridor.
The rail corridor runs through Rose Creek Canyon with 4 tracks: 2 light and 2 heavy E 80 rail. Due to the additional live tracks, there is a need for many different retaining walls along the alignment. There are both cut and fill wall applications since the track grade is also being raised in places to be above the 100-year flood elevation.
All the Walls originally approached Mid Coast Transit Constructors, the general contractor for the project, starting in 2015 proposing the Stresswall design as an alternative, cost effective option that met or exceeded all of the E 80 and LRT load criteria. MCTC realized the cost effectiveness and time savings available with the system so they successfully value engineered Stresswall for many of the walls.
Walls 508 and 563 were originally designed as CIDH soldier pile walls with two-stage tiebacks. Conventional walls of this type would be very expensive and time consuming to construct, as well as the associated inherent risks involved with drilling in difficult areas.
After months of extensive design review meetings with SANDAG, NCTD, WSP, HDR, TY Linn and other design firms, the Stresswall option was approved for construction. The acceptance of the Stresswall system on this project saved millions of dollars in construction costs that were credited back to SANDAG and MCTC and also saved months on the critical path construction schedule. Construction of these walls has gone very well and all parties are pleased with the design and final product.
Wall 482 ( 4,500 sq. ft.) was built over a weekend with two crews working around the clock while the track was shutdown. This site was excavated and the precast components installed and backfilled in 47 straight hours. The original approved plan design was an MSE wall backfilled with Cell Crete, which would not have been cost effective.
Walls 600 and 624 were both originally designed as MSE walls, however North County Transit District (NCTD) no longer allows MSE walls to be built to support their track embankments, so Stresswall was selected as the most viable alternative. The change to Stresswall eliminated the shoring that would have otherwise been required for MSE walls, resulting in substantial excavation savings while providing with a total precast/prestressed product.
This project used All the Walls’ patented proprietary retaining wall system. It was also awarded PCI’s 2019 Best Non Highway Bridge Project.
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El Cajon Calif.