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Case Study: Weston Corners – Cary NC
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Weston Corners is your typical luxury mixed-use development in many ways. Located in Cary, NC this site did require large retaining walls with one in particular requiring special solutions. The wall in question was originally specified as a Cast-in-Place (CIP) type but faced with bids vastly over budget they needed a different solution. Gib Lyttle, owner of Delta Development was soon brought in and an Allan Block solution was proposed using a special Pilaster Block.
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The engineering firm, TerraTech Engineers, were also involved to overcome the many challenges the site provided. The first being the presence of a gas easement that would interfere with a standard geogrid wall design, with the ultimate solution incorporating a shotcrete wall behind with soil nails to stabilize the soil and avoid the gas easement. This project was also a cut site that would require excavating about 30 ft (9 m) through bedrock to reach the base elevation.
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The experience of the build crew along with the support from all parties involved contributed to making this project a success under difficult conditions that wouldn’t break the budget.
Learn more about this unique AB Retaining Wall project by reading the full case study here or on our website.
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Engineer Talk: Groundwater and its effects on Retaining Walls.
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Water is the number 1 enemy of retaining walls, not just surface water but subsurface as well. As the water table rises, the soil material gets saturated and the bearing capacity of the soil changes for the worse.
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Here are a couple of ways to increase the stability and the bearing capacity of the foundation soils for a retaining wall:
- the poor soil should be removed and replaced with better soil
- the foundation pad should be increased in width and depth
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If the water table is higher up the retaining wall this could cause the saturated soils to apply 1.5 to 2 times the pressure to the wall system. A solution is the use of additional drainage, such as chimney and blanket drains, to capture the water and have it exit the system before it saturates the infill material.
Now if there is water present behind and in front of the retaining wall, this would be classified as a Water Application. To prevent hydrostatic pressure building up within the wall the infill material should be a clean aggregate with no fine particles.
For more information check our Allan Block’s Best Practices document that cover all the above scenarios.
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Tools: Fence Overturning Utilizing MathCAD
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We all know that walls with significant grade changes need some form of fall protection, but there are questions that need to be asked when determining what to use. How deep does the post footing need to go? Or how do you determine the location of that fence/barrier and the impact it could potentially have on a segmental retaining wall? While requirements may vary depending on your local code, Allan Block can assist you running the fence overturning calculations necessary to ensure the stability of your retaining wall.
Using a MathCAD template along with a geogrid reinforced cross section from the AB Walls software and the fence/barrier design parameters a post embedment depth can be determined that will limit the impact on the wall. A more detailed approach to calculate post embedment can be found in Tech Sheet#1113 – Top of Wall Fence Overturning
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Common Applications:
- Pedestrian
- Privacy/Screening
- Security
- Railing/Barrier
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Location, Location, Location! The proximity of that fence to the top of the wall will determine when a fence overturning calculation is needed. When you decide to locate the fence within 3 ft ( 0.9 m) of the top of your wall (including within the cores of the wall blocks) a fence overturning calculation should be run.
If you are interested in learning more about fence overturning or would like assistance on your next retaining wall project feel free to reach out to our engineering department at engineering@allanblock.com or 800-899-5309 x3.
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Contractor Talk:Allan Block Used for Aesthetics
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Many people love Allan Block and all the features, options, and support that comes with it. With a wide array of products, there is something that can fit just about any situation. You may have wanted to use Allan Block products on a project before but thought site conditions were not suitable. But there are a few wall applications where Allan Block can be used as a facing to achieve the Allan Block look:
Masonry Reinforced Wall
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A masonry application wall with Allan Block creates a rigid structure that is different than a typical SRW’s flexible nature. They are designed exactly like a cantilever concrete retaining wall. The masonry walls need to be filled with concrete and will utilize rebar through the cores. They are unique in how they are designed and built, but they help provide solutions in situations where typical SRW design and construction simply will not work.
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No Fines Concrete Veneer
There are many advantages to using No-Fines-Concrete (NFC). Contractors can build walls quickly and with less excavation in difficult sites to solve a variety of negative site conditions. It can be used to add a veneer to an existing retaining wall to give it an updated look. You can find more information on No Fines Concrete Here.
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Soil Nails
Soil nailing is a construction technique that can be used to treat unstable natural soil slopes or as a construction technique that allows the safe over-steepening of new or existing soil slopes. While this technique works well, the result does not have a nice look. This is a great application where Allan Block can be added in front for a wall that is both structurally sound but also aesthetically pleasing.
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When considering special applications, unusual job sites, or unique reinforcement requirements, contact Allan Block Corporation for engineering and design support. The Allan Block Engineering Department provides assistance to engineering and design professionals worldwide.
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