Technical Newsletter

Allan Block Design Professionals

March 2024

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Our Design Professional ABU Online events were created to help you with your retaining wall needs.

In This Issue

Hot Topic: Vegetation Above a Wall

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A frequently asked question we get from design engineers is, “Are there recommendations for planting vegetation above a retaining wall?” Walls and vegitation are often combined to reduce erosion and for aesthetics, but it must be properly done to not affect the wall stability and to ensure the vegetation will grow. Allan Block worked with the Concrete Masonry & Hardscapes Association (CMHA) and other industry professionals to provide some guidance.

Vegetation recommendations for the top of a retaining wall have been finalized and will be on the CMHA website under Frequently Asked Questions. We want to minimize the disturbance of the retaining wall structure, including the geogrid, so recommendations outlined in SRW-FAQ-003-24 will vary based on the size of the root ball to be planted as well as spacing. For example:

  • The spacing should be greater than 4 times the root ball diameter or a minimum of 5 ft (1.5 m)
  • It is also recommended that the root ball be located at least 5 ft (1.5 m) from the retaining wall.
  • You should also ensure that when a tree matures, the canopy will not hang over the face of the retaining wall.

Vegetation Above Wall

For more information, please refer to SRW-FAQ-003-24 or contact the engineering department at Allan Block.

Alternative Options – Allan Block as a Masonry Application

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Westmoore Developments is a 67-acre development outside Washington DC, where land is at a premium. The Development wanted to maximize the number of townhome units which required multiple retaining walls.

The plans called for the retaining walls to be near the townhomes, detention basins, property lines and existing trees they wanted to preserve. By working with the local Allan Block manufacturer, Nitterhouse Masonry Products, the landscape architect, Land Planning and Design Associates (LPDA) and the land development general contractor, KT Enterprises they were able to come up with a combination of AB Classic and AB Vertical products to overcome the challenges of limited clearance behind several retaining walls.

The majority of the walls were able to follow traditional gravity and/or geogrid reinforced designs and construction using AB Classics. However, due to required wall heights and wall locations, some walls needed to investigate alternate designs, such as Masonry Applications, with the AB Vertical (3 degree) unit to maintain the same stability and aesthetic throughout the property.

Masonry applications utilize the hollow core of the Allan Block units, they install vertical rebar, grout and a cantilever footing below to resist the pressure behind the wall. This solution provided the most economical solution for this project.

Zero Section

When installing this project, care had to be taken when leveling the blocks to keep the setback within construction tolerance without going negative, especially with the AB Vertical units. To ensure proper installation to match the design, KT Enterprises contracted the work to an Allan Block Certified Contractor, Stonebridge Civil.

Check out the full "Alternative Options – Allan Block as a Masonry Application" case study for more in-depth information.

Lake Tulloch

Engineer Talk: Importance of Block Setback in Design

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When you are designing a wall, one of the biggest things to consider is what block setback is feasible with your design. There’re several factors both from a design and construction standpoint that should be in mind when selecting the block for your specific project. At Allan Block, we provide you with three different setback options: 3, 6, and 12 degrees, our AB Vertical, AB Classic, and AB Stones, respectively.

The design of a setback/battered wall is different and there are some important notes from a pressure standpoint to cover. The wall and the sliding wedge are reduced in pressure by the setback from vertical. For design consideration, the setback will change the pressure acting on the wall. A simple example: the figure to the left shows how the amount of retained soil is reduced when a setback is implemented. This means that the weight is reduced which lowers the system total pressure. We minimize the amount of reinforcement compared to a vertical system because a setback adds built in resistance to sliding and overturning failures that can occur on site.

The amount of space you have for a wall when constructed directly impacts how much of a setback is allowed. When designing near utilities or property lines, it can force us to get creative to still fulfill proper grid lengths and internal grid safety factors, such as overstress, pullout, and tensile strength.

As shown in the image to the right, the total depth of the structure increases the setback with a 12-degree block and requires more room for excavation and building.

For more information on our product setbacks and building retaining walls using Allan Block, please visit our website or call the engineering line at 1-800-899-5309.


Tools: Presentation about the Value of SRW and Alternate Reinforcement

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We are thrilled to announce an upcoming presentation on June 20th that promises to unveil the remarkable value of Segmental Retaining Walls (SRW) and the innovative use of alternate reinforcement methods. As pioneers in the industry, it's crucial for us to continually explore and share advancements that elevate the effectiveness and sustainability of our products. This presentation is a testament to our commitment to providing cutting-edge solutions to our valued customers.

In this presentation, you will learn about the multifaceted benefits of SRWs and how alternate reinforcement techniques can further enhance their performance and longevity. Attendees will gain insights into:

  • Enhanced Structural Integrity: Discover how alternate reinforcement methods bolster the structural integrity of SRWs, ensuring they withstand the test of time and environmental pressures.
  • Cost Efficiency: Learn about cost-effective solutions that optimize the use of materials without compromising on strength and durability, ultimately saving both time and money.
  • Design Flexibility: Uncover the versatility of SRWs and how alternate reinforcement techniques expand design possibilities, allowing for tailored solutions to meet various project requirements.

ABU Online Value and Reinforcement

How to Attend Allan Block University (ABU) Online:

We understand that accessibility is key, which is why we're excited to offer this presentation through our Allan Block University (ABU) online platform. Here's how you can attend:

View the current ABU Schedule to see the upcoming webinars occurring for design professionals.

Register for the presentation on June 20th and secure your spot at the time that best fits your schedule. Make sure to mark your calendar for the scheduled date and time of the presentation to join us.

Don't miss your chance to gain valuable insights into the enhanced value of SRWs and the transformative potential of alternate reinforcement methods. Register today and be at the forefront of innovation in the construction industry. Together, let's build a future where sustainability, efficiency, and excellence are the cornerstones of every project

Contractor Talk: When Fences are Needed Above a Retaining Wall

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If your next client is requesting a fence or railing above a retaining wall and you are not sure what to do, have no fear, we have the information to help you! The implementation of a fence or railing above a wall should be considered before the retaining wall has been built and needs to be included in the design of the wall.

Fence posts require concrete forms to be placed within the reinforced zone of the wall. If the retaining wall has already been built you may be required to re-excavate the site to install the concrete forms for the posts, this increases time and money spent on the project. Rather than re-excavating you may choose to use an auger to place the forms. Inevitably, using an auger will result in damage to the geogrid, weakening the reinforced mass. The ideal construction process for a wall with a fence above is to place the concrete forms during the construction of the retaining wall.

The first consideration when designing an above wall fence is the post footing location. The preferred location for a fence footing is a minimum of 3 ft (0.9m) behind the back of the wall. This configuration utilizes the soil mass between the wall and the footing to reduce the overturning forces provided by the fence.

Fence e ft behind

Footing installed 3 ft (0.9 m) from back wall

Footing installed within

Detail for installation of Sleeve-it

If your application requires the fence to be installed closer than 3 ft (0.9 m) or directly behind the wall, a simple solution would be to use Sleeve-It. If you are not going to use Sleeve-It you will need to consider the additional overturning load acting at the top of the wall. Our Top of Wall Fence Overturning Sheet provides information on how to address this case. In any case, no matter the location of the footing a local engineer should be consulted before building your wall.

Fence Directly Behind

Footing installed directly behind

Footing installed within

Footing installed within

If you are interested in learning more about fence overturning or would like assistance with your next retaining wall project, feel free to reach out to our engineering department at or 800-899-5309 x3.

Helpful Documents:

ABU Online

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See Our Live ABU Online Webinars

Our Design Professional ABU Online events were created to help you with your retaining wall needs. Our local production and sales partners will be happy to schedule in person training on any topics you see below (call us if you are looking for those individuals) but feel free to use these to help with immediate needs..

We hope you have joined us in our sessions. Are we missing key training topics you would like to see that we have not covered? Let us know what you think by calling or emailing us.

Design Professionals

Offered on THURSDAYS at 8 AM, 11 AM, 1 PM OR 4 PM CENTRAL TIME (1 hour sessions)

The Value of SRWs vs Alternate Reinforcement Systems

Segmental Retaining Wall Design
Sign up: 7/18

Best Practices for SRW Design
Sign up:8/15

AB Walls 3D+Terraces Basic Tutorial
Sign up:9/19

Water Management and AB Walls 3D+Terraces
Sign up: 3/21

SRW Inspectors Presentation
Sign up: 3/28

Terraces and Global Stability in AB Walls 3D+Terraces
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Seismic Consideration and Above Wall Considerations in AB Walls 3D+Terraces
Sign up: 4/11

Complex Composite Structures and No-Fines Concrete with AB Walls 3D+Terraces
Sign up: 4/18

SRW Architectural Presentation
Sign up: 4/25

GRS/IBS Application
Sign up: 5/2

Submittals and 3D Modeling in AB Walls 3D+Terraces
Sign up: 5/9

AB CADD within the AB Walls Design Software
Sign up: 5/16

AB Fence Design and Installation
Sign up: 5/23

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Allan Block Corporation
7424 W. 78th Street, Bloomington, MN 55439
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