January 23, 2020

How to Design a Fence/Railing Above a Retaining Wall.

Depending on the application and location of the fence/rail, it may affect the retaining wall design with forces at the top of the wall that could cause it to roll over (overturning). Allan Block has created a Fences Above Retaining Walls Tech sheet that covers the different location and installation options.

One way to account for the overturning forces is to use a product called Sleeve-It by Strata that will reroute the forces away from the wall. 

January 16, 2020

How to Prevent Retaining Wall Failure - What do I Need to Know?


Water can be the most destructive element to a retaining wall. Pressure is dramatically increased when water is allowed to saturate the soil or backfill. Wet soil is heavier and loses its cohesion, which adds pressure to the wall. 

To prevent water saturation drainage pathways are added to the site, as well as to the retaining wall to channel water away. These features are one of the most critical steps in designing a wall that will last a lifetime.

Unanticipated Loads

The pressures that are applied to the retaining walls increase as external loads are added on top of the wall. When unanticipated loads are added to a wall structure—such as a truck delivering landscape supplies, or a new structure is added on top of an existing wall—the loads increase.  Even building a retaining wall with the wrong sized compaction equipment can over-stress a wall. When designing a wall, anticipate and design for future requirements that may affect its performance.

Foundation Issues

Just like any building project, the foundation must be strong enough to hold the structure. In some cases, removing poor soils will be required before building. In all cases, proper compaction of the foundation soil is required. When excavating on-site soils, be careful to not over excavate. Any soil that is disturbed or not for a foundation, we recommend compaction. Sometimes, you may encounter a previously excavated area that will need to be properly compacted before construction can begin.

Substandard Construction

Many contractors are looking for short cuts that may save them some time and money. Don’t be surprised that in most cases, you get what you pay for. It’s always a good idea to review our website www.allanblock.com so that you can make sure the contractor follows the proper building steps. Look for a certified Allan Block contractor that has the training and experience to build walls correctly the first time.

January 9, 2020

What are Some Good Layout Ideas for Retaining Walls?

Your front and back yards are extensions of your home, and often leave a lasting impression.  All the more reason to invest a little extra time and effort into designing them into something worth remembering.

A retaining wall in a garden can be for a fundamental or architectural reason, or just a landscape feature.  When you add walls in your gardens, they will look better as a result.  Gardening is a passion for many home owners and expressing their creativity brings lasting satisfaction.  Here are some great layout ideas that will make some outstanding impressions.

Express yourself with Terracing 

If you have rolling hills or slopes in your yard, terraced retaining walls might just be your best friend.  Create more usable space by terracing in your gardens.  This will tame tall slopes and add aesthetic beauty.  Choose an Allan Block Collection that best suits the look and feel of your home and yard.  Enjoy not bending over so far by raising your plantings.  Transform your landscapes into dynamic works of art.

Create a Variety of shapes and sizes

One of the most common mistakes in designing your yard is the lack of variety.  In nature, we see plants and trees that grow naturally in their variety.   A good layout uses walls that vary in size and meander to organize a space.  The same is true with plantings.  Having plantings in mind can modify how you want your walls to look and how to utilize the space created by them. Choose a variety of plants that grow and mature well together. Organize them as a painter brings order to their paintings.  Avoid planting in rows, keep it natural.  Enjoy expressing your creativity with plants and walls.

Contrast is another design tool

Have you noticed that everything tends to look much better as the sun begins to set?  The sun highlights some spots and darkens others as the intensity decreases as it sets.  Contrast is a key to transforming your landscape.  Consider adding a contrasting color to the cap, or just under the cap, of your retaining walls.  Consider plants that contrast each other as the seasons change.  Use contrasting mulch that highlights your planting and walls.

With these endless possibilities in mind, your yard can be transformed into your own personal oasis. Check out our Design Ideas for further inspiration!

January 2, 2020

How do I Extend the Wall Above Grade for a Parapet/Fence?

Very often a retaining wall gets extended to create a seating wall or a short privacy fence.  This can be done in several ways, and some of it will depend on the application or product you are selecting.  I do want to clarify that any fences above the wall will require additional engineering, since you must account for the wind pressure that will be applied.  However, I want to focus on different applications here.
·       We have extended the retaining wall and built a second wall on the back side to create a back-to-back application.  This has been used more on commercial applications, since it is easy to reinforce this parapet for structural concerns.  However, it does take up a little more space. 

·       Another option is to cap your Allan Block retaining wall and then install the AB Courtyard above.  With similar textures and colors, this is a seamless transition.

·       The AB Fieldstone is a two-piece system that allows the user to change the type of anchoring unit and use the same facing elements to build both the retaining wall and the parapet.  This creates a very aesthetically pleasing option and should be considered since the system was designed for this application.  There is a complete section for parapet construction on our website.

·       The last option breaks away from the retaining walls since we are actually using the AB Fence to construct the wall and the fence.  If you are considering a true fence application, this might be the solution for you. With this type of application, engineering would be required to ensure the fence is installed properly as a retaining wall.

December 26, 2019

Determining the Radius of a Curved Wall

You’re building a wall that has a curve in it, but you aren’t sure what the radius of the base row should be. What do you do? Luckily, here at Allan Block we have a few useful tools to help you figure out exactly what your curved wall’s radius should be.
One of the most useful tools for finding your radius is the AB Radius Chart. This handy guide gives you a quick way to estimate the minimum radius that the bottom of wall can be, depending on what block you use and the height of the curve.
AB Radius Chart for Base Course of Curved Retaining Wall
Wall Height
3 ft
(0.9 m)
4 ft
(1.2 m)
5 ft
(1.5 m)
6 ft
(1.8 m)

AB Stones 12° (Ref)

5 ft 3 in
(1.6 m)
5 ft 6 in
(1.7 m)
5 ft 9 in
(1.75 m)
6 ft
(1.8 m)

AB Classic, AB Lite Stone 6° (Ref)
AB Aztec Classic, AB Aztec Lite Stone 6° (Ref)
AB Dover, AB Barcelona 6° (Ref)

4 ft 11 in
(1.5 m)
5 ft 1 in
(1.55 m)
5 ft 4 in
(1.62 m)
5 ft 6 in
(1.7 m)

AB Fieldstone 6° (Ref)
with Short Anchoring Unit (SAU)

6 ft 5 in
(1.95 m)
6 ft 7 in
(2 m)
6 ft 10 in
(2.1 m)
7 ft
(2.13 m)

AB Jumbo Junior, AB Junior Lite 6° (Ref)
AB Aztec Junior, AB Aztec Junior Lite 6° (Ref)
AB Palermo, AB Bordeaux 6° (Ref)

3 ft 5 in
(1.0 m)
3 ft 10 in
(1.16 m)
4 ft 3 in
(1.28 m)
4 ft 7 in
(1.4 m)

Another valuable resource would be the “Curves & Serpentines” page on the Allan Block website. This page will not only give you more information about what factors of the wall will affect its radius, but will also provide useful tips and diagrams showing how to construct your curved walls correctly.

If you look through the two options listed above and still can’t determine what the radius of your wall should be, we suggest that you use our third, and most valuable, resource – your local rep or the the Allan Block Staff. If you call or email in with any questions regarding curves in retaining walls, we will always be here to share our knowledge with you and provide a straight-forward answer for your not-so-straight wall.

December 19, 2019

Is Compaction Needed When Building a Wall?

This seems like a straightforward question, right?  But you would not believe how many walls we get called on that are having problems.  Many of these problems are directly related to lack of compaction.  When starting your wall, the first thing you do is dig out a trench to build your leveling base.  If you dig the trench, and level all the loose material at the bottom without compacting the base of the trench, chances are your wall will see some amount of settlement.  Next, you pour the base rock into the trench to form your base.  If you do not compact the base rock to make it nice, consolidated, and tight, your wall will most likely see some settlement.  Compacting the bottom of the trench and the base material is a key factor in building a quality wall that will not settle.

Now that you have a well compacted base that is level, you start the wall by placing the first course of Allan Block. Fill the cores of the block and behind the block with wall rock, a compactable aggregate. Then, place your 8 inches (2.5 cm) of infill material to be basically level with the top of the block. If you continue to build the wall like this, course by course without compacting the wall rock and infill material, it creates another possibility of settlement.

Notice a theme?

Without compaction your wall will settle.  There is no question about it. 

Settlement can cause lots of complications, some esthetic and some structural.  Esthetic issues are an uneven and out-of-level block course, or even courses of wall that roll forward or backwards, among other things.  Structural issues from settlement behind the wall will put additional “down drag” force on the geogrid layers and could cause significant damage to its life span.

 So, if you have not figured out the answer yet…YES…COMPACTION IS NEEDED WHEN BUILDING ANY SEGMENTAL RETAINING WALL. See our Installation Guides for proper construction methods.

December 12, 2019

What is the AB Dogbone and What is it Used For?

The AB Dogbone is used to connect the facing units of the AB Fieldstone Collection together.  We call them dog bones because they have the shape of a bone.

Typically, we use them for building parapet walls. There are 2 options for building parapet


Where the AB Dogbones connect the facing units together. Easily build corners and parapets
with posts. Offers the smallest width, for straight walls only.


Where the AB Dogbones act as anchors in the wall rock allowing any size width to be created.
Works well for straight and curved walls.

December 5, 2019

Will Allan Block Retaining Walls Perform Well in High Seismic Zones?

Allan Block Segmental Retaining Walls (SRW) are the only SRW products to be tested in full-scale seismic testing on one of the world’s largest shake tables located in Tsukuba, Japan.  The tests were conducted in the fall of 2002, and were tested at loads that exceeded the 7.2 magnitude of the Kobe, Japan earthquake in January of 1995.  To read more about the tests, see the test report (http://www.allanblock.com/literature/PDF/seismicreport1.pdf ) or the Executive Summary (http://www.allanblock.com/literature/PDF/seismicreport2.pdf

The results of the tests performed by researchers from Columbia University, University of Delaware and the Science Institute of Japan were so remarkable that in only 5 short years, all viable design codes in North America accepted the results and modified their seismic design calculations.

The key to the incredible performance of an Allan Block segmental wall under seismic loading, is the flexible nature of the system and the remarkable facial strength and stability of the facing.  The blocks are assembled with no need for the mortar that concrete masonry block walls require, and have a virtually continuous connection to the horizontal geogrid layers. For more information on geogrid reinforcement, see our website: http://www.allanblock.com/retaining-walls/reinforced-installation.aspx .  The reinforced soil mass faced with Allan Block easily handles the seismic events by its ability to flex and move with the seismic waves, while remaining fully intact and stable.  For more on seismic loading and design consideration, see the Best Practices for Segmental Retaining Wall Design.

                                       Allan Block Retaining Wall Seismic Test Video

November 28, 2019

What Type of Equipment is Needed to Build a Concrete Fence?

Let’s face it, having the right tool makes every project easier.  This is no exception when building an AB Fence.  You will be digging holes for footings, moving dirt and block, compacting dirt, mixing concrete and even cutting concrete block.  The list of tools that is starting to go through your head should be quite long.  

Most contractors will have most of these tools already and even the above average DIYer will have a good start on this list.  However, the ones that will make this job easier are the power tools consisting of a Bobcat with an 24-inch auger attachment used to drill the footings, a laser level to locate proper elevation and a concrete vibrator used to consolidate the concrete and ensure stability.  Obviously, you may be cutting block so having a saw with a diamond blade is very important.

Constructing an AB Fence is not difficult, but I would recommend an experienced DIYer or hiring a certified contractor to tackle the job. 

November 21, 2019

How Do I Figure Out How Many AB Fence Blocks I Need?

Any good handyman or Do-It-Yourselfer knows that you need proper tools when you want a job well done.  That is why Allan Block has an estimating tool that can be downloaded at allanblock.com or click on this link (AB Estimating Tool For Retaining Walls, Patio Walls & Fences). 

To get started on your estimation, you need to deliberate the final aesthetics of the project. Here are some things to consider:

Standard Block Fence with Iron Fencing Above
  • What is the height of the fence?
  • What is the overall length?
  • Are there corners or openings that need to be considered?
  • Will you be finishing the posts one block higher than the panels as we recommend, or even taller to account for iron or metal fencing?
  • Are you constructing an Ashlar Pattern panel, or just using Standard Panel Block? 

Ashlar Pattern Panel

Once you have answers to these questions, you can use the AB Estimating Tool and get the amount of block you need.  Obviously, there are always people to help you.  Click on “Find a Store” at www.allanblock.com and talk to your local manufacturer for any questions you may have.  Or send us an email at engineering@allanblock.com