Can a Concrete Leveling Pad be Used for an Allan Block Wall?

Engineers and installers often wonder whether a concrete leveling pad may be superior to gravel.  While a rigid foundation isn’t what we’d typically recommend, it can be used provided the engineer okays it.  Unlike gravel, however, this footing may crack and break apart as the wall shifts with moisture and temperature changes.  Concrete will also be more expensive and typically add to labor, so it should be avoided in most applications.  If an existing concrete footing must be used, then the bottom course of block must be tied to the footing using steel rods.  This eliminates concerns of potential sliding of the wall.

Most Allan Block walls are designed with a gravel base which is a minimum of 6 inches in depth, and 2 feet in width (15cm and 60cm).  There are benefits to using this type of footing.  One major benefit in cold climates is that gravel is not negatively impacted by movement caused by freeze-thaw.  To learn more about our recommended base, visit the base installation guide.

What Kind of Material do I Use to Fill the Blocks & the Drainage Behind the Blocks?

A long lasting and great looking retaining wall project begins by selecting the proper material to use during construction of the wall.  After you have selected the proper block to use, you may find yourself wondering “what do I put within and behind the blocks?”

Typical Section

Wall Rock

To build a quality wall, use a clean, granular rock (to a depth of at least 12” (30.5cm) behind the block) to ensure better drainage and compaction to improve the overall performance of your finished wall.  We refer to the material used within and behind the block as Wall Rock. Crushed or smooth stone, well graded, compactable aggregate, ranging in size from 0.25 in. to 1.5 in. (6 to 38 mm) is the ideal wall rock size.  Your AB Dealer will most likely have what you need.

For complete installation details, check out our installation guides.

How Does Geogrid Work on Curves and Corners?

If you are building a reinforced retaining wall, there is a good chance you will have either curves or corners in your design.  How do you maintain the reinforced soil when building curves or corners? 

When building curves, the geogrid reinforcement needs to cover 100% of the curve. If it is an inside curve, the grid will be placed around the curve with gaps in between - the gaps will be filled in with grid on the next course.

For outside curves, the grid will be placed all on the same course, overlapping in the curve.  Wall rock will need to be added between the overlapping portions of the grid, so the pieces of grid don’t rub together.

For inside corners, the reinforcement grid needs to extend past the corner in each direction on alternate courses for stability the corner. 

For outside corners, the grid is simply rolled out along the wall in one direction on one course and in the other direction on the next.  While the concepts are pretty simple you will want to make sure you install correctly as corners are usually the most susceptible to sagging or wall failure. Best Practices for Segmental Retaining Walls gives detailed information on how to handle proper gridding of corners and curves.

 To be sure you get it down just right – read all about it in the Allan Block Installation Guide.

What do I need to know as I plan/design my retaining wall?

There is a lot of planning that goes into a retaining wall design when things begin to start moving forward.  To provide more information, you can visit the Allan Block Residential Retaining Wall Manual to help organize and formulate your plan. To summarize some of the main talking points, lets break it down into the following 5 items:

           Soils – What type of soils do you have at your project?  Are they sandy? Clay? Gravel?  This can increase the pressure on the wall, and require additional reinforcement depending on the height of your wall.  Since the purpose of the wall is to retain soil, this remains one of the most important aspects in the design.

           Slopes – Are there slopes above the retaining wall?  If the grade is going to slope above the wall, this is an added load and therefore may also require additional reinforcement.  Slopes above a retaining wall remain one of the largest loads possible; the steeper the slope, the more load the wall will carry.  What about slopes below the wall?  If there is a slope below the wall, then you will want to verify with your local engineer that global stability isn’t a concern, or that your wall will remain stable.  Slopes above and below a wall are an immediate red flag for a global stability concern.

          Surcharges – A surcharge can be anything above the wall that adds weight to the soil behind it.  This can be a parking lot, a driveway, a building, equipment, snow loads, or as mentioned above, slopes.  Anything that may be placed above the wall with a sizable mass to it is considered a surcharge.

      Water Management – Water is the #1 reason why walls fail.  With that being said, you will want to make sure your grades around the retaining wall don’t bring water towards it.  Instead, you’ll want to use berms and swales to guide water around the wall, keeping the soil behind it as dry as possible.

Examples of permeability in different soils and gravel.

      Retained Height – The height of the wall plays a major role.  As the height increases, more pressure is exerted on the wall.  Many local building codes govern when a retaining wall needs engineering and permitting, but even small walls can have issues if the previous notes aren’t planned for and taken into consideration.  As the wall increases in height, you will want to make sure you have additional reinforcement to make sure your wall lasts a lifetime!

These items may not be the only items to check and consider prior to construction of your retaining wall, but it is a quick list to run down as you begin to plan your wall project.

Count the Yard: Estimating Your Outdoor Project Materials

Are you thinking about building your next outdoor living space with Allan Block products? Do you have an idea what you want to build, but you don’t know how much material to buy? Allan Block has some great software applications to help you take your project to that next step.

AB Estimating Tool

Estimate all your Allan Block projects in one place with the AB Estimating Tool. This simple material estimator for retaining walls, patio walls, and concrete fences allows you to quickly and efficiently estimate the materials needed for large and small retaining walls, AB Courtyard patio walls and AB Fence sound and security fences (available in English and metric units.)

The AB Estimating Tool is a great resource for quickly generating material quantities that you can take straight to a contractor or hardscapes dealer to get your project started. Are you looking for something a little more visual? Do you want to lay out your project before you get a material estimate together?

With the AB Courtyard application you can choose from a variety of pre-designed patio packages or create your own patio design and receive project plans, elevation designs, material estimates, and installation instructions. You can even draw your project in 3D  (available in English and metric units.)

Ab Courtyard App

The AB Courtyard application walks you through the entire patio design process from start to finish. You can even watch step-by-step videos on the whole installation procedure.