Landscape Newsletter Issue 6
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Terraced Garden Tackles Troublesome Hillside

The Challenge

Building a new home can be exciting and often challenging. This hillside lot was indeed a challenge for the homeowners building in a new development. They needed to reshape the slope in front of their home and gain more usable land for a driveway leading to the front entrance.

The Solution

To manage the 8 ft. (2.4 m) change in grade and create a pleasing landscape, Hardscape Construction Inc., suggested a terraced retaining wall rather than one large wall. They advised the homeowners that two terraced walls with a planting area between them would soften the hill and add drama to the driveway entrance.

AB Dash of Ashlar

"I’m pleased with the results. We took a challenging lot and created a beautifully landscaped driveway entrance".
- Hardscape Construction Inc.
Allan Block using a small amount of Ashlar Pattern in a retaining wall

 The homeowners loved the idea of a terraced flower garden, but needed to keep the costs down. They worked with the contractor to create a design that was both economical and distinct. They used AB Stones for constructing the terraced walls and added a "Dash of Ashlar" to create a beautiful accent texture. With 20% of the wall being the Ashlar Blend pattern, they were able to keep overall costs down while creating a truly unique design.

Engineering & Construction

By keeping the walls under 4 ft. (1.22 m), using AB Stones and laying out the terraces to achieve proper separation, they provided a cost effective solution for developing the site. The contractor describes the construction process, "Because this was a new development with previously excavated soils, we wanted to make sure the walls would not settle over time. So we re-excavated and compacted the base soils before beginning construction. Excavating for the spacing between the walls and compacting the infill soils had to be done carefully. Although difficult, it was necessary to ensure proper long-term performance of the walls.”

Conclusion

The homeowners are delighted with the project. "Hardscape Construction did a very professional job from start to finish. Even with the extra effort they made to ensure the walls were built on stable ground, they completed the entire project in less than 10 days. Today, 8 years later, you can tell they did a great job because the wall looks as good as the day it was finished."

 Allan Block Dash of Ashlar

Spice Up Your Wall with a "Dash of Ashlar"
To give your AB Stones and AB Classic walls eye-stopping design and visual interest, try adding a small area of patterned blocks. It's easy. Using the different block shapes in the AB Ashlar Collection, you can easily build random or "AB Ashlar Blend" patterns into your wall. The photo shows how simple it is to transition in and out of an AB Ashlar Blend pattern. For more information on building AB Ashlar Blend retaining walls, ask your AB Dealer for a copy of the AB Installation Guide. AB Dash of Ashlar wall

Building Terraced Walls
Landscape designs are often more attractive when they include smaller, terraced walls rather than one large wall. Terraced walls can create more usable space, build raised gardens, help prevent erosion and add interest to your landscape.

Plan

Determine the spacing
The spacing and height of terraces will affect the overall design and engineering of your project. Choose the wall layout that best suits your project requirements.


Plan A: One wall
Attain more usable space
above or below the wall.

- Larger walls may need more reinforcement.


Plan B: Two walls, spacing less than 2H1
Soften hillsides, create planters
and add more usable space.

- Tightly spaced walls may need reinforcement as they do not act independently.

Plan C: Two independent walls, spacing greater than 2H1
Create manageable hillsides.

- May reduce or eliminate the need for reinforcement.
- Can design each wall seperately.

Reinforced retaining wall showing slope

AB gravity terraced Wall showing slope

AB reinforced terraced Wall showing slope

Terraces and Structure
Building a series of walls on a slope requires careful planning for the structure. Follow this simple set of rules.

When the walls are spaced far enough apart they are engineered as two independent retaining walls.

The height of the upper wall is equal or less than the height of the bottom wall and the distance between the walls is at least twice the height of the bottom wall.






As the upper wall moves closer to the lower wall, it adds pressure (surcharge) to the lower wall.

The lower wall will need to be engineered to account for the added weight and pressure, and extra reinforcement may be required.




Global Stability

As the size of the slope gets bigger the overall stability of the entire terraced wall structure becomes important. Engineers call this “global stability”. If the total height of the terraced slope is greater than 6 ft. (1.8 m) contact your local Allan Block dealer or engineering professional for design assistance.

 AB Terrace Rule

Multiple retaining walls with grid

Global stability

Design
Design the shape for beauty and function

Consider what will fill the space between terraced walls. Will it be used for plantings, filled with decorative rock or covered with sod? Terraced walls provide built-in edging that minimizes trimming and maintenance. Design the shape of terraced walls to compliment the surrounding architecture and landscape.

  • Straight walls create a formal, structured look
 Terraced ashlar pattern wall
  • Flowing curves have a more natural feel, provide lots of planting pockets and create a softer look.

    Irrigation is often included when incorporating a planter. Ensure that your plan includes provisions for water management.
 Beautiful curves with planter

Build
Build on Solid Ground

  • The most important element in building terraces is soil compaction. Building on poor, uncompacted soil will result in settling of the upper walls. Although lower terraced walls are typically built on solid ground, upper walls are often built on soils that have been disturbed in the construction process. To ensure the stability of these soils, they should be removed down to solid ground and carefully reinstalled and compacted.
  • To achieve proper compaction there are two different techniques that work well. One way is to remove soft or poor soil and replace them with wall rock and compact in 8 in. (200 mm) lifts. Another way is to compact the onsite soils in shorter lifts. When using onsite soils, we recommend no more than a 4 in. (100 mm) lift. Good compaction is the key to minimizing settlement over time.

Plan ahead for walls that split into terraces. The area immediately behind the lower wall will require extra attention to ensure proper base preparation for the new wall above.

AB Stones with plantings abov
Proper Compaction Proper Compaction when wall splits away
Construction Equipment
  • Use hand operated plate compaction equipment on the block and within 3 ft (1 m) of the back of the wall. All heavier equipment must be kept at least 3 ft (1 m) from the back of the wall. Wall designs typically do not account for surcharges from heavy compaction equipment. Even a properly installed and compacted wall will rotate forward when extreme surcharges from heavy equipment are applied to the top of the wall during construction or final grading.
 Proper Compaction Area

AB STONES - Proven Performer and “Everyday Hero”
With the March Madness sporting frenzy behind us and baseball now in full swing, we are all familiar with the difference between “superstars” and "everyday heroes". Did you know that the everyday hero in the Allan Block product lineup is AB Stones? Take a look at the stats and you'll understand why:

Speed & Efficiency - The multi-purpose AB Stones installs quickly and efficiently.

Hard Working - Typically you can build AB Stones gravity walls higher than you can with other stackable blocks. Gravity walls rely on the weight and setback of the wall to retain the soil and do not require any geogrid soil reinforcement. Due to the greater setback of 12° AB Stones it simply holds up more unreinforced soil than the 6° AB Classic or the 3° AB Three. See below for details.

AB Stones

  • 8 in. H x 12 in. D x 18 in. L
    (200mm H x 300mm D x 455mm L)
  • 75 lbs (34kg)
  • 12° Setback
Specifications are approximate. Contact your AB dealer for exact specifications.


 AB Stones

Typical Section
Our signature block is the best choice for basic wall construction. AB Stones are the most efficient, easy-to-stack full size blocks on the market.

Competitive - Based on installation speed and setback, AB Stones outperforms all other wall products and its durability and cost-effectiveness far exceeds that of treated timber walls.

Bang for the Buck - When considering it's efficiency, strength and simplicity, AB Stones gives you great value.


Build taller walls without geogrid reinforcement.
Table Note
  • No surcharge
  • Level slope above wall
  • Walls that exceed these heights will need reinforcement
 AB Stones front entryway