Retaining Walls

There are a lot of factors that are reflected in cost. First, you need to determine what type of wall is best for your application. For example, a simple garden wall to edge your flower beds would use different materials and approach than a sophisticated retaining wall with drainage to provide an entire property with a level area.

There are many options to choose from when selecting a retaining wall. They range from boulder walls, to retaining wall masonry block. The type of application will typically dictate what type of wall is suitable for your application. This is why it is very important to choose a professional to advise you on the type wall needed. Our team is comprised of experts in this field and can advise you on the proper wall for your application.

Aside from the type of wall and considering the different types of applications, most contractors will price a retaining wall project by using a price per square foot method. That being said an appropriate price range would be between $20-$40 per square foot installed again factoring in the type of wall and application.

Different towns/cities have different requirements when it comes to retaining walls. Most towns/cities do not require a construction permit if the wall is under 4ft in height. However, it is important to contact town hall prior to any project to ensure you are able to start your project.

Not all retaining walls need plans. However, depending of the regulations on permitting in your area most municipalities will require plans if a construction permit is required.

Site Prep

Being prepared with the proper tools and equipment before you begin a retaining wall project is important. Here are some other items to consider before you get started.

Site Access

When planning your project, make sure you can access your wall site with construction equipment and materials. For sites with restricted access, plan out where you will stage and store your block, wall rock and other materials.

Wall Rock Wall

Rock To build a quality wall, use a clean, granular rock underneath the base course to create a firm foundation for your project. Good drainage and compaction will add to the quality and performance of your finished wall. We refer to the material used for the base, 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.

Tools & Equipment

You need to have the proper tools on hand. Remember: Safety always comes first. Hand tools, safety glasses, gloves, dust mask, ear protection, knee pads, 4’ level, torpedo level, tape measure, string line, chisel, hand tamper, dead blow hammer, shims, broom, round and square shovel. Power tools, plate compactor, concrete saw with diamond blade, skid loader, transit/site level. Rental equipment plate compactors, concrete saws, skid loaders and transit levels are very useful when building retaining walls.

Compaction

Compact in 8 in. (200 mm) lifts, one course at a time Keep all heavy equipment at least 3 ft. (0.9m) away from the back of the blocks Proper placement and compaction of the infill soils is critical. The most important step in getting proper compaction is the placement of the soil in “lifts”. Compacting in lifts, or layers, of less than 8 in. (200 mm) will facilitate quality compaction. Placement and compaction in lifts that exceed 8 in. (200 mm) will result in less than adequate soil strength. Compaction equipment must be sized according to the type of material being compacted. Always backfill and compact after each course of block is placed. Consult with a local equipment supplier to ensure that proper compaction equipment is used. The consolidation zone runs from the back of the block back 3 ft. (0.9 m) into the infill soil. Only walk behind plate compaction equipment is allowed within the consolidation zone. A minimum of two passes with a walk behind plate compactor is required, starting on top of the block and compacting in paths that run parallel with the wall to the back of the excavated area.

Preparation

Base Preparation

To start your layout, place stakes to represent the location of the front of the retaining wall. Using a string line or paint, mark out the entire length. A garden hose is an excellent tool to use when laying out curved walls. Excavate the area by removing all surface vegetation and organic materials from the area. These cannot be used as backfill material. If reinforcement is needed excavate behind the wall to accommodate the design length of the geogrid. Refer to your approved plans for exact length. Starting at the lowest point, dig a base trench the length of the wall. More information on retaining walls where the base trench steps up a slope. Retaining Wall Base Trench Dig a base trench 24 in. (600 mm) wide the length of the wall.** The depth of the trench will be 6 in. (150 mm) plus an additional 1 in. (25 mm) for each 1 ft (300 mm) of wall height for the amount or buried block that is needed.** Compact the base trench making a minimum of two passes with a walk behind plate compactor. Foundation soils at the bottom of the base trench must be firm and solid. If the soils are made up of heavy clay or wet soils, or the areas have been previously excavated, remove this material and replace with a granular material, compacting in 8 in.(200mm) liffts or less. **For walls under 4 ft (1.2 m) dig the base trench 18 in. wide (460 mm) and 4 in. deep (100 mm) plus additional to account for the amount of buried block needed.

Base Material

How to prepare the base A drain pipe is required for any reinforced wall or any wall over 4 ft. (1.2 m) tall. Place the drain pipe at the lowest possible point toward the back of the trench and vent to daylight every 50 ft. (15 m). More information on drainage and water management. Place a minimum of 6 in. (150 mm) of wall rock in the base trench and rake smooth. Compact the wall rock making a minimum of two passes with a plate compactor. Check the entire length for level, and adjust as needed

Retaining Walls with Geogrid

What is Geogrid? Geogrids are flexible, synthetic meshes which are manufactured specifically for slope stabilization and earth retention. These “grids” are available in a variety of materials, sizes and strengths. They can be made of high tensile strength plastics or woven polyester yarns and are typically packaged at the factory in rolls. See the importance of reinforcement in your retaining wall with this sand castle demonstration. Use the Soil Reinforcement Chart to determine the size of AB Grid you will need and how many layers your retaining wall requires. How Grid Works The sand castle test takes two cylinders of soil and applies vertical force to see how the soil performs. The first cylinder is just compacted material. The second is also compacted material with the addition of mesh screens to simulate the use of geogrid reinforcement.

Finishing a Retaining Wall

Install filter fabric Filter fabric is used on top of the top course of blocks and below the caps to cover the back of the AB Fieldstone anchoring units. This will allow plantable soil to be placed flush against the cap unit.

• Place a strip of filter fabric along the top of the AB Fieldstone anchoring units on the top course of wall. Position so that the fabric starts at the back of the AB Fieldstone facing unit and goes over the AB Fieldstone anchoring unit and down along the back of the anchoring unit.
• Be sure to leave the top surface of the facing unit exposed so that the cap sealant can be placed on the facing unit.
• Finish the wall with AB Capstones. Place the first capstone on the wall to include a 1.5 – 2 in. (40 – 50 mm) overhang.
• Run a string line the length of wall to mark placement of additional capstones.
• To get a consistent point, use the 45° chamfers at the end of each cap as alignment points for string line.
• Use a flexible masonry adhesive, NP1 or equivalent, to secure the capstones in place. Put a small bead of sealant along the sides of the caps as well.
• Backfill behind the last course and behind the AB Capstone with impermeable fill to allow for planting up to the back of the wall.

Retaining walls is not all that we do. Here is a list of services offered:

• Patios
• Walkways
• Walls
• Outdoor kitchens
• Custom Masonry
• Pools
• Outdoor lighting
• Drainage
• Site work
• Tree Work
• Plating
• Landscape design
• Stairs and Steps
• Sod and seeding
• Driveways and walkways
• Excavation
• Outdoor living areas
• Firepits and fireplaces
• Total Property Renovations