Estimating the right amount of materials is a critically important part of any project. Correct estimating helps assure maximum profitability for the contractor, and prevents shortfalls of materials in mid-project, which invariably creates problems and project delays. Accurate estimating is clearly good overall project management. There are many available resource guides: design and estimating manuals; installation training classes; videos; and dedicated sales representatives to assist with specific project questions.

In this article, we will review the information needed to create an estimate of materials and discuss installation steps. Richard Bodie, the national sales director for Pavestone Company, and Lynn Barnhart, landscape market manager for Anchor Wall Systems, provide the segmental retaining wall expertise for this article.

?EUR??,,????'??To get started, gather information about the wall,?EUR??,,????'?? Barnhart explains.

Good Questions to Ask and Consider.

For our project example, the wall will be built with Anchor Highland Stone®. It is a multi-piece system with a bullet crunch face. The different size stones modulate, or fit together, to allow a total random look. The natural face is popular and delivers a natural look. The patented design allows you to efficiently build a low-maintenance, durable retaining wall.

?EUR??,,????'??Highland Stone is a great choice for many wall projects as it is easy to install,?EUR??,,????'?? Barnhart says. ?EUR??,,????'??The contractor can build a four-foot gravity wall; taller walls can be achieved with engineering and reinforcement.?EUR??,,????'??

Project Example

?EUR??,,????'??To determine the quantity of Anchor Highland Stone needed, the Anchor Estimating and Installation Manual is an excellent resource,?EUR??,,????'?? Bodie explains. ?EUR??,,????'??Using this manual as a guide, we determine the materials needed for the 200-square foot wall (four feet x 50 feet) and, using the manual?EUR??,,????'???s worksheet, calculate our materials needed as follows:

Once the materials are estimated for the project, Bodie and Barnhart recommend the following steps for a smooth installation.

Step One – Stake out the Wall

Stake out the wall?EUR??,,????'???s placement. Excavate for the leveling pad to the lines and grades shown on the approved plans and excavate enough soil behind the wall for the reinforcement material. The trench for the leveling pad should be a minimum width of 24 inches and 12 inches deep.

Step Two – Leveling Pad

An aggregate leveling pad is made of a good, compactable base material of 3/4 inch minus with fines. The pad must extend six inches in front of and behind the first course of block and be at least six inches deep. Compact the aggregate and make sure it is level.

Step Three – Base Course

The blocks should be leveled front to back and side to side. If the wall site is on an incline, the blocks should not be slopped, but stepped, so they remain consistently level. Check for proper alignment before moving on to the next step. We recommend using the 18-inch unit for the base course. That?EUR??,,????'???s why there are more 18-inch stones on the materials list.

Step Four – Next Lift Construction

For the next lift, install the Anchor Highland Stone system in any combination of stones. Keep the wall bond by placing stones in a staggered relationship to the course below; this means that the stones should be placed in a way so that the joints on the row above do not line up with the joints below, creating a staggered effect.

For best results, use a filter fabric, which should be placed directly behind the wall extending from the bottom of the base course to the middle of the top course. This will minimize material coming through the rough-hewn face.

Step Five – Drainage Design

Drainage design is unique for each project. Place the drain tile as low as possible behind the wall so water drains down and away from the wall into a storm drain or to an area lower than the wall. Fill the area behind the blocks with drainage aggregate at least 12 inches from the wall. For best results, cover the drain tile with a geotextile sock that acts as a filter. Drain tile outlets should be space no more than 75 feet apart and at low points of the wall.

Step Six – Compaction

Shovel the in-fill soil behind the drainage aggregate and compact the in-fill with a hand-operated compactor. Make sure the aggregate is level with or slightly below the top of the base course. Place soil in front of base course so that it is buried.

Step Seven – Reinforcement

Place the front edge of the material on the top course, two inches from the face of the block. Lay the next course of blocks to secure the reinforcement. To keep it from wrinkling, pull the reinforcement taut and pin the back edge in place with stakes or staples. Add drainage aggregate behind the blocks, then add the in-fill soil and compact it. A minimum of six inches of backfill in required prior to operating vehicles on the reinforcement. And remember, avoid sudden turning or braking.

Step Eight – Finish Grade and Surface Drainage

Protect the wall with a finished grade at the top and bottom. To ensure proper water drainage away from the wall, use six inches of soil with low permeability. This will minimize water seeping into the soil and drainage aggregate behind the wall.

Step Nine – Site Cleaning and Restoration

Brush off the wall and pick up any debris left form the construction process. Planting vegetation in front of and on top of the wall will help reduce the chance of erosion.

The segmental retaining wall market continues to grow in popularity due to the availability of choices in manufactured stone colors, shapes and textures. The efficiency and ease of installation make them accessible to landscape contracting firms of all sizes.

• How high above grade will the finished wall be?
• Will this wall need geosynthetic reinforcement?
• What?EUR??,,????'???s going on around the wall?
• Are there load issues to consider, such as vehicular traffic?
• Is there a slope at the toe, or bottom of the wall?
• Is there a slope at the top?
• Is there water involved?

Materials List:

• Wall stones and caps
• Geosynthetic reinforcement (if conditions require it or the wall is more than four-feet tall)
• Filter fabric
• Aggregate for the base course leveling pad (3/4 minus with fines)
• Drainage aggregate for back fill (1 minus crush stone or granular fill, #57 stone)
• Drain pipe
• Backfill material
• Concrete adhesive for cap stones.

Materials Quantity for 200 sq.ft. wall

• 18" Stones needed: 151
• 12" Stones needed: 117
• 6" Stones needed: 117
• Cap Stones needed: 41
• Geosynthetic reinforcement (two 4-foot layers x 50 feet) needed: 45 square yards
• Filter fabric needed: two rolls
• Drainage pipe needed: 50 linear feet
• Leveling pad stone (3/4" minus fine) needed: three tons (1.94 cubic yards)
• Drainage aggregate (1" minus stone) needed: 12 tons (7.41 cubic yards)
• Concrete adhesive needed: three tubes