Estimating the right amount of materials is an important part of any project. It assures maximum profitability and that you do not run short of materials mid-project which can create other problems such as project delays. Accurate estimating is good overall project management and there are many available manufacturer resources to help you through the process. These resources include design and estimating manuals, installation training classes and videos and a dedicated sales representative to assist you with your specific project questions.

In this article, we will review the information you need to create your materials' estimate as well as 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.

"To get started, gather information about the wall," Barnhart explains. Good questions to collect needed information include:

• How high above grade will the finished wall be?
• Will this wall need geosynthetic reinforcement?
• What'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?

"The information you receive from these questions allows you to determine what materials you will be using," she says. "Sometimes the retaining wall product selected will be based upon property owner's preference, and sometimes the project itself will drive the product to be used. Some walls will require an engineer's involvement. Accessories such like drainage pipe should also be considered."

The success of the SRW project rests in a level foundation. Here, the rear lip of the stone is removed so it will lay flat on the leveling pad. By cutting stones, they can be placed in a staggered relationship.

For our project example, the wall will be built with Anchor Highland Stone(r). 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, delivers a natural look while the patented design allows you to efficiently build a low-maintenance, durable retaining wall.

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

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.

Project Example

Let's say you have a project that is 50 linear feet long and four-feet high. Based on the preceding questions, you and your customer have determined the Anchor Highland Stone system is the best product for the project. You have been to the site and determined that there is no slope at the top or toe, no surcharge and no water. The soils are a combination of silt/clay and sand. The leveling pad will be 24 inches wide. The drainage column is 12 inches wide.

"To determine the quantity of Anchor Highland Stone you need, the Anchor Estimating and Installation Manual is an excellent resource," Bodie explains. "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's worksheet, calculate our materials needed as follows:

Materials Quantity

• 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

Now that you've estimated the materials needed for the project, Bodie and Barnhart recommend that you follow the following steps for a smooth installation.

Step One - Stake Out The Wall

Stake out the wall'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.

Using a carpenter's level, the base course was leveled front-to-back and side-to-side.

Step Two - Leveling Pad

An aggregate leveling pad is made of a good compactible 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.

18-inch stones are used for the base course of the SRW, which is buried when the project is complete.

Step Three - Base Course

In this step, the base course is laid, one of the most important steps in the construction process. First, run a string line to align the wall units. Begin laying block at the lowest elevation of the wall. Remove the rear lip of the block so that is will lie flat on the leveling pad. Place the blocks side-by-side, flush against each other, and make sure the blocks are in full contact with the leveling pad.

You should level the blocks front to back and side to side. If the wall site is on an incline, don't slope the blocks, step them up so that 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's why there are more 18-inch stones on the materials list.

Step Four - Next Lift Construction

When you begin the next lift, you can 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 'stagger' 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.

To keep the wall bond, place stones in a staggered relationship to the underlying course, making sure the joints on top do not align with the row below.

Step Seven - Reinforcement

Your wall construction plan will show which courses need reinforcement. Before you lay reinforcement, clean any debris off the top layer of blocks. Measure and cut the reinforcement based on the plan design lengths. The reinforcement has a design strength direction. This must be laid perpendicular to the wall.

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 your 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.