Tools of the Trade: SRW Installation Methods

By Tyler Matys and Allison Uher

Retaining walls have become a mainstay in the landscape construction business over the years. Segmental retaining walls (SRWs) in particular have been lucrative for well-educated and experienced contractors due to their relative ease and speed of installation, as they do not require an expensive poured-concrete footing in most cases, and there is no need to apply mortar. Some manufacturers have made these walls even simpler to install by producing solid, self-aligning units (no need to waste time filling the cores) that don?EUR??,,????'???t require any additional pins or clips.

Segmental retaining wall systems can be broadly divided into two main categories:

1. Hand Placed
2. Machine Installed

Depending on the scope of your project and other situational factors that may come into play, you may find that it is more cost-effective to choose an SRW system that is machine-placed. This article will discuss the benefits of machine-installed systems, and provide you with tips for installing them.

Broadly defined, machine-placed systems are characterized mainly by their massive size and weight. Typical machine-installed systems may range between 400 and 1,700 pounds. In most cases, these units are placed using a simple clamp device. The clamp and block are lifted with common construction equipment such as an excavator. Despite their large size, some machine-placed systems have a highly aesthetic split-rock appearance, making them suitable for a wide range of applications, from residential to commercial.

A JCB 407 articulated wheel loader places SRW units using a clamp device. A typical machine-placed SRW segment can range between 400 and 1,700 pounds.

One of the major benefits of machine-installed systems is increased efficiency and productivity. These larger systems should allow you to place more square footage per day when compared to hand-placed installation, due in part to the larger actual unit size, but also because of the increased speed of the machines. This means less dependence on the energy and physical strength of your employees - factors that often will slow a project down and waste valuable time, and in turn, money. Reliance on the energy level/capacity of your workers adds another level of variability to estimation, speed of installation, and scheduling. Remember that simplicity reduces variability. If you eliminate some of the more difficult and time-consuming tasks from the shoulders of your employees, it is easier for you to estimate the speed and therefore the cost of construction. To give you an idea of how reducing labor costs can reduce the total project cost, a recent article in an industry publication estimated labor as 55-65percent of the total cost of a hand-placed SRW installation.

A tractor trailer delivery truck with a boom and clamp make for quick installation.

An equally important reason to select a machine-assisted SRW is to protect the health and safety of your employees. The National Institute for Occupational Safety and Health (NIOSH) has recently lowered the recommended acceptable lifting weight of an industrial worker to well below the single unit weight of many hand-placed systems. Selecting a machine-placed system will let the equipment do the heavy lifting, protecting your workers from job-related injuries and reducing costly down-time.

Another consideration with regard to your workforce is the availability of manual laborers. Our conversations with contractors in various areas of the United States and Canada seem to indicate that the market has recently been showing a downward trend in the availability of manual labor. The consensus among landscape contractors across the continent is that a good man is hard to find, and when you do, he may be tough to keep! One possible solution to this potential shortage of workers is to move some of the brute lifting to the backs of machines.

A worker uses a Hilti rotary hammer drill with a 24 in. concrete carbide-tipped drill bit to core-drill handrails and fences. Workers should be well-versed in the proper use of such machines and related equipment and vehicles.

Beyond the aforementioned effects on labor, a machine-laid SRW may have several other advantages that will save you time and money, or will allow for a more seamless integration with other landscape features.

One structural advantage is the additional stability inherent with larger units. A greater mass will tend to better compensate for the potential variability of site conditions. Larger SRW systems will be less sensitive to overcompaction or the presence of heavy machinery behind the wall facing, or other minor contractor error.

Larger retaining wall systems can also be helpful because they incorporate other structural items well. Poured-in-place crash barriers, flexible steel beam guardrails, and wood fences are all easy to combine with a machine-laid wall. Many contractors appreciate the ability to core-drill handrails and fences directly into the wall?EUR??,,????'??+a feature that is often not available with some smaller, hand-placed wall systems.

Machine-laid SRWs can incorporate such structural items as wood fencing, a feature often not available with some smaller hand-placed SRWs.

Due to their much greater unit-weight and size, these larger SRWs are more resistant to vandalism and damage, an unfortunate fact of life in public areas.

Another benefit of larger SRW systems is that they may minimize your excavation costs. Because of their larger unit dimensions and weight, they can in many cases be constructed as conventional gravity walls (not requiring geogrid reinforcement). Because the wall units are better able to rely on their own gravity for stability, the need to lay geogrid is often eliminated, thereby reducing the amount of excavation to be done on-site. Any type of segmental retaining wall system will bring added dimension and beauty to your landscaping project; even the smaller, more ornamental garden wall will add charm and a finished look to your design.

Tyler Matys is the manager of engineering design at Risi Stone Systems. Allison Uher takes care of the marketing and communications for Risi Stone Systems.

Tips & Techniques

• Ensure all workers are well-versed in the proper use of the machine placing system (i.e., the clamp, plus all related equipment and vehicles).
• Never stand underneath a loaded clamp.
• Prior to each use, inspect the frictional pads to ensure that they are not worn down and are in good condition.
• Machine efficiency can be significantly increased by proper planning and placement of materials on site?EUR??,,????'??+ plan ahead and save time & money!
• Do not exceed the recommended load specified by the manufacturer.
• Ensure that overall maintenance of the clamp and all machinery is kept up.