This article provides a broad-based overview of some options available for implementing erosion control to an unrestrained slope by using change of grade structures, more commonly referred to as retaining walls.
Gravity and Segmental Retaining Walls
One option involves building what is known as a gravity wall. A gravity wall is defined as any wall where adequate mass is incorporated into the construction to resist forces exerted on the slope to prevent movement or sliding. A gravity wall can be as simple as a small boulder wall, or it can consist of larger “big block” units, such as Redi-Rock, in which the sheer mass and size of the wall system contains the soil mass. These walls commonly are used where it is not feasible to utilize such reinforcing components as geogrids, geotextiles, metal straps or mesh, soil nails, or other products. In these cases, such circumstances as property lines, rights of way, or utility easements typically restrict the use of a “reinforced” retaining wall.
Segmental retaining walls (SRWs) are among the most commonly used reinforced retaining wall systems. These products originally were developed in the early 1980s, and, according to the National Concrete Masonry Association (NCMA), 300 million square feet of dry-cast SRWs were produced for the commercial and “do it yourselfer” market in the US in 2009. These products, sometimes referred to as modular systems, vary in appearance and adapt very well to many different situations. Many times, specific product brands, such as RidgeRock or Keystone, are specified in a plan, but most brands are very comparable and utilize similar design parameters and engineering. In the US, some of these walls have been constructed to a height of more than 70 feet, and their acceptance is almost universal within the construction industry.
There are situations in which an SRW is not the most effective application. These circumstances typically arise when the soils to be retained or reinforced are not suitable for this type of solution, or when proper reinforcement cannot be installed due to space restrictions. Mechanically stabilized earth (MSE) walls are accepted within the construction industry as well. This type of wall particularly is desirable when water must migrate through the wall face. TerraWall by Maccaferri is a good example of an MSE wall that utilizes a metal reinforcement alternative in dealing with erosion control.
Tips For Success
Keeping a few things in mind will ensure successful implementation of retaining walls as a strategy for erosion control. Always insist that an engineer licensed in the state where the wall is to be constructed examines the site and designs the walls. Next, make sure that the installer and the sales person(s) representing the products are both knowledgeable and experienced. Visit the project site, and work onsite with the installers. Oversight is especially important when there is a new or less-experienced installer on the job site, or the installer’s past experiences don’t include the specific installation required on the site. And remember: There are a variety of retaining walls from which to select, and the assistance of a knowledgeable product representative, a licensed engineer, and a competent and experienced installer are imperative for a successful solution.
