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Retaining Walls

Today's homeowners are always looking for ways to increase the value of their property. One of the first things people do to increase value is to improve the overall appearance of the home by enhancing its curb appeal with landscaping. The popularity of adding a retaining wall has increased significantly because of the flexibility of design, practical uses and aesthetic options such as shape and color of the blocks.




There are two types of retaining walls: gravity walls and reinforced walls. A gravity wall, or non-reinforced wall, relies on the weight and batter of the retaining wall to resist the loads imposed on the structure by the retaining soil and is usually less than four feet in height. A reinforced wall is designed by a qualified engineer using geosynthetic reinforcement. Reinforced walls are usually greater than four feet tall and have special loading conditions present like slopes or surcharges.

While adding to the look of a landscape, a segmental retaining wall (SRW) can also serve a practical purpose. One of the major uses for SRWs is to help control erosion. For example, steep hills can lead to mudslides, improper drainage and general unsavory appearance of the property. Such was the issue facing upscale homeowners in Deephaven, Minn., who needed to replace a boulder-laden, steep hillside. They wanted a practical wall that was aesthetically pleasing while allowing for decorative options. For a solution, they turned to a local contractor and Anchor Wall Systems.

A curvaceous, tiered retaining wall was suggested to best spruce up the yard. Overall, the entire wall would stand 11 feet tall. The design of the wall would encompass four interconnected levels, each terrace measuring 3.5 feet tall.

With the design and layout of the wall finalized, the homeowners elected to use Anchor Highland Stone¨ and new jumper accessory unit. Highland Stone is a three-piece concrete retaining wall system featuring a face texture that replicates natural stone. The jumper unit is an accessory that has the same color and texture of the other blocks, but it stands vertical in the wall. This breaks the pattern of all horizontal blocks across a typical retaining wall providing the freedom to experiment with different pre-arranged patterns in a wall, or choose random placement for a more customized look.

The project began with major excavation — the landscapers took out 75 to 80 yards of soil and two to three large trees. Once a base had been established, the set-back of the block caused the radius of each course to gradually increase (inside curve)/decrease (outside curve) and eventually affected the running bond of the wall. To maintain proper running bond, partial units were inserted as needed.

   

The result was a whole new look for the property: a retaining wall, curved with a natural stone look, terraces for plants and flowers, and vertical blocks to vary the look, all while effectively channeling the water run-off from the steep hillside.

Before building your retaining wall project, Anchor Wall recommends key steps to take into consideration in planning, on-site evaluation and installation.

Planning
The first step in building a retaining wall is thorough planning. A site plan, design soils information and a wall construction plan are essential before getting started on a retaining wall project.


The site plan is a detailed drawing of the site including wall location, length, elevations, information on grading, underground utilities, erosion control and storm water management.




The design soils information identifies the kinds of soils on your construction specifications.


The wall construction plan is a blueprint of the wall you're going to build, and has five requirements: wall, toe and crest elevations; reinforcement location and length; soil conditions and parameters; drainage and other wall details; and wall construction specifications.

When creating a wall construction plan, it is important to consult with an engineer, as it is their job to determine the length and the number of geosynthetic reinforcement material that is required to stabilize a site-specific segmental retaining wall system, as well as provide drawings that show how a wall should be constructed. Geosynthetic reinforcement is a sheet material made from high-tensile strength polypropylene, polyethylene or polyester that, when used properly, helps to support the retaining wall system.

The need for geosynthetic reinforcement depends upon many factors, including wall height, soil conditions, expected loads and earth movement. To determine whether geosynthetic reinforcement is warranted, an engineer should evaluate every retaining wall project, even those lower than four feet. When geosynthetic reinforcement is required, an engineer can specify the appropriate materials, number of layers and correct placement of geosynthetic reinforcement based on the particular site conditions and your project design.

On-site Evaluation
   

When all plans for the project are in place, the next step is to conduct an on-site evaluation — both for materials and for safety.


To protect materials from surrounding equipment and construction, lay out a storage area for the block, reinforcement, drainage and base materials. Check the delivered materials carefully. Elevate the blocks on wooden pallets, and keep the reinforcement dry, covered and clean.


Follow the guidelines for worker and job site safety established by your state's Department of Labor. And take special precautions for OSHA requirements, which include maintaining safe slopes. Coordinate with the foreman to make sure you know the location of underground utilities.


Technology and innovation will undoubtedly continue to fuel and expand the SRW construction market. For example, there is now a special process called global stability analysis that can analyze the projected stability of a wall before it is built by determining how the wall will react to earth pressures. In the meantime, Anchor Wall Systems has professional engineers on staff to answer your questions with preliminary designs using Anchor's comprehensive software program, Anchor Wall Design 4.0.

Installation Tips


Using a shovel or a skid loader, dig a trench about 24 inches wide and deep enough to fit the required amount of buried block and compacted base. For walls four feet high and shorter, bury one course of units. Total wall height includes the height of any buried courses.


Firmly compact the soil in the bottom of the trench. Lay six inches of compactable base (e.g., sand and gravel) in the bottom of the trench and compact.


Place the first layer of Anchor units without lips on the prepared base (lips must be manually knocked off units before placement). Position the units side-by-side, in full contact with the base, and level in both directions using your carpenter's level. Backfill with free-draining aggregate.


Anchor recommends using 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.


Continue assembling additional courses in a running bond pattern, pulling each unit forward until secure. Use free-draining aggregate to backfill each additional course as it is installed.


Place drain tile behind the wall at grade to allow water to drain from the backfill (organic or clay-type soils are not recommended). Outlet the drain tile through the wall at every low point, or every 75 feet of wall length and around the ends of the wall. Backfill with free-draining gravel 12 inches behind the wall, in six-inch layers.


Fill any remaining areas behind the wall with soil. Compact every 12 inches. Repeat steps five through seven until the wall reaches the desired height.


Firmly compact native soil every 12 inches behind the wall. Do not compact directly on top of the units.







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