Some retaining wall projects involve forces and site conditions that a standard gravity wall cannot safely manage on its own. Taller walls are an obvious example, but height is only one factor. Steep slopes, unstable soil, significant water pressure, failed existing walls, and loads above or behind the wall can all increase the structural demands placed on it.

Rolling Hills Landscapes builds engineered retaining walls for homeowners throughout Greater Pittsburgh. These reinforced wall systems use project-specific engineering to determine how the wall should be constructed for the conditions of the property.

When Does a Retaining Wall Need to Be Engineered?

The need for engineering depends on the combination of wall height, slope, soil conditions, drainage, wall location, and nearby loads.

A steep slope can increase the forces acting on a wall, while poor or unstable soils can affect both its foundation and the retained area. Water also needs to be considered because excessive pressure behind the wall can affect structural performance.

Driveways, pools, patios, homes, and other structures above or near a wall can introduce additional loads that need to be accounted for in the design. Terraced properties may require additional analysis because walls positioned close together can influence one another.

Failed existing walls also need careful evaluation. Rather than simply rebuilding the same structure, the cause of movement, leaning, cracking, or failure should be identified so those conditions can be addressed in the replacement design.

"Every retaining wall over four feet tall requires engineering and a permit. This is true of every township in Pennsylvania, it's a state law, not a municipal restriction. You cannot get around it by building two three-foot walls instead of one six-foot wall. These aren't my opinions. They're the law."

John Linder, Owner & Lead Installer

Engineering, Permits and Approvals

The process begins with evaluating the proposed wall location and height, existing and proposed grades, slopes, soil conditions, drainage, and loads from nearby features. This information provides the basis for determining the structural requirements of the project.

A civil engineer performs the necessary calculations and develops the structural design, including reinforcement specifications and stamped drawings. Where required, those plans are used for permitting and inspections during construction.

Rolling Hills Landscapes coordinates this process and builds the retaining wall according to the approved plan. The civil engineer is responsible for the structural design, while our team follows the specified dimensions, materials, reinforcement, drainage, and construction requirements in the field.

Reinforcement, Backfill and Drainage

One of the primary differences between a standard gravity wall and many engineered retaining walls is reinforcement. Geogrid can be incorporated into the retained soil to create a reinforced mass behind the wall and help the system manage greater structural demands.

The engineered design specifies the required geogrid length and the intervals at which reinforcement must be installed. Direction is critical because many geogrid products have a primary strength direction and must be oriented correctly. Layers also need to be placed at the specified elevations, properly separated rather than incorrectly overlapped, and pulled taut as backfill is installed.

Backfill selection and compaction are equally important. The specified material is placed in controlled layers and progressively compacted with appropriate equipment. Poor material selection or inadequate compaction can contribute to settlement and movement within the completed wall system.

Drainage is also incorporated to prevent excessive water pressure from developing behind the wall. Drainage stone, grading, and other water-management components are installed according to the requirements of the project.

These components need to be installed according to the engineered design rather than improvised during construction.

"I have seen these walls fail time and time again. In fact, I was 30 seconds away from having a wall collapse on me. It was a neighbor's 6 foot tall wall that landed where I was cutting grass 30 seconds prior. Dirt collapses at 45 miles per hour, and retaining walls seldom give warning of impending catastrophic failure. Proper installation methods are critical, no matter the size or scope of a retaining wall project."

John Linder, Owner & Lead Installer

Standard vs. Engineered Retaining Walls

Not every residential grade change requires an engineered wall. Smaller and less complex projects may be appropriate for a standard gravity retaining wall. Read More About Retaining Walls >>

If you are unsure which approach applies to your property, read our Retaining Walls vs. Engineered Walls comparison >> for more information about the differences between the two.

Have a Challenging Retaining Wall Project?

If your property has a tall wall, steep slope, failed existing wall, difficult soil, drainage concerns, or significant loads near the proposed wall, Rolling Hills Landscapes can evaluate the site and determine the appropriate next steps.

Contact us today at 412-885-7049 or through our online form to schedule a site assessment for your engineered retaining wall project.