How Thick Should a Concrete Retaining Wall Be?
Thickness of a retaining wall depends entirely on the planned purpose and location of your retaining wall. The idea is to create a wall with sufficient wall thickness to tolerate the allowable soil bearing pressure behind it, without the retaining wall design being too thick, which wastes money and time.
The proper portioning of a concrete retaining wall is as important as the overall structural design. Soil type, backslope, hydrostatic pressure, surcharges, and a lot more all affect the answer. Typically, the top of the stem will be no less than 6″ thick, but a lot depends on the earth pressure, vertical load, and other key design elements. As a general rule of thumb, the stem thickness in a cantilever retaining wall is typically about 10% of the wall height. This is a general rule of thumb, but our expert engineers at Xpress Engineering will determine the exact required thickness for your wall.
How Do You Size Concrete Retaining Wall Footings?
A general rule of thumb is the footing width should be 50-70% of the wall height, and the footing thickness ranges from 12” up to 18” for walls over 10 feet in height. Similar to the stem thickness, many factors play into the footing size and site specific parameters will always need to be examined.
If the wall will need extra sliding resistance, a footing key can be used in the concrete wall design. An extension of the stem, it extends below the bottom of the base. Reinforced concrete, with steel built-in for greater integrity, can also be used (mentioned previously in this post).
However, smart retaining wall construction starts with the proper placement of all features. A poorly-designed wall that doesn’t match the soil parameters will fail no matter how thick it is.
How Do You Design a Retaining Wall?
Getting the right design for your retaining wall is critical. Luckily, it’s not a decision you have to make – your Xpress Engineering structural engineer will create an ideal design for your retaining wall with minimum intrusion into your landscape, while still having the depth and loading forces to get the job done.
Firstly, however, we would recommend hiring a licensed contractor to help your survey the entire area of where the wall will go. Planning is a critical first step for all successful projects. However, here’s a few of the steps described briefly which can be discussed with your contractor:
When you design retaining walls, a lot hinges on choosing the right location in the first place. The idea is to create an optimal drainage pattern and grading on the site, considering the existing features of the landscape and foundation soil. The location should also make for minimized excavation and backfill material needs.
Clever Design Parameters
Now gathering the retaining wall site parameters begins. You and your contractor will need to determine the ideal wall height (at the tallest point), with reference to the top of supporting slopes above and behind the wall. Our engineers at Xpress Engineering will need to know if there are other surrounding features that would affect the design, such as, roadways, water ponding, building structures, rock outcroppings, etc. These parameters are critical in the design of the wall to prevent sliding and overturning.
Keep in mind the appropriate building setback for the wall need to be considered and will play an important role in the design. Consult with your local building department to determine your specific property setbacks.
Matching Structural Requirements
Once the parameters are provided, one of our expert engineers will determine the retaining wall thickness, required reinforcement of the wall and footing, necessity of a shear key and more, including any special site specific notes to successfully construct the wall. These wall elements are all based on the parameters provided. We will also provide drainage recommendations, but the final drainage design is completed by your contractor who is more familiar with the seasonal rain that occurs at the project drainage. This is discussed more below. Simply, you won’t have to worry about the retaining structure with our retaining wall designs.
Retaining walls help to stabilize the landscape, but a landscape acts very differently- and has different soil parameters- when it’s wet vs dry. All good wall designs incorporate drainage, typically through the backfill placement, depth, and structural design. Sometimes, greater drainage options, or full systems, will be built in to the space behind the back face of the concrete. Due to the varying locations and geographical climates, the final drainage pipe sizing, depth, amount, and type will be done by your contractor. Xpress Engineering recommends hiring a local Civil Engineer who can determine water shed and/or ground water demands and size the drainage accordingly.
The total wall setback, thickness, length, footing size, and design of retaining walls is an art, but done correctly by a structural engineer, your retaining wall will last for decades to come.
Are you ready to get started? Contact Xpress Engineering today, and we’ll have our team get right back to you with the perfect concrete retaining walls for your needs.