Retaining Wall Design
Imagine if the world we lived in was nothing but flat? Pretty boring, right? Luckily for us, we live in rich landscapes with a diversity of elevation, soil cover, and shape. However, sometimes this same diversity can be an issue for structural integrity- and that’s where retaining walls come into the picture.
Retaining walls allow us to stabilize and ‘hold back’ soil that can otherwise slip and erode, strengthen the landscape for buildings, roadways, and other structures, and ensure that we have beautiful properties.
This means they allow us to make better use of every lot, protect property and life from unstable natural landscape areas, and add beauty to lot designs.
Why to Use a Retaining Wall: Dealing with Soil
Retaining wall designs are created by engineers to support soil laterally in sloping landscapes, and must resist the lateral pressure of soil to avoid collapse. Soil can be remarkably heavy, and can exert different forces due to expansion and contraction during icy weather, when water present in the soil, and sometimes due to changes made to the landscape for buildings, foundations, or traffic. All of these factors must be considered when designing a retaining wall.
Because of the vagaries of soil movement, your lot can look great, but be at considerable risk from slipping or falling earth, depending on the inherent and weather-related soil properties. This movement can also put buildings in peril, as well as endanger users. However, a well-designed retaining wall should insure an effective wall to last for many years.
Retaining walls act to provide a ‘shelf’ that prevents soil movement and erosion, and they also help better distribute soil weight, improve graded landscapes, and keep your commercial landscape safer and more stable. Plus, they make a fantastic decorative feature when used correctly!
Retaining wall design is not one-and-done, however. A retaining wall design that’s right for your needs is heavily dependent upon the weight that is put upon it. The majority of this force is caused by the soil and aspects acting on it. Xpress Engineering’s skilled structural engineers create appropriate retaining walls after calculating the soil burden the retaining wall must be able to hold.
The soil burden is based on four different factors: (a) the strength parameters of the soil, (b) the unit weight of the soil, (c) the type and amount of wall movement, and (d) the drainage conditions of the backfill material used. A proper retaining wall design considers and accounts for all of these factors and conditions to insure that your wall can do it’s job for many years to come.
Retaining Wall Design Engineering: the First Step
So, determining which forces(s) are involved in the design is one of the first steps in the creation of any retaining wall structure. In fact, it’s critical to solid retaining wall construction.
The answers science gives us here will determine how many retaining walls will be needed, their depth/height and design, and the materials used in their construction.
While we won’t go in-depth into the mechanics, here are some key points that will be considered:
- If the wall is successfully restrained from moving, the lateral pressure is called at-rest, or lateral pressure
- Due to the soil pushing on the wall, it may deflect or tilt outward. With sufficient tilt outward, a triangular ‘failure wedge’ will be created. This type of pressure is called active earth force.
- In certain situations, the wall may be pushed back into the soil it is retaining. The pressure for this condition is passive earth force.
Together, these create different scenarios, and need the design of the retaining wall to shift to match (and counter) them. Another key element is bearing pressure, which simply expresses the load carried over a specific area.
Ideally, your retained soil exerts less force on the walls than the ‘push-back’ from the engineered strength and design of the retaining wall project, holding everything in place effortlessly.
As you can see, this gets quite complex- but that’s why you can trust the experts to do this work for you. We will then advise on the best type of retaining wall design, as well as the best materials, for what you need.
Designing Retaining Walls: Thinking Beyond Lateral Earth Pressure
There are a variety of types of retaining walls, each with special landscape uses and a ‘maximum load’ they can hold back.
The typical design from Xpress Engineering is a Cantilever Wall, but other types are: Gravity Retaining Walls, Semi-gravity Retaining Walls, or Counterfort Retaining Walls.
Cantilever Retaining Walls are typically the most economical design up to a height of approximately 24 feet and can be incredibly strong when concrete and steel are added to the mix.
The wall design consists of two phases. Firstly, once the lateral force type and magnitude are known, the wall is engineered for overall stability. The wall is investigated for sliding, overturning, and soil bearing capacity failures. Secondly, each element of the wall is checked for strength, and the steel reinforcement is sized accordingly.
Creating a Cantilever Retaining Wall
A typical retaining wall uses 4 key construction areas, all of which are a vital part of the overall structure:
- The Stem: This is the vertical part of the wall, which holds backfill and steadies the wall. Stem thickness is a critical part of the overall wall design.
- The Toe: This is the part of the wall at the base on the front.
- The Heel: This is the retaining wall footing behind the wall on the 'filled' side
- The Shear Key: This projects down under the wall footing and can be up to one third of the overall wall height, even though you will never see it beneath the soil of the finished wall.
These key parts of the wall structure work together to offset the forces active on the wall and behind the wall. They each help to determine the maximum wall height you can install with the materials you choose.
Retaining Wall Design Types
There are a variety of different types of retaining walls. The design from Xpress Engineering is a Cantilever Retaining Wall, but other types include: Gravity Retaining Walls, Semigravity Retaining Walls, or Counterfort Retaining Walls. Cantilever Retaining Walls have been found to be the most economical designs up to a height of approximately 24 feet.
Once the recommended retaining wall design parameters are known and the overall structural design is created, it’s time to choose the right material for the wall.
Strength and capability have a role to play here, and so does simple aesthetics. Here are some common retaining wall designs that work with our designs:
Poured Concrete Retaining Wall Designs
Poured concrete retaining wall designs, sometimes just called ‘poured’ retaining walls or ‘concrete’ retaining walls, combine strength and dexterity, and allow for precision construction in any space.
In fact, concrete is one of the best retaining wall materials, although it can come at a higher price. They are quite technical to create, too, but this also means they can be used for almost any space and design.
With modern concrete technology, we can also add texture and color, embed decorative or strengthening objects, and much more, ensuring the end result is as pleasing as it is stable.
This are one of the most versatile and customizable types of retaining wall in use today, well suited to the overall shape of cantilever walls, and have a great safety factor, but they need a solid grasp of design and engineering to create successfully.
Steel reinforcement is often used in larger wall designs, allowing for stronger footing in the soil and for the wall to carry a higher minimum-maximum force without wall failures.
Block Retaining Wall Designs
Block retaining walls are, as the name suggests, created with blocks (aka “cinder blocks” or “concrete blocks”) instead of poured concrete. It’s the oldest type of design for retaining walls, and technically covers anything from brick walls upward. Most modern designs use larger poured concrete blocks for better aesthetics, and to allow them to be built to a larger size.
However, past a certain height wall failures can occur, as there are more ‘moving parts’ in the design which can be acted on by soil force and weight, and hydrostatic pressure.
This means they have specific uses and designs, and this needs to be correctly determined in conjunction with the retaining soil, backfill soils and drainage, earth pressures, and necessary wall height.
They are great for already bound soils, which means they work fantastically in garden bed designs on a slope.
They’re often spaced at regular intervals over a landscape, allowing the construction of the slope to ‘step down’ in a stable and aesthetically pleasing way while providing plenty of support, and can be steel-reinforced if necessary for overall structural stability, too.
Pressure Treated Wood Retaining Wall Designs
Again, the design of retaining walls is only half the journey. The materials used must be able to support the minimum required force of the soil acting on them without sliding or pushing the footing of the wall out of place, which would lead to structural failure.
Treated wood is stronger than ‘normal’ wood, but still has its limits. This is a design suited to lower wall heights, and any structures designed with pressure treated wood must take these materials into account.
Remember that any wood will rot over time, too, so it has a much shorter lifespan than concrete and steel walls. They’re often used to bring stability to a landscape, rather than hold space for building construction or tame higher grades.
This are one of the most versatile and customizable types of retaining wall in use today, well suited to the overall shape of cantilever walls, and have a great safety factor, but they need a solid grasp of design and engineering to create successfully.
Steel reinforcement is often used in larger wall designs, allowing for stronger footing in the soil and for the wall to carry a higher minimum-maximum force without wall failures.
Retaining Wall Installation
Once you’ve ordered your Xpress Engineering retaining wall design, and you’re confident it’s what you want, it’s time to get it installed!
Whether you hire a contractor or decide to tackle the project yourself, the site will need a certain amount of preparation. You or your contractor may need to regrade the location for your wall, and move soil around to create a better, more stable platform for construction of your new retaining wall.
Your Xpress Engineering design will detail all of the critical aspects of the project, so you and/or your contractor will have a very good basis for the work before the installation goes forward. You can be confident that you have a professional design to insure a successful (and legal) plan for your new retaining wall. Rest assured, the final product will be well worth it!
Retaining Wall Design FAQs
Yes! You may be able to perform the work yourself, but guessing on material size, type, and spacing is a recipe for disaster. More than likely, you will have to replace the wall again in a few years due to failure if you do not have it properly designed.
Prices vary nationwide, but a typical retaining wall design with calculations and a Professional Engineering stamp will cost between $1000-$2000.
If you contract with a local engineering firm, you could be looking at as much as two months before you are able to receive your design. Our staff of engineers are focused on retaining wall designs all day and can produce a set of drawings and calculations in 24 hours (with the expedited fee option.)
Besides having the best turn-a-round timeframe for a retaining wall design, Xpress Engineering specializes in retaining wall designs! It is similar to having a pain in your elbow and visiting your general practitioner doctor. He may know how to provide you pain medication so you feel better, but the best person to address your issue would be a joint specialist who deals with this all day long, every day!
A significant factor in retaining wall failures occur due to original design and construction. Many walls were done by home owners or contractors that thought they knew best, but in reality were under-sizing different elements of the wall which leads to premature failure. Water is also a big cause of retaining wall failures. Explore Xpress Engineering for a more thorough explanation of how water can cause a failure.
Most building jurisdictions allow a home owner to perform work on their own property without having a contractor license. Permits may still be required and you must check with the building department before construction. If you are hired to build a retaining wall on someone else’s property, you must have a contractor license.
Yes! You will receive all the needed information and drawings to properly build a safe and long-lasting retaining wall. It is recommended to still consult with a contractor to make sure proper steps are taken in the construction. You can always reach out to Xpress Engineering with any design related questions as well! We are here to help!
Sometimes during the design phase of a larger construction project, it is not known that a retaining wall is needed until the project starts. In this situation, the project could be put on hold by the building department until the contractor submits a retaining wall design. To avoid any costly delays on the project, Xpress Engineering has the option for an expedited design of a retaining wall. We are the only company in the United States offering this service.
We are here to help! Send us an email or visit the FAQ page to see if others have had the same question!
The size of all the elements of a retaining wall are critical for the structural stability of the wall. It is critical that the wall be designed by a professional to avoid costly errors or failure. Xpress Engineering provides these designs, custom for your location/situation.
You may need to obtain both planning approval and/or a permit. Many HOA’s will require approval as well. Some building departments do not require a wall taller than 4ft unless it is adjacent to a driveway. Always check with your local building department before starting.
There are many different materials that can be used and they vary in pricing, look, and capabilities. Xpress Engineering can design multiple different types of retaining walls. Concrete masonry block (CMU), cast-in-place concrete, wood posts and boards, heavy stone, are just a few examples. Refer to the Retaining Wall Order page for a few pros and cons for each type of wall material.
This can vary significantly across the United States and depending on the wall type and even the contractor selected. Stacked block or wood retaining walls can be the most affordable for shorter height walls, although they can be comparable in cost to other CMU and concrete walls at taller heights.
You can email Xpress Engineering or fill out a request form and will receive a free “Guide to Retaining Walls”. We are here to help!
Click here to answer a few easy to answer questions! Once you submit your design answers and purchase the wall, you will receive a confirmation email. The criteria for your wall will be placed in the queue of one of our engineers who will perform the design. If they have any additional questions, they will reach out to you! It’s that easy!
Not ready to order today? Just bookmark this site and when you’re ready to order, we’ll be here to help!
We Provide Professionally Engineered Retaining Wall Designs in 24-Hours
Xpress Engineering will have the design, calculations, and specifications for the project in your inbox within 24-hours of your query (M-F) in nearly every cases, so you can get your retaining wall project started very quickly.
Is Xpress Engineering able to design what you need? Following are factors that could complicate or delay your design:
- You have been provided a Geo-technical (Soils) Report for your specific project.
- You can see significant cracking or previous movement in slabs and/or foundations close to where the wall is to be installed.
- You need a wall over 8 feet tall.
- You will be supporting a building structure on top of the retaining wall.
- You will be building the wall very close to a building.
- You will be building this wall parallel and adjacent to a public roadway or highway.
- This is the first retaining wall you or your contractor has ever built
Don’t worry if any of these factors do apply, however! While we may not be able to get you a standard design within 24-hours (M-F), we can very likely still help you create the perfect retaining wall for your needs.
Contact our helpful team at info@xpressenginering.com, and let us know what the complicating factors are. You can feel confident that we can help.
If none of the above conditions are applicable, let’s get started with your retaining wall design!
