Retaining walls are a critical component of landscaping and construction, serving both functional and aesthetic purposes. However, there are eight common retaining wall mistakes that, if not avoided, can significantly diminish the lifespan of your retaining wall and, in some cases, lead to catastrophic failure. The consequences of such failure can range from costly repairs to potential safety hazards.
Whether you’re planning to tackle a retaining wall project yourself or entrust it to a landscape contractor, it’s essential to be well-informed about the potential pitfalls and dangers associated with design and construction practices. In this guide, we’ll walk you through these eight critical mistakes to help you navigate your next retaining wall project with confidence and ensure that your investment stands strong for years to come.
Failing to Use Adequate Drainage
A retaining wall’s functionality will be compromised if the soil that the wall is retaining is not relatively dry. For this to happen, the wall must be built with the proper drainage system to allow the water to drain away.
A proper drainage system consists of several major components, which is dependent on the type of wall that is being built and the surcharge that it will be holding. The three main components of a proper drainage system for retaining walls are drainage rock behind the wall, drainage pipes to allow water to be diverted away from the wall, and Installation techniques that are built for adequate drainage.
You need at least 12 in of drainage rock directly behind the retaining wall. You may need additional drainage rock depending on the height of the wall or your particular climate and in some cases, a drainage pipe will be necessary to divert water from behind the wall
Laying drainage pipes at the correct slope is a fundamental principle in effective drainage system design and installation, especially when it comes to structures like retaining walls. This sloping of drainage pipes is crucial for several reasons:
The primary purpose of drainage pipes is to divert water away from the retaining wall. When these pipes are laid at a slope, it ensures that water flows naturally in the desired direction, preventing it from pooling or collecting around the wall.
Gravity is your ally when it comes to drainage. By sloping the pipes, you’re utilizing gravity’s force to move water efficiently. Water always seeks the lowest point, and a sloped pipe provides that path, guiding water away from the wall without the need for mechanical assistance.
Without proper slope, drainage pipes may not effectively drain water away from the wall, leading to soil saturation. This saturated soil can become heavy and unstable, increasing the risk of wall movement or collapse. A well-sloped drainage system prevents this saturation, keeping the soil in a stable condition.
If water were to accumulate behind a retaining wall without proper drainage, it could create hydrostatic pressure. This pressure can push against the wall, causing structural stress and potentially leading to damage or failure. Sloped drainage pipes help relieve this pressure by swiftly removing excess water.
Effective drainage systems require less maintenance. When water is consistently directed away from the wall, there’s less risk of debris, silt, or sediment accumulating in the pipes, which can hinder their function. A proper slope helps keep the pipes clear and functioning optimally.
To achieve the correct slope for your drainage pipes, it’s important to calculate the gradient based on factors such as the length of the pipe run and the desired drainage rate. This calculation ensures that water moves away from the wall efficiently and without causing issues like standing water or erosion.
It is important to consider your climate as well because freeze-thaw cycles can negatively impact the wall. With the soil expanding and contracting as the water in it freezes and thaws, your wall will experience incredible levels of stress that can lead to failure of the wall. An adequately built drainage system will allow the water to be safely diverted away from the back of the wall.
Choosing the Wrong Material
Substandard materials can leave you with a wall that’s not even worth the cheap materials it was built from. A retaining wall is a big investment so protect your investment by going with quality materials that will last a lifetime.
Poor materials can be in the form of improper aggregates, cheap blocks that are only meant for decorative purposes, and DIY level materials for professional grade projects.
An important thing that I want to mention is, when purchasing your materials, go to a rock yard for your aggregate materials and a retaining wall block dealer for retaining wall blocks. One of the easiest ways to drive up the price of a wall is to use Home Depot and Lowe’s materials that are usually sold at a huge upcharge for the convenience. Also when you go to Home Depot and Lowe’s to purchase materials you miss out on the benefit of speaking to professionals who handle these types of situations every single day.
One poor material that is often used is railroad ties, but these are a poor material for retaining walls that are intended to last a long time. Railroad tie walls often rot over the years and collapse, leaving you with the need of another retaining wall. At this point, some municipalities even banned the use of railroad ties for certain retaining wall situations so be sure to use caution if this is a material that you or your contractor would like to use.
The ideal materials to use are Depending on your location, climate, and budget.
Not Leveling the Courses Properly
This is even more important on the base course (the bottom row) when building the wall. The base course serves as the cornerstone for the entire retaining wall structure. It bears the weight of all the courses stacked above it. Any inaccuracies or deviations in the base course’s level will propagate throughout the wall, potentially leading to tilting, leaning, or even collapse of the wall as subsequent courses are added.
A level base course not only ensures the structural stability of the wall but also contributes significantly to its visual appeal. An uneven or sloping base can result in a wall that appears disjointed and unprofessional. Achieving a level base course is essential for creating a wall that is both strong and visually pleasing. Also a level base ensures that the weight of the wall and the forces acting upon it are evenly distributed. This minimizes the risk of differential settling or shifting of the wall components.
To achieve a level base course, it’s essential to use the right tools and techniques. Here’s how to do it effectively:
- Front-to-Back and Side-to-Side Leveling: As mentioned, each block in the base course should be leveled both from front to back and side to side. This involves adjusting the placement of each block until it is perfectly level in all dimensions.
- Use a Large Level: A large 4ft level, as suggested, is an excellent tool for this task. It provides a broader view and allows for more precise leveling. Placing the level across multiple blocks at once ensures that the entire base course maintains a consistent level.
- Adjust as Necessary: During the leveling process, be prepared to make adjustments by adding or removing base material beneath individual blocks to achieve the desired level. This may require some patience and attention to detail, but it is a critical step in the construction process.
Constructing a Wall That Will Not Support Its Load
When planning to construct a retaining wall that will serve as a foundational support for structures like sheds, driveways, patios, or any substantial load-bearing feature, it’s crucial to communicate this information effectively with your landscape contractor. This communication is a pivotal step in ensuring the success and safety of your project. Here’s why it’s so important:
Different structures impose varying loads or weight distributions on a retaining wall. For instance, supporting a small garden bed is quite different from bearing the weight of a heavy shed or driveway. By informing your landscape contractor about the intended purpose of the wall, they gain a clear understanding of the specific load requirements that the wall must accommodate.
Designing a retaining wall for heavy loads often involves additional reinforcement, such as the use of geogrid, tiebacks, or a stepped design. This extra attention to design details ensures that the wall can withstand the expected stresses and maintain its integrity over time.
The type of material used for the wall can vary based on its intended use. For instance, a retaining wall supporting a patio might require different materials than one supporting a driveway. Knowing the intended load helps in selecting the right materials, whether it’s concrete blocks, timber, reinforced concrete, or other suitable options.
Constructing a retaining wall to support significant weight requires careful planning to ensure its longevity and durability. Properly engineered walls are less prone to settling, tilting, or collapsing, and they can provide reliable support for years to come.
Skipping Engineering and Permits
Engaging with an engineer and obtaining the necessary permits is a critical aspect of building retaining walls, especially when they exceed a certain height. Here’s a deeper exploration of why this is so important:
In many regions, retaining walls that exceed a height of 4 feet trigger the requirement for engineering involvement. This height threshold is not arbitrary; it’s based on safety considerations. Taller walls experience greater forces and stresses, and they need to be designed with meticulous care to ensure their stability over time.
Alongside engineering requirements, retaining walls of certain heights often necessitate permits. These permits are granted after thorough reviews to ensure that the wall meets safety standards and local building codes. Building without the required permits can lead to legal issues, fines, or even having to dismantle the wall if it doesn’t meet code requirements.
Retaining wall engineers are specialists in their field. They have not only the necessary educational background but also years of experience and certifications specific to retaining wall design. Their expertise allows them to tailor the wall’s design to the unique engineering constraints of your site, ensuring both safety and functionality.
Engaging an engineer and obtaining permits before starting the project is not just a matter of compliance; it’s about preventing potential problems. A well-designed and properly permitted retaining wall is less likely to experience issues like settling, tilting, or collapse. It also gives you peace of mind knowing that your wall is built to last.
When working with a landscape contractor, it’s crucial to ensure that they have the proper engineering and permits in place before commencing the project. This not only safeguards the structural integrity of the wall but also holds the contractor accountable for following legal and safety requirements.
In essence, unless your retaining wall is relatively short (below 4 feet) and experiences no additional loads or complex conditions, it’s highly advisable to involve an engineer and secure the required permits. Doing so ensures that your retaining wall is designed and built to meet safety standards, local regulations, and the specific needs of your site, ultimately preventing potential problems and costly issues down the road.
Improperly Using Geogrid
Geogrid is a crucial component in the construction of retaining walls, especially when dealing with larger and more complex structures. Its role in reinforcing the soil mass cannot be overstated, and understanding how to use it correctly is essential for the wall’s stability and longevity. Here’s a detailed explanation:
Geogrid is a specialized, high-strength material that is used to reinforce the soil or fill behind a retaining wall. Its primary purpose is to enhance the soil’s load-bearing capacity, allowing it to withstand much larger loads than it would without reinforcement. This is especially critical for retaining walls that are taller than 4 feet, as they need additional support to prevent failure.
Geogrid becomes essential in several specific scenarios:
- Taller Walls: Retaining walls exceeding 4 feet in height require geogrid reinforcement due to the increased gravitational forces acting on them.
- Surcharge Loads: If the wall experiences surcharge loads, such as those from buildings, cars, or other heavy structures, geogrid helps distribute these loads effectively.
- Slope Pressure: Walls that face the force of an uphill slope need geogrid to counteract the lateral pressure exerted by the soil mass.
It’s crucial to differentiate between landscape fabric and geogrid. Landscape fabric, while it may look similar, is not a suitable substitute. Landscape fabric has small pores that can become clogged with soil particles, preventing water from passing through. This leads to hydrostatic pressure buildup, which can compromise the wall’s stability. Geogrid, on the other hand, has larger holes and spacing that allow both water and soil to pass through while maintaining its structural integrity.
Geogrid should always be placed horizontally across the wall, not vertically. Horizontal placement maximizes its ability to distribute loads evenly, reinforcing the entire width of the wall. This ensures that the wall can withstand both the lateral and vertical forces it encounters.
A general guideline is to have one foot of geogrid placed horizontally for every 2 feet in wall height. To increase the strength of the geogrid, it’s more effective to extend its length than to add extra layers. Longer geogrid provides better lateral support and allows the wall to hold a greater mass.
Not Following Manufacturer Instructions
When constructing retaining walls, the choice of building material is a pivotal decision, and the type of blocks you select can significantly impact the success and durability of your project. Concrete Masonry Units (CMUs) offer a standardized building material with consistent characteristics, making them a popular choice. However, it’s crucial to recognize that different manufacturers produce various types of retaining wall blocks, and each may have its unique assembly requirements. Let’s delve deeper into these considerations:
CMUs, also known as concrete blocks or cinder blocks, provide the advantage of standardized dimensions and composition. This uniformity makes them relatively predictable and straightforward to work with. Manufacturer instructions for CMUs are typically clear and easy to follow, which simplifies the construction process.
Retaining wall blocks, on the other hand, can vary significantly between manufacturers. Each manufacturer may employ distinct systems for constructing their walls. This means that you cannot assume that two wall blocks from different manufacturers are used in the same way. Understanding the specific requirements for the blocks you’ve chosen is crucial to ensure the wall’s stability.
Different types of retaining wall blocks may require various assembly methods. For instance:
- Some blocks need to be filled with gravel: This filling enhances the wall’s strength and stability, providing additional support beyond the blocks themselves.
- Some use a rod system: These systems involve inserting rods or pins through the blocks to secure them together, adding to their structural integrity.
- Some rely on interlock and weight: Certain blocks depend on the interlocking design and the sheer weight of the blocks to hold the wall upright.
When working with hollow blocks, it’s often necessary to core fill them with an aggregate material like gravel or crushed stone. This core filling is a critical step as it reinforces the blocks and provides essential strength to the wall. Failure to core fill can leave the wall reliant solely on the lip on the back of the retaining wall block, which may not be sufficient for long-term stability.
The choice of retaining wall block should align with the specific requirements of your project. Some blocks are primarily decorative and suitable for smaller projects, while others are engineered for massive retaining walls capable of holding substantial loads. Consulting manufacturer instructions and seeking guidance from local dealers is essential for making an informed choice.
Trying to Bite Off More Than You Can Chew
Building a retaining wall can indeed be a DIY project, but the feasibility of doing it yourself depends on several factors, including the scope of the project, the type of wall you’re constructing, and your experience with the necessary tools and equipment. Here’s a closer look at these considerations:
The size and complexity of the retaining wall project are crucial factors in determining whether you should tackle it yourself or hire professionals. For smaller, straightforward walls in your garden or landscaping, a DIY approach can be a rewarding and cost-effective choice. However, when dealing with larger walls, engineered designs, terraced walls, walls on slopes, or any project that demands structural expertise, it’s usually best to entrust the work to experienced professionals. These projects require a higher level of technical skill and knowledge to ensure safety and long-term stability.
Building a retaining wall can be physically demanding, especially for larger projects. It often involves significant excavation, lifting heavy materials, and precise construction work. If you attempt to take on a labor-intensive project by yourself without adequate help, you risk not only physical strain but also compromising the quality of the wall. In some cases, larger projects may require the assistance of three to five adults working over several days to complete the job effectively.
Constructing a retaining wall often involves the use of various tools and equipment, including excavators, skid steers, plate compactors, and more. Before embarking on such a project, it’s imperative that you possess the necessary skills and knowledge to operate these tools safely and effectively. Inadequate equipment handling can lead to accidents, project delays, and compromised results.
Engaging a reputable landscape contractor with experience in retaining wall construction offers several advantages. Professionals bring expertise in wall design, engineering, and construction techniques, ensuring that the wall meets safety standards and local regulations. They also have access to specialized equipment and materials, which can streamline the project and enhance its quality.
Collaboration with a skilled landscape contractor allows you to transform your vision into reality. Professionals can work with you to design and build the retaining wall of your dreams, creating an attractive and functional addition to your landscape. They also have access to a wide range of materials and design options, ensuring that the final result complements your home’s aesthetics and enhances your outdoor space.
While DIY projects can be rewarding, it’s essential to recognize your limitations and prioritize safety and quality. For larger, more complex, or engineered retaining walls, seeking the expertise of a landscape contractor is often the wisest choice, ensuring that you achieve the desired results while avoiding potential pitfalls and challenges.
In summary, understanding and avoiding these eight common mistakes in retaining wall design and construction is essential for the long-term success of your project. A failing retaining wall can have severe financial consequences and pose safety risks, making it crucial to prioritize proper planning, materials, and construction techniques.
Whether you choose to embark on a DIY project or enlist the expertise of a professional landscape contractor, being aware of potential pitfalls and safety concerns is paramount. By following best practices and adhering to industry standards, you can ensure that your retaining wall not only stands the test of time but also enhances the beauty and functionality of your outdoor space.
Retaining walls play a vital role in shaping and safeguarding your landscape. Avoiding these mistakes ensures that your investment in a retaining wall provides lasting value, protects your property, and contributes to the creation of a secure and visually appealing environment.