Concrete Block Retaining Walls
Concrete block retaining walls are among the most popular types of retaining walls. Retaining walls are typically built to manage sloped properties and can be used to create or add to a flat usable space for the property owner.
This additional space could be used to build a patio, garden, parking, or even an extra bathroom! Retaining walls can also be built to include other useful features such as stairs, planters or benches.
How does a concrete block retaining wall work?
Like all retaining walls, concrete block retaining walls are constructed to level out sloped properties and create useful spaces in your yard or landscape. The main purpose of the retaining wall is to keep the soil at different levels on either side of the wall. By flattening slopes the walls help to prevent soil erosion and other property damage. Retaining walls also can create texture and interest in a garden and they’re sometimes used to change levels or build raised gardens.
All retaining walls must be strong and durable. They must have the capacity to hold back the weight of the retained soil and resist the forces present in the environment and the surrounding earth. Block retaining walls are often an excellent choice.
Concrete Block Types Used for Retaining Walls
Retaining wall blocks, often made of concrete, offer strength and durability, along with speedy assembly. Retaining wall blocks stack up neatly, sometimes with interlocking edges, and may allow for fastening with pins or clips. They have consistent and even sizing, helping them look professional and well-built. Plus, they come in a wide range of shapes, textures and colors to support various designs.
These versatile blocks are an excellent choice for retaining walls in nearly any setting. However, the best choices will normally be hollow to allow for strengthening necessary for most retaining walls.
What Are Concrete Blocks?
Concrete blocks are comprised of water, cement, and aggregate loads, such as sand, gravel, or crushed stone, while cinder blocks (sometimes called “concrete blocks”) contain coal ash.
Remember: the main difference between concrete and cinder is their aggregate load. Cinder blocks include with coal cinder (ash), generally to reduce weight, while solid concrete blocks are filled with sand, gravel, or crushed stone. In either case, mixed and cured, these ingredients form a hard, strong, and durable substance, perfect for construction.
Concrete Blocks (or CMU’s) for Retaining Walls
Concrete blocks used for retaining walls are often referred to as CMU’s. They may be available in various shapes and sizes, but are hollow when described as CMUs (Concrete Masonry Units), allowing for added strength by filling the void spaces with mortar and/or rebar.
Solid concrete blocks are often called concrete bricks. However, some types of solid concrete blocks can bring different advantages or disadvantages to a project.
Hollow Concrete Blocks or CMU’s
Hollow concrete blocks (aka CMU’s) are the most common type of block used for retaining walls, and are the type specified for Xpress Engineering block retaining wall designs. Hollow concrete blocks generally include relatively light aggregates.
Typically, hollow concrete blocks have large voids. The solid area should be equal or greater than the hollow area for a hollow concrete block to reach its maximum load capacity.
There are two types of hollow concrete blocks: load-bearing hollow concrete blocks and non-load bearing hollow concrete blocks. With load-bearing blocks, professional builders typically fill the voids with mortar for increased strength and resistance.
Concrete bricks are rectangular blocks made of concrete. While some manufacturers use solid concrete to create a stronger structure, others juggle the ingredients for economic purposes.
Concrete bricks can provide a good aesthetic and smooth appearance, which is why many homeowners love using them, especially for fences and facades. However, this type of material is not strong enough for most retaining wall applications, and is not supported by standard Xpress Engineering designs. If you intend to use concrete bricks for your retaining wall, contact Xpress Engineering before ordering a design.
Solid Concrete Blocks
Solid concrete blocks are made to be strong, heavy, and created from naturally dense aggregates, like gravel. This material is strong enough to be used in large masonry units that support heavy loads, including retaining walls.
Solid concrete blocks are similar to concrete bricks, though more expensive. They are also generally quite heavy, which means they can withstand more pressure and weight for a retaining wall. However, this type of material is not supported by standard Xpress Engineering designs. If you intend to use concrete bricks for your retaining wall, contact Xpress Engineering before ordering a design.
Footings & Reinforcement for Concrete Block Retaining Walls
Often the footing for a retaining wall will extend outwards from the face of the wall and/or out the back depending on the type of wall specified by the engineer. This can have an impact on any desired adjacent plantings at the base of the wall.
Also, especially large footings that extend a considerable distance out from the wall can create drainage problems and can also prevent the digging of holes planting shrubs, flowers or trees. For this reason, your contractor should coordinate the footing size and dimensions with desired paving or planting that runs along the face of the retaining wall.
Concrete block stacking methods
There are various stacking systems used for building concrete walls. These include;
- Solid stack – a common stacking system for walls, but generally inappropriate for retaining walls without added mortar and/or rebar.
- Hollow blocks – the retaining wall blocks have a hollow center. This is filled with mortar to create strong and solid retaining wall systems. A structural engineer will also often specify reinforcing bars be added along with mortar to increase the strength and durability of the wall.
- Pin systems – some blocks have pin holes and may even come with pins, which are used to hold the blocks in place.
- Interlocking concrete block systems – This type of block is designed for the blocks to lock together when stacked. The weight of the concrete retaining wall blocks ensures that the wall stays firmly in place. This type of retaining wall is not supported by standard Xpress Engineering designs. Contact us if you’re interested in a custom quote for a retaining wall design of this type.
Retaining Wall Facades and Treatments
Many people believe that cinder blocks are drab and colorless. However, while concrete CMU’s or cinder blocks form the core of the wall, there is a range of veneers that can be used to cover the exterior of such a retaining wall. A variety of natural stone or brick finishes can be used to insure that the wall will blend well into your landscape.
If you prefer to match the walls with the other structures on the property, you can also choose to plaster the wall blocks or use stucco and paint. The choice of finish for your retaining walls is almost endless.
The pros and cons of concrete block retaining walls
There are many advantages to concrete block retaining wall installation but some people may prefer other materials so it’s worth discussing the disadvantages too
The advantages of a concrete block retaining wall
There are many reasons why concrete block retaining walls are so popular. Let’s look at some of the advantages of concrete block retaining walls
- Flexible – Concrete blocks are flexible in use. They can take on curves and angles with ease and you can even include a staircase in the structure
- Strong – concrete is almost indestructible. it requires very little maintenance and should give you decades of trouble-free service
- Fire and weather-resistant – concrete can stand up to strong winds, extremes of temperature, and even flooding. It is fire-resistant too
- Durable – concrete doesn’t rust or rot and it can even resist freeze-thaw cycles
- Good looking – when you think concrete you may think gray. Yet today’s project can take on a range of colors and patterns to fit in with the surrounding structures or the landscape.
- Low maintenance – a washdown and occasional inspection is all your concrete block wall will need
- Affordable – compared to many other materials concrete blocks are cost-effective. Construction is relatively quick so the labor costs are also relatively inexpensive
Disadvantages of concrete block retaining walls
- Height limitation – some concrete block retaining wall designs may not include a footing, which will limit their height to four feet, according to most local building codes.
- Difficult to remove – if you ever decide to demolish your wall, you will most likely find that it would be difficult and costly to remove.
Retaining wall design factors
Retaining walls have to hold back tons of soil which would otherwise slide down without something to hold it back. They must be properly designed by an engineer who fully understands building codes, knows what to look for and how to calculate the forces in play.
Structural engineers must account for all loads brought to bear by the retained soil and any water which might accumulate despite the drainage and pressures caused by surcharges such as roads above the wall system.
Primary considerations for retaining wall design include:
- Soil composition
- Length and height of the wall
- The slopes above and below the wall
- Above and below-ground facilities
- Backfill requirements
- Water table and drainage
- Seasonal weather conditions for the area
- Surcharges above and below the wall system
- Potential seismic activity
- Local building regulations
Engineers must take account of all of these factors individually and as a whole as some of the factors may influence others.
Concrete block retaining wall failures
Concrete block retaining walls are particularly strong and durable so they shouldn’t fail if properly designed. However, it can happen. The main causes of retaining wall failure include the following:
- Improper retaining wall design or reinforcing
- Poor drainage behind the wall blocks creating hydrostatic pressure
- Inappropriate backfill
Professional Engineering Retaining Wall Design – Fast and Affordable
Whichever material you choose for your retaining wall, keep in mind that most local building codes require an engineering design for any retaining wall of 4 feet or more in height. And even for shorter walls, a design from a trained structural engineer is highly recommended to insure the security and longevity of your wall.
We can provide a certified engineer design for you within 24 hours (M-F) for just $350. Submit your Design Request here, or contact us if you have any questions or unique requirements.