How to Build Stronger Retaining Walls (2023)

Get strong, long-lasting retaining walls by learning how to properly build a wall.

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How Soil ‘Pushes’ (and How to Build a Retaining Wall that Pushes Back)

When you contemplatehow to build aretaining wall, you may imagine how firm and solid it’ll appear from the front, or how great the new garden will look above it. But unless you give serious thought to what goes on behind and below the wall, the retaining wall design may not look good for long. A poor retaining wall design wall can lean, separate, even topple — you don’t want that.

Lots of people think a retaining wall needs to hold back all 6 gazillion tons of soil in the yard behind it. It doesn’t. It only needs to retain a wedge of soil, or elongated wedge of soil, similar to that shown in the image below.

(Video) How to Build a Retaining Wall and 6 Reasons they Fail

In simple terms: Undisturbed soil — soil that has lain untouched and naturally compacted for thousands of years — has a maximum slope beyond which it won’t ‘hang together’ on its own. This slope is called the failure plane. If left alone, the soil behind the failure plane will stay put on its own. But the soil in front of the failure plane — the natural soil or the fill you’re going to add — wants to slide down the failure plane.

How to Build Stronger Retaining Walls (1)Family Handyman

Gravity, along with the slope, directs most of the weight and pressure of the fill toward the lower part of the retaining wall. Since soil weighs a beefy 100-plus lbs. per cu. ft., you need some pretty heavy material — large retaining wall blocks, boulders, timbers or poured concrete — to counteract the pressure. Just as important, it needs to be installed the right way. Here are three key principles in building any solid retaining wall:

  • Bury the bottom course, or courses, of the retaining wall one tenth the height of the wall to prevent the soil behind from pushing the bottom out.
  • Step back the blocks, rocks or timbers to get gravity working in your favor. This lets the walls lean and push against the fill. Walls built perfectly vertical get gravity working against them the second they start leaning outward even just a bit. Most concrete retaining wall block systems have some kind of built-in lip or pin system that automatically creates the step back as you build.
  • Install a base of solidly compacted material so your wall stays flat. A level wall provides modular blocks, stone and timbers with more surface contact with the courses above and below them. They fit together more tightly. The more contact, the more friction and the stronger the wall. Apply these three rules, and you’ll create a strong wall. But even a well built wall won’t survive unless you take care of two troublemakers: water and uncompacted soil.

Uncontrolled Water Weakens Walls

Water can weaken retaining walls by washing out the base material that supports the wall. But far more frequently, it causes problems by building up behind the wall, saturating the soil and applying incredible pressure. That’s when walls start leaning, bulging and toppling. Well built walls are constructed and graded to prevent water from getting behind the wall and to provide a speedy exit route for water that inevitably weasels its way in.

Take a look at the well-drained wall below on the left. The sod and topsoil are almost even with the top block, so surface water flows over the top rather than puddling behind. Just below that is 8 to 12 in. of packed impervious soil to help prevent water from seeping behind the wall. The gravel below that soil gives water that does enter a fast route to the drain tile. And the perforated drain tile collects the water and directs it away from the base of the wall, escorting it out through its open ends. There’s nothing to prevent water from seeping out between the faces of the blocks, either; that helps with the drainage too. The wall even has porous filter fabric to prevent soil from clogging up the gravel. What you’re looking at is a well-drained wall that will last a long time.

Now look at the poorly drained wall below on the right. There’s a dip in the lawn that collects water near the top of the wall. There’s no impervious soil, so the water heads south, slowly water-logging and increasing the weight of the soil packed behind the wall. The homeowner put plastic against the back of the wall to prevent soil from oozing out between the cracks — but it’s also holding water in. Yikes! There’s no drain tile at the bottom — the trapped water can soak, soften and erode the base material. Not only that, an excavated trench that extends below the base lets water soak into the base material and weaken it. You’ve got a retaining wall that has to hold back tons and tons of water and saturated soil — and when that water freezes and expands in the winter, matters get even worse.

(Video) How to build a strong retaining wall that does not lean.

How to Build Stronger Retaining Walls (2)Family Handyman

A Well-Built Wall

A strong retaining wall design features well-compacted base material, compacted material in front of the wall to prevent kick-out, and stepped-back materials.

How to Build Stronger Retaining Walls (3)Family Handyman

A Poorly Built Wall

A wall that has an uneven base, no compacted material in front of it and no step-back to the materials will eventually fail.

How to Build Stronger Retaining Walls (4)Family Handyman

Poor Compaction Adds Pressure to Walls

Even if you have only a small wedge of soil to retain, compaction is important. If your failure plane is farther back so your wall needs to retain more fill, weight and pressure, then compaction and a reinforcing grid become critical. These two things help increase internal friction and direct the pressure of the fill you add downward, rather than at an angle pushing against the wall. Good compaction doesn’t mean dumping a couple of feet of fill behind the wall, then jumping up and down on it in your work boots.

(Video) Concrete Retaining Wall

Good compaction means adding 3 or 4 in. of material, compacting it with a heavy, noisy vibrating plate tamper from your friendly neighborhood rental yard, then repeating these steps over and over. Your landscape supplier or block manufacturer (if you’re using modular blocks) can tell you whether you need to install reinforcing grid, and at what intervals. The taller the wall, the more likely you’ll need reinforcing grid.

How to Build Stronger Retaining Walls (5)Family Handyman

When building a retaining wall, never backfill with, or compact, topsoil; it will break down and settle, creating a water-welcoming trench behind your wall. Use sandy or gravelly materials, which compact much better. And always make certain you don’t become overzealous and compact your wall outward.

Timber Walls, Tall Walls, Building Codes and Other Stuff

By themselves, landscape timbers and a railroad tie retaining wall lack the weight to hold back soil. To make these walls strong, you need to add “dead men,” anchors that lock the wall into the soil behind them. The same pressure that’s pushing against the wall pushes down on the dead men to keep them (and therefore the wall) in place. The principles of stepping back, installing good drainage and compacting also apply to timber walls.

How to Build Stronger Retaining Walls (6)Family Handyman

Walls of any material that are taller than 4 ft. play by the same rules — it’s just that the wedge of soil is too big and heavy to be held in place by the weight of the materials alone. Some communities now require building permits and construction details for walls exceeding 4 ft. in height. We think that’s a good idea too. Many modular block manufacturers can supply printed sheets of structural information.

(Video) How to build a Retaining wall STEP BY STEP!

For tall slopes, a series of tiered walls is a good substitute for a single tall wall. But an upper tier can apply pressure to a lower tier unless it’s spaced the proper distance—you know, behind the failure plane. The rule of thumb is to set back the upper wall twice the height of the lower wall.

Popular Videos

(Video) How to Build a Retaining Wall - Step by Step


How do you make a retaining wall stronger? ›

The wall can be strengthened by transferring some of the shear force to the base where the wall meets the ground. This can be done by either extending the footing of the base or placing concrete to thicken the base. Installing anchors or tiebacks is another option for extra strength.

How do you make a weak wall stronger? ›

  1. Methods to Strengthen Concrete Walls.
  2. Concrete Jacketing.
  3. Concrete Replacement.
  4. Retrofitting by Steel Materials.
  5. Retrofitting using Shape Memory Alloys (SMA)
  6. Use of FRP Laminates.
May 3, 2019

What is the strongest type of retaining wall? ›

Concrete and Masonry Retaining Walls

Poured concrete is the strongest and most durable choice for retaining walls. It may also be carved and formed to look like mortared stone depending on your taste.

What attributes make a good retaining wall? ›

A strong retaining wall design features well-compacted base material, compacted material in front of the wall to prevent kick-out, and stepped-back materials.

How do you strengthen a wall? ›

The key element used in structural wall strengthening are wall ties, also known as brick ties. These are used in properties that are built with cavity walls, to join the two leaves of the brickwork together. This makes them united and a strong unit that forms the internal and external walls of the property.

How do I stop my retaining wall from leaning? ›

Wall anchors can be a long lasting solution to strengthen retaining walls and actually pull them back as close to their original position as possible. Wall anchors can be used to shore up bowed or leaning basement walls, but the same solution can be used in your retaining walls.

How do you keep retaining wall blocks from moving? ›

DO start with a good foundation. Your retaining wall will only be as strong its support system. For a stacked-block retaining wall that's no higher than four feet, a trench filled with three inches of crushed rock will help keep the wall from shifting and settling.

What causes retaining walls to fail? ›

The number one cause of retaining wall failure is poor drainage. If too much water gets absorbed into the soil behind the wall, the hydrostatic pressure can push on the wall causing it to bow out or crumble.

What is the best material to put behind a retaining wall? ›

Backfill the wall with gravel or sand. If you use sand, first cover the backside of the retaining wall with landscape fabric. This will keep the sand from seeping between the blocks. If you're backfilling with gravel, you can pour the gravel after every course you lay.

What is the best material to backfill a retaining wall? ›

The best material for the backfilling of a retaining wall is gravel, and it should be well graded. The main reason for using gravel is because it does not retain water (small void ratio); hence lateral loads experienced will be minimal. You should also have weep holes for draining excess water that may be retained.

What is the best base for retaining walls? ›

Base material

The base material should only consist of angular, sharp-edged particles such as ¾-inch minus gravel. The various-sized crushed gravel with the fines helps ensure the right amount of compaction. Round rocks, such as pea gravel, roll and dislodge under pressure resulting in failure of the retaining wall.

How thick should a retaining wall be? ›

One of the things you must get right is the thickness of the wall. It should be at least 215mm thick and bonded or made of two separate brick skins tied together. This should be enough in most cases with minimal water pressure or where the ground level difference is less than a metre.

What are the best blocks for retaining wall? ›

Concrete blocks are ideal for building walls to hold back the soil after you dig into a slope for a pathway, patio, or another landscaping project.

What are the types of wall strengthening? ›

The most familiar strengthening methods are: partial and overall re-laying of the wall, steel tie-beams, low- or high-pressure injection, strengthening steel bars stacked into the wall's joints or strengthening by the use of steel and concrete elements.

How do you reinforce a wall without studs? ›

Use a toggle bolt or anchor to hang the piece on areas with no studs, This Old House says. The weight of the piece , and the thickness of the wall, will dictate the toggle size. The typical metal toggle bolt can hold 25 to 50 pounds on plaster, according This Old House. A plastic one can hold 10 to 25 pounds.

What is a strong material for a wall? ›


This is the most commonly used wall material. It is strong, durable, and has excellent resistance to wind and fire.

How much weight can a retaining wall hold? ›

Even small retaining walls have to contain enormous loads. A 4-foot-high, 15-foot-long wall could be holding back as much as 20 tons of saturated soil. Double the wall height to 8 feet, and you would need a wall that's eight times stronger to do the same job.

What is the best gravel for drainage behind a retaining wall? ›

The best gravel for using underneath a brick patio or concrete block retaining wall is often referred to as “processed gravel” “crushed base” or “bank run gravel.” This type of gravel has a mixture of fines that aid in compaction. It may look like sand with rocks in it.

How far can a wall lean without falling? ›

Generally speaking you should be concerned with anything more than 25mm of distortion as it lowers the stability of the wall. There is a general rule known as the V3 rule, which asks that you consider the walls centre of gravity.

Does a retaining wall need to be angled? ›

It should be built in a way that makes it easy to hold the soil. For that reason, it should be slanted at an angle between six to twelve degrees, depending on the slope. Such a retaining wall is referred to as a setback.

What causes a retaining wall to slide? ›

Sliding occurs when horizontal force equilibrium is not maintained (i.e., when the lateral pressures on the back of the wall produce a thrust that exceeds the available sliding resistance on the base of the wall).

Do you need landscape fabric behind retaining wall? ›

A barrier behind the wall, lined in fabric and filled with gravel, creates an area for water collection and movement. The fabric helps keep the voids in the gravel from packing with silt. Leave room above the gravel backfill for topsoil or bedding soil.

What will damage retaining wall? ›

A common cause of retaining wall failures is a design that does not provide for or a contractor who does not install sufficient drainage behind the wall. Without proper drainage elements, a retaining wall will cause water to build up in the soil behind the wall.

How do you know if a retaining wall is stable? ›

For stability, a retaining wall should satisfy the following conditions: The wall should be stable against sliding. The factor of safety against sliding should be minimum of 1.5. The wall should be stable against overturning. For granular backfill, the factor of safety against overturning shall be minimum of 1.5.

What happens if you don't put drainage behind a retaining wall? ›

If there is no drainage, water will compromise the safety and structure of your retaining wall. It's vital that the wall is repaired or replaced if measures to ensure drainage weren't taken. This can lead to an extensive amount of damage on the property, the expense of repairs and installation of a new wall.

Why does my retaining wall keep cracking? ›

One of the main causes of a broken concrete retaining wall is poor drainage, so make sure that you improve drainage around your wall to mitigate the likelihood of it leaning. Reinforce the retaining wall to make it stronger and prevent future leaning. Add weep holes to improve drainage.

What are the main failure causes of a retaining wall? ›

What causes a retaining wall to fail? A retaining wall will fail when it is unable to withstand the force on it created by the soil behind it. A retaining wall failure can be the result of an inadequate design for the wall or the improper construction of the wall.

WHY DO retaining walls fall over? ›

Frequently, retaining walls fall because they were not properly reinforced when they were installed. Sometimes, if the wall is installed by someone who is not properly trained, there will be no reinforcement at all. When this is the case, walls cannot withstand the test of time.

What is the best block to use for a retaining wall? ›

Concrete blocks are ideal for building walls to hold back the soil after you dig into a slope for a pathway, patio, or another landscaping project.

Should you glue every block on retaining wall? ›

Retaining wall blocks typically do not need adhesive to lay each course. If you wish to lay more than two courses, you only need to cut a block in half for the even-numbered courses.

What affects the stability of a retaining wall? ›

However, a retaining wall may lose stability or collapse under the influences of many factors (such as variations in temperature or humidity, material degradation, and load variation). Additionally, some terrible accidents may occur once the wall collapses.

What are the signs of retaining wall failure? ›

The common signs for retaining wall failure are often cracking, tilting, bulging, bowing or buckling. Fractures in the wall can often prevent the structure from retaining the soil. At this point, the wall may be retrofitted with reinforcements like anchor bolts to rectify bowing before a total collapse.

Does a 2 foot retaining wall need drainage? ›

Every retaining wall should include drainage stone behind the wall. Though it is a good idea to install a drainage pipe on all walls, there are certain situations where a perforated drain pipe is absolutely necessary.

Do retaining wall blocks need to be perfectly level? ›

Step Four: Set First Layer of Retaining Wall Blocks

As you lay each block next to each other, use your level to ensure everything lines up perfectly. Not only do the blocks need to be level, but they need to be flat and level relative to each other.

What is best to backfill a retaining wall? ›

The best material for the backfilling of a retaining wall is gravel, and it should be well graded. The main reason for using gravel is because it does not retain water (small void ratio); hence lateral loads experienced will be minimal. You should also have weep holes for draining excess water that may be retained.

How thick should my retaining wall be? ›

One of the things you must get right is the thickness of the wall. It should be at least 215mm thick and bonded or made of two separate brick skins tied together. This should be enough in most cases with minimal water pressure or where the ground level difference is less than a metre.


1. How to Build a Retaining Wall (Step-by-Step)
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2. The best and most economical retaining wall system / by The Solutioneers
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3. Engineering trick to strengthen retaining walls, and rock delievery
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4. 7 Commonly Overlooked Retaining Wall Install Mistakes that Lead to Failure
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5. Retaining walls- what 99% of people don't know
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