A retaining wall is a structural feature designed to prevent downhill soil erosion and soil collapse.
There is a wide range of retaining walls, all of which use the same principle. This is that the earth’s pressure must be offset by an opposing force.
The common signs for retaining wall failure are cracking, tilting, bulging, bowing or buckling. If you are unsure of the integrity of your retaining wall, book in for a building inspection today.
What do retaining walls actually do?
Most commonly erected after excavation or to fill an embankment, a retaining wall is built to withstand many kilograms of soil pressure.
A retaining wall can be used to support a major structure like your home down to minor reasons like a decorative landscaping wall. More often than not, these load bearing walls are constructed using materials like timber, stone, brick or concrete.
Made from such hardy materials, a properly constructed, implemented and the well-maintained retaining wall should last the test of time, however, that’s not always the case.
Common types of retaining walls
Gravity retaining wall
A traditional gravity wall uses its weight to oppose the earth’s pressure. These rigid walls are mainly constructed using concrete and stone as they need to be heavy enough to counteract significant soil pressure.
The gravity wall is constructed with a thicker base and a small backward lean to ensure the soil is held back.
Anchored retaining wall
Anchor walls are ideal if you are working in a tight space or if you need a tall retaining wall to ensure a large amount of soil is held back.
Cables are used to connect the top and the bottom of the wall and they are inserted into concrete footings so that the wall will maintain its integrity.
Sheet pile retaining wall
Ideal for use in softer soils this solid wall is constructed by driving vertical planks into the soil. The sheet pile itself is usually made from steel but timber sleepers can also be used.
These sheet tiling walls are ideal if you are after a space saving solution or if you want to protect adjoining land. Taller sheet pile walls will need to be supported with an anchor.
Cantilever retaining wall
A cantilevered wall is usually made from concrete and it is shaped like the letter L or the letter T.
Its foundations are inserted backward under the soil that it is supporting and then the soil is compacted on top.
This type of wall needs careful planning and design.
Early signs of retaining wall failure
The signs of retaining wall failure can be obvious to the naked eye like the cracking of concrete, bowing of wood or bulging of brick, however, other symptoms may be more discrete like inadequate sub-soil drainage or surrounding soil collapse.
Bowing or cracking
If your retaining wall is not looking like it should, chances are there are some problems with the structure itself or what is happening behind it.
If your retaining wall begins to bow or crack, you can reinforce the ailing structure with reinforcements and anchors.
When built correctly, a retaining wall will have a sub-soil drainage system behind it or weep holes to allow water to drain from behind the structure.
If there is a buildup of water behind the wall, the wall can become quickly unsafe with the situation calling to be remedied quickly.
Surrounding soil collapse
Surrounding soil collapse, otherwise known as subsidence refers to a sinking of the soil in the area around the retaining wall structure.
If the soil around your structure suddenly sinks, then it’s a good indication that the pressure on your retaining wall has changed and that it may no longer have the opposing force necessary to keep it in check.
Causes of retaining wall failures
Incorrect load calculation
Before you begin your retaining wall project, forethought must go into accurately estimating how much load it will have to bear.
f you have incorrectly calculated the load, the structure will not be able to cope and will potentially fail.
Improper installation and cutting costs
All retaining walls are not created equally. If the right retaining wall has not been chosen for the job or it has been incorrectly installed, failure may be imminent. Likewise, if cheap materials have been used to create the structure, wall failure and collapse may be brought forward in time.
When a retaining wall is built to last, it will have a sub-soil drainage system behind it.
This will collect water from below the ground surface and behind the wall and direct the water to flow toward the closest stormwater drain.
Larger retaining walls might have weep holes built into them to help alleviate the water pressure. If these systems have become clogged or not installed initially, it will lead to the soil behind the wall becoming saturated.
Once the backfill becomes wet, the force needed to hold up the soil has changed which may lead to the failure of your retaining wall.
Even with the best intentions, meeting building standards, quality products and the best drainage, you won’t be able to save your retaining wall from old age.
Typically, timber retaining walls should last around 20 years and concrete and brick should last up to 100 years.
How to prevent retaining wall failure
When calculating the load for your retaining wall, it’s useful to err on the side of caution and be conservative.
Before you begin working through the figures, it’s imperative to investigate the site, consider the soil type and take precise measurements to correctly calculate the load your wall will need to survive.
Qualified builders and materials
To create a retaining wall that looks good and does the job, it’s imperative to use the right people, the correct type of retaining wall and quality products. Now’s not the time to cut corners!
Wet soil weighs a lot more than dry soil so, including a drainage system at the beginning of your retaining wall build is a must. Choosing the correct backfill and drainage system will help you to ensure that water doesn’t pool behind your wall.
It’s imperative that you or your builder check with your local council to see whether permission is needed for your retaining wall or if you need to engage an engineer and building surveyor.
Why you need a building inspection
As we’ve outlined, retaining walls are not built for their looks alone. They are built for a purpose and that purpose is to quell downhill soil erosion and soil collapse. If a retaining wall is unstable and cannot do its job, the consequences can be costly and dangerous to your family.
Unfortunately, as we mentioned previously, retaining wall issues may not be immediately apparent to the untrained eye.
There’s usually much more going on out of sight than you may realise. That’s why you need a building inspection report so that you can understand the health of your retaining walls.
Our standard building inspection and our pre-purchase property inspection includes the detection of structural damage on your non-structural retaining walls.
This information will be beneficial to you moving forward in your decision to buy a property and to adequately negotiate a fair price if there is damage to any of the non-structural retaining walls.
Contact us for an inspection
If you would like more information about what your inspection will cover or would like clarification on anything we’ve mentioned in this article, contact our expert team at Inspect My Home by calling 1300 337 447 or by submitting an enquiry online.