How Long Will the Wall Last?

The approximate life of a concrete retaining wall could be between 50 – 100 years, though the National Concrete Association estimates it at 75. This will greatly depend on the quality of installation and the condition of the site.  The soil it is built in and the materials used to construct the project, are key to ensure a proper foundation is beneath the wall and water has been addressed. The next factor is how water is being directed away from the wall.  Water that pools above or within the wall adds pressure to the project and over time may, at a minimum, wash out the base materials which will weaken the wall and limit its lifespan.   But by following the Allan Block installation guidelines, any project should perform for many years.

How Does a Retaining Wall Work?

A retaining wall retains soil similar to how a dam retains water.  A dam’s mass must be large enough to withstand the pressure of the lake that it’s holding back. A retaining wall’s engineering principles are similar.  Even though earth doesn’t move as fast as water, it still applies pressure to a retaining wall just as water does to a dam.  

Dams and retaining walls are also similar in how they are designed.  Many dams are created using compacted soil that is protected with concrete or rocks.  Retaining walls use a similar design where engineers combine compacted soil with geogrid.  Geogrid is a structural building material that helps consolidate the soil into a stronger mass.  It’s a similar concept as putting rebar into concrete.  The combination of soil and geogrid makes a perfect structural reinforcement for retaining it all.  The concrete retaining blocks are the finishing material that adds beauty and provides protection to the soil mass.

A properly designed retaining wall will last a lifetime as long as the compacted mass is protected from water saturation and erosion.  Engineers design many features into their designs to protect it from these situations.  Properly designed retaining wall structures provide pathways to remove excess water from the base and also behind the wall facing.

How long will Allan Block last (life expectancy)?

This is a subject that comes up quite often, but is truly a hard question to answer. Allan Block is manufactured by dozens of different companies around the world, which all have different aggregate and testing on their blocks.  Each block will act differently due to the type of aggregate and manufacturers output product.  With that being said, there is a set of standards that each block manufacturer must meet.  By achieving those minimum requirements, a life expectancy can be calculated.  Since the dry cast block industry looks to the National Concrete Masonry Association (NCMA) for guidance, that is where we can extrapolate a true life expectancy.  The NCMA puts a life expectancy of upwards of 100 years when the product is not exposed to chemicals that increase the breakdown of the concrete.  Since most retaining walls incorporate geogrid reinforcement, we have to look at the life expectancy of that material as well which the NCMA provides guidance of 75 to 100 years.  Since geogrid is the limiting factor in this case, the industry then can use a 75-year life expectancy of a retaining wall block.  With all this information, we have given a long answer to such a simple question!

Can You Have a Driveway or Parking Lot Above Your Wall?

Allan Block segmental retaining walls (SRW) can be designed for virtually any site condition, including all sorts of surcharges.  Surcharges are defined as any external loading condition that is above the wall.  Common surcharges are slopes, driveways, parking lots, roadways, sidewalks, buildings, patios, etc.  Driveways and parking lot loading come from vehicles, of course, and from an engineering standpoint, are considered Live Loads.  Live Loads, like vehicles, are not always there.  They come and go with high loads, and then no loads.  This type of load is perfectly handled by an SRW because they are designed to flex and move.  The geogrid reinforcement interacts with the soils and the block facing to handle these surcharges easily.

The AB Walls Design Software has many versatile surcharge functions built into the programing.  Engineers can put combinations of live and dead load surcharges that are either continuous or line loads.  These combinations provide engineers the flexibility to model virtually any surcharge they will encounter on any project site.

Things to consider with surcharges above your wall, are lengthening the top layer(s) of grid to provide additional strength to the pavement structure above, fences, pedestrian guardrails, and traffic bumpers.  These external conditions all apply a top-of-wall overturning force that the engineer can easily design for.

For more information on AB Walls modeling, surcharges, top of wall overturning, or any other questions related to Allan Block wall design or construction, contact Allan Block at engineering@allanblock.com.

Do I need a permit?

It is always a good idea to contact your local city or county building department for their requirements.  These can typically be found on the city’s website or by giving them a call.  Typically, we have found that any wall over 4 ft (1.2 m) in height will require a permit per the International Building Code (IBC).  Some may also have requirements on length or the location to a property line.

When a permit is required, generally you may need to provide a set of drawings showing the retaining wall location and size.  Depending on the scope of the project, stamped engineering drawings may also be needed.  Allan Block has a pre-engineered manual that can be provided to the city with information and specifications for the product for walls up to 6 ft (1.8 m) in height.  If your city does not already have a copy on file, or if your wall is over 6 ft (1.8 m), contact your local AB Distributor or AB Sales rep for this information.

Checking with your city is always recommended when starting any retaining wall project. To assist in this, visit our website to create a custom residential submittal package.