Retaining walls offer a solution to sloped yards to be able to create a functional space by retaining the material behind them. We specifically build segmental retaining walls due to their aesthetic appeal in a landscape as well as their functionality to be able to withstand the forces applied on it. They do not require mortar and they work together to be both a rigid and flexible system in our freeze-thaw climate cycles that are experienced. However, without the proper construction of these walls they too can fail.
How Long Do Segmental Retaining Walls Last
There are several types of retaining walls including segmental retaining walls, wood railroad tie, natural stone, gabion baskets, and concrete among others. There are pros and cons to each of these and should be weighed depending on the application. If any of these retaining walls are not built properly from the base preparation to the surrounding landscape, they will most definitely fail regardless of the type of retaining wall it is.
If the wall was built properly in the first place, wooden railroad tie walls will only last as long as the wood will last before they start to rot out. Large natural stone walls will provide substantial support considering the weight of that natural stone being the main factor of retaining material behind it, but irregularities in the natural stone may make it difficult to lay level and cause that wall to show signs of failure. Gabion baskets provide appropriate drainage throughout the entire system. Concrete will crack over time with the pressure added to it from behind the wall and ground movement. Segmental retaining walls provide a rigid and flexible system to be able to withstand the pressure and ground movement.
We install segmental retaining walls because when built properly they provide a single mass and the ability to resist shear force from unit-to-unit from forces behind the wall. These wall units interlock and are dry-laid while being built on a flexible base system the same that interlocking concrete pavement is installed upon.
How Long Do Segmental Retaining Walls Last
We have projects that are 10+ years old using segmental retaining wall block that still look as good as the day that they were installed. In reality, a segmental retaining wall should last for a long time as long as it was engineered for the application and the factors to which it was engineered for have not changed. For example, if a simple retaining wall was built to only retain soil but years later a driveway was installed beyond the retaining wall, it may have not been built to withstand the dynamic load of the vehicles and could start to show signs of movement outwards from this added pressure.
When we build retaining walls we refer to manufacturer’s specifications for a specific wall block and the height to which it can be installed to. Some retaining wall blocks can be built taller based on the dimensions of those blocks, as well as the addition of a batter / setback or backwards angle on the wall, and geogrid to stabilize the material in behind the wall. Once a retaining wall exceeds three feet in height, depending on your region you may require outside engineering to have that wall designed for that specific application.
There are numerous examples of segmental retaining walls lasting decades upon decades while the manufactured segmental retaining wall block system was first conceived in the 1960s and became increasingly popular in the 1980s onwards. Today, segmental retaining wall blocks have been embraced as a solution to retaining wall applications.
The main factors that will affect the lifespan of a segmental retaining wall are:
- Materials
- Construction
- Environment
Most reputable manufacturers stand behind their segmental retaining wall block with a limited lifetime warranty. Though you should always check the fine print of these warranties as they usually include that they need to be properly installed based on the manufacturer’s requirements, maintenance, appropriate de-icing agents if applicable as these can degrade your wall block, and does not cover efflorescence.
Efflorescence is a naturally occurring white powdery residue deposited on the surface of the wall block and is caused by the presence of moisture. As that moisture makes its way to the surface of the stone, it will bring with it minerals from within the concrete and deposit them on the surface. Efflorescence should go away after some time, but if it is persistent it could point to a larger problem with the drainage system behind the retaining wall and a precursor to failure of that wall system.
The construction of any retaining wall begins with the knowledge of building walls to the manufacturer’s specifications and to the onsite conditions. Typically a segmental retaining wall is built on at least 6 inches of base material with 6 inches of base in front of the wall block and a minimum of 12 inches behind the wall block. Additionally, a minimum of 6 inches of the wall block is to be embedded below the final grade with this increasing depending on the load behind the wall and slope and soil conditions in front of that wall. The 12 inches behind the wall is an area for drainage stone to be installed as well as a perforated drainage pipe to be exited from the face of the wall every 25 feet. This drainage area is built up with the wall after every course of the wall is laid. Uniaxial geogrid is used where necessary based on the manufacturers specifications to stabilize the backfill area and a batter or setback is placed on the wall which angles the wall into the backfill area as it is built up. Upon completing the wall, a swale is formed to direct water away from the wall and direct it elsewhere.
Check out our full segmental retaining wall installation guide.
Poor water management of the retaining wall system will lead to a lot of different failures in a retaining wall. The more water that is present behind the wall will increase the force or pressure on that wall and in climates that experience freeze-thaw cycles, that water will freeze and expand to add to the force on the wall. This is why drainage behind the wall is so important to the longevity of the wall, as well as management of the water through the face of the wall.
If a wall was not engineered to the height, load that it will retain, and surrounding environment it too could be susceptible to failure. Selection of material for the application and proper construction methods are incredibly important to ensure that wall is going to last for a lot of time to come. Additionally, if environmental factors change during the course of that wall’s lifespan this could add to the pressure placed on the wall that it was not initially designed for.
Why Do Retaining Walls Fail and What Are the Signs
Retaining walls fail because of improper engineering and construction. Segmental retaining walls should be built on a base using appropriate base material as described above at a depth of at least 6 inches and compacted using a compactor that meets the requirements of the lift or height of that base material.
Signs of retaining wall failure could include:
- Efflorescence
- Leaning
- Sinking
- Soil Erosion
If efflorescence is persistent, this could point to a drainage issue in behind the wall. If drainage material was not installed behind the wall there will be moisture buildup that has only one way of getting out of that system and that is through the face of that wall. With that moisture brings efflorescence and is deposited on the face of the wall. This could be a precursor to that wall facing hydrostatic pressure which will cause that wall to lean forward or bow out.
If a wall was not built properly or improper materials were used for the height and force that the wall will withstand in its lifespan, then it will start to lean forward only getting increasingly worse over time with gravity now working against it. This can be caused by improper building techniques, hydrostatic pressure, or forces beyond the wall.
If your retaining wall is showing signs of sinking or the lines are no longer level, this is likely due to improper base construction and compaction of that base. Over time that wall will sink in areas that are experiencing settlement and the wall will move with that base material as it sinks. It could also reveal a weak spot in that wall as forces act on it from behind and start to bow outwards.
Soil erosion at the toe or in front of the wall could cause that wall to kick out in those areas. This can be caused to poor water management in front of that wall as the water has nowhere else to exit the system except in front of that wall. This will expose the embedded course of the wall and eventually the base material which will also erode away with that same washout that the soil experienced.