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  • Writer's pictureEngineer Mike

Most Common Causes of Retaining Wall Failure

Updated: Nov 21, 2023


Retaining walls are very expensive to repair or replace.


The most common causes of damage to retaining walls are usually associated with construction defects, drainage problems, or a combination of the two. Construction defects are due to bad design or deficient installation means and methods.



Previously repaired SRW red masonry retaining wall.
Retaining walls are costly to repair or replace.


To protect retaining walls, good site design must control water, including snow, rain, and natural groundwater. In addition, engineers must select wall materials compatible with site characteristics like the climate, surrounding topography, and site soil conditions. The neglect of any of these critical factors can be a problem.


 

Five Ways Retaining Walls Fail



Wall failure by overturning.

Wall failure by sliding.

Wall failure by undermining.



Wall failure by vertical displacement.

Wall failure by block dislodging.

 

Construction Defects


There are situations when the retaining wall design is technically flawed or a contractor has not constructed the retaining wall per the engineered design documents. If a wall is failing, forensic engineers perform "destructive testing," meaning that specific sections of the retaining wall are disassembled to determine if the wall is correctly constructed and why it is structurally unstable.



Engineer excavating the backfill material behind a retaining wall.
Under the supervision of a forensic engineer, the retaining wall backfill is excavated to expose the characteristics of the soil and geogrid potentially used for soil stabilization.




Destructive testing typically also includes water monitoring, soil sampling, and laboratory testing. This type of forensic evaluation is costly.


Mini-drilling rig excavating a boring in the backfill material of a retaining wall.
At locations of retaining wall failure, samples are retrieved and sent to the laboratory to determine the soil's classification, qualities, and strength.


Engineer checking the monitoring well in the backfill of a retaining wall for water level.
The engineer accesses the monitoring well on the retaining wall to measure the groundwater level. Shallow groundwater from various sources can negatively affect the stability of the retaining wall.

 

Who is Responsible for the Design of Retaining Walls?

The civil engineer, structural engineer, and architect must consider drainage in their design. The civil engineer's intent is to design the overall site infrastructure to divert water from areas where retaining walls are constructed. Considering the soil recommendations provided by the geotechnical engineer and loading, a structural engineer correctly implements drainage structures and drains along the retaining wall. Finally, an architect must design roof, porch, and patio drainage systems to have the most negligible impact on retaining walls.


 

Drainage


Due to its lower cost than other alternatives, one of the most popular retaining walls in residential construction is the Segmental Retaining Wall (SRW), commonly referred to as a masonry block wall. This type of retaining wall is not designed to handle any water seepage or overflow and requires lifetime maintenance to fix water or erosion problems as they occur.


The design of a retaining wall must include a method to properly route water around the top of the retaining wall and away from the bottom.


This is achieved by:

  • Grading diversion swales above the retaining wall.

  • Providing a proper slope at the base of the retaining wall.

  • Ensuring drainage pipes are correctly diverted away from the retaining wall.

  • Adequately diverting roof gutter extensions.



 

Pipe Discharge


Managing roof and sump pump drainage is a very important concept. Roof gutter downspout extensions or sump pump discharge pipes that dump water on, above, or at the base of a retaining wall will cause damage.


Foundation drain sump pump discharging directly at base of retaining wall.  Wet soil at base of retaining wall.
Any pipes discharging water, such as gutter extensions or sump pumps, must be routed away from retaining walls.

 

Efflorescence


One of the first signs of a moisture problem in SRW or brick walls can be the appearance of "efflorescence." Efflorescence is defined as a white, fine, powdery deposit left on the surface of masonry as water evaporates.


Gutter downspout dischardging directly on top of red SRW masonry block retaining wall.
Water can cause damage to retaining walls. In this photo, note the gutter extension discharging directly behind the retaining wall. The efflorescence indicates water seepage through the wall blocks.




 

Staining


Staining on the face of the retaining wall is another sign of a drainage problem. Staining can be from residual soil particles on the face of the retaining wall or stains left by soil minerals, fertilizers, algae, or mold growth.


Staining from water on face of SRW masonry block wall.
Staining on retaining walls is not only unsightly but is a strong indicator of a problem related to drainage.

 

Erosion and Sediment


A sign to look out for is erosion or sediment deposits (small soil particles) around a wall or soil washed away between blocks. Erosion can affect wall stability.


Sediment build-up from erosion on top SRW masonry block retaining wall.
Erosion and the build-up of sediment around a retaining wall are strong indicators of a problem related to drainage.


 

Vegetation Growth


Vegetation between wall blocks or cracks is another sign. Grasses and weeds thrive in well-supplied moisture conditions.


Grass, plants, and vegetation growing in between SRW masonry blocks of retaining wall.
Vegetation, such as grasses and weeds growing around and in the wall, are strong indicators of a problem related to drainage.


 

I hope this information was helpful to you. For additional topics related to construction defects, go to SiteDamage.com.


Visit my photo collections page, which has examples of damage that can be due to construction defects.  





Mike

Engineer Mike





 

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