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Crack in stone retaining wall.

Retaining Walls

Segmental (Block), Concrete, and Stone

Per the International Residential Code, regular landscaping retaining walls four or less feet in height do not require permitting.  Any retaining greater than four feet, or that supports a load on the top side of the wall (such as a roadway or structure) must be designed by a professional engineer, regardless of wall type.

Why Concrete Retaining Walls Fail

Ineffective structural design, seepage (through the mechanism of wicking), water flow into the backfill and at the base can contribute to the failure of concrete retaining walls.  Drainage problems that affect a retaining wall are often caused by uncontrolled surface water runoff and irrigation.

Concrete-retaining walls require weep-holes to alleviate any pressure caused by water buildup behind the wall. 

Ways Retaining Walls Fail

Weight on top of the wall, forces by the retained soil on the wall (sometimes worsened by groundwater), and/or weak soils can cause the failure of a retaining wall.

Diagram of overturning of a retaining wall.
Diagram of sliding of a retaining wall.
Diagram of undermining of a retaining wall.
Diagram of vertical displacement of a retaining wall.
Diagram of block dislodging of a retaining wall.

Common Block Retaining Wall (SRW) Conditions

Walls can fail due to inadequate design, installation, and/or weak soil.  Water infiltration from drainage into the backfill, through the blocks, or at the base is the biggest enemy of the stability and design life of an SRW retaining wall.  Drainage problems are often caused by uncontrolled surface water runoff and irrigation.


For example, SRW walls are not designed for water to flow over or through.  Instead, drainage needs to be routed around, instead of over, SRW retaining walls.  Segmental retaining walls require a pipe system to drain water that builds up behind the wall.


National Concrete Masonry Association (NCMA), the authority  provides the following recommendations in their Design Manual for Segmental Retaining Walls:


  • Water can increase loads on a wall, be a source of scouring or erosion, or decrease the stability of soils around an SRW. 


  • Improper collection and flow of surface drainage can direct excessive amounts of water toward an SRW and cause erosion or over-loading of a wall. 

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Design or construction defects are a typical cause of this condition.

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Settlement or subsidence are common types of wall failure.  These types of failure can be due to deficient design, construction, or drainage.

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Forward rotation is a common type of wall failure.



Staining can be from residual soil minerals, fertilizers, algae, or mold growth.

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The erosion (washout)of soil is caused by water flow.  It affects the soil behind and under the retaining wall, and can result in structural instability.

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Efflorescence is defined as a fine, white, powdery deposit left on the surface of masonry as water evaporates.

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Bad drainage conditions allow grass and weed seeds to germinate and grow in between wall blocks and cracks.

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