Understanding why retaining walls fail is the first step in preventing issues and applying cost-effective solutions. This article explores the most common causes of retaining wall failures and the best methods to fix or prevent them.
Retaining walls play a crucial role in stabilizing slopes, preventing soil erosion, and creating usable space in hilly or uneven terrain. However, their failure can lead to costly repairs, property damage, and even safety hazards. The image above is an extreme example of a retaining wall failure. In this case, the structure lacked proper permits, an engineer’s oversight, adequate reinforcement, and essential construction details such as grouted cells.
Sometimes, a retaining wall does not have to experience total collapse to be considered a failure. Signs of distress, such as excessive tilting, cracking, or bulging, often serve as early warnings that the soil retaining structure may become unstable over time.
Understanding why retaining walls fail is the first step in preventing issues and applying cost-effective solutions. This article explores the most common causes of retaining wall failures and the best methods to fix or prevent them.
What Constitutes Retaining Wall Failure?
A retaining wall failure does not always mean a catastrophic collapse. In many cases, signs of distress appear long before the structure completely gives way. Common warning signs include excessive tilting or leaning, cracks that develop due to stress or soil movement, and bulging or bowing of the wall caused by excessive lateral earth pressure.
Water seepage and drainage issues can also signal potential failure, as water buildup behind the wall increases pressure, making the structure unstable. Additionally, settlement or movement in the foundation can cause the wall to shift over time. A properly designed retaining wall should have built-in safety measures to prevent failure, but once signs of distress appear, early intervention can save the structure before total failure occurs.
Common Causes of Retaining Wall Failures
Here are twelve primary reasons why retaining walls fail:
1. Reinforcing Steel Not Placed Correctly
The strength of a retaining wall relies heavily on the proper placement of reinforcing steel. Reinforcing bars (rebars) provide the necessary tensile strength to resist bending forces, and when they are misplaced or insufficiently embedded in concrete, the wall may not be able to withstand lateral soil pressure. Errors in placement often include reinforcement being positioned too close to the soil-facing side instead of the tension zone of the wall, incorrect rebar spacing that reduces the wall’s overall strength, or insufficient embedment depth of dowels into the footing.
A professional evaluation using a Pachometer, a device that detects embedded metal in concrete, can help identify reinforcement issues. If deficiencies are found, solutions may include adding external reinforcement, grouting missing cells, or, in severe cases, reconstructing the wall.
2. Saturated Backfill Increases Pressure
Retaining walls are typically designed with well-drained backfill material, such as crushed rock or gravel, to minimize pressure. However, if water accumulates behind the wall, hydrostatic pressure can significantly increase the force acting against it, often leading to failure. This usually happens due to poor grading that directs water toward the wall instead of away from it, improper irrigation, or the use of clay-rich backfill that holds moisture instead of allowing proper drainage.
To prevent water-related failures, surface grading should always direct water away from the wall. Installing drainage channels, weep holes, and perforated pipes can also help control water buildup behind the structure.
3. Clogged or Insufficient Weep Holes
Weep holes are designed to allow trapped water to escape from behind a retaining wall, reducing hydro-static pressure. However, they often become clogged with dirt and plant roots, rendering them ineffective. When this happens, water remains trapped, increasing pressure and potentially causing the wall to bulge or crack.
To prevent clogging, proper filtering materials such as crushed rock, gravel, or drainage fabric should be used. Additionally, perforated pipes can help direct water away from the base of the wall, ensuring efficient drainage. Regular inspections and cleaning of weep holes can help maintain their functionality over time.
4. Design Errors Due to Misinformation
Even when an experienced engineer designs a retaining wall, errors can occur if the information provided is inaccurate. A common issue is designing a wall for an intended height, only for the site conditions to change, leading to an increase in retained height without adjustments to the design. For example, if a wall was originally designed to retain 8 feet of soil but is later required to support 9 feet, the bending moment at the base could increase by nearly 50%.
Other problems arise when additional loads, such as heavy equipment or structures above the wall, are introduced without considering their effects. Proper site assessments and clear communication between designers, clients, and contractors can help prevent such design issues.
5. Calculation Errors
Errors in calculations, though rare among experienced engineers, can lead to an under-designed retaining wall. Overlooking key stability factors such as sliding resistance, overturning moments, or bearing capacity can result in a wall that is unable to perform as expected.
This issue is particularly common among inexperienced engineers or designers who rely too heavily on software without cross-checking results using manual calculations. A peer review or verification by another professional can help catch these errors before construction begins.
6. Unanticipated Loads and Surcharge Pressures
A retaining wall may be designed for a particular load, but additional, unforeseen forces can lead to failure. Unexpected loads may come from vehicle traffic, construction equipment, or even changes in soil conditions. For instance, if heavy machinery operates near the top of the wall, the added weight increases lateral earth pressure beyond what the wall was originally designed to handle.
Similarly, the presence of fences or structures on top of the wall may introduce additional wind loads, further stressing the structure. If a wall is experiencing excessive movement due to these factors, it may require reinforcement, tie-backs, or even a redesign.
7. Software Input Errors
Structural design software provides engineers with powerful tools to analyze retaining walls, but incorrect data input can produce unreliable results. Even a small mistake, such as entering the wrong soil parameters or surcharge loads, can result in an underperforming wall. Engineers using software should have a solid understanding of manual retaining wall design principles to verify their results. A cross-check using simplified hand calculations can help identify inconsistencies and ensure accuracy.
8. Poor Reinforcement Detailing
If reinforcement bars are not clearly detailed on construction drawings, contractors may misinterpret them, leading to improper placement. Some common detailing errors include dowels embedded too shallowly or rebars placed on the wrong side of the wall, making them ineffective. To prevent these issues, engineers should ensure that construction drawings contain clear and precise reinforcement details. A pre-construction meeting between engineers and contractors can also help clarify any uncertainties before work begins.
9. Foundation Problems and Soil Conditions
The stability of a retaining wall depends largely on the soil it rests upon. Weak or improperly compacted foundation soil can cause excessive settlement, leading to cracks and tilting. In some cases, the wall may experience sliding failures, especially if it is built on loose or sandy soil. A geotechnical investigation before construction is essential for determining the soil’s properties and ensuring a strong foundation. If no soil report is available, conservative design values should be used, with additional safety factors incorporated to account for unpredictable conditions.
10. Inadequate Construction Specifications
Generic or poorly written construction notes can result in misinterpretations, leading to costly mistakes. Specifications should always match the actual project conditions rather than using generic boilerplate text. Including clear directives on what to do if unexpected conditions arise during construction can help ensure the wall is built correctly.
11. Poor Workmanship and Shoddy Construction
Retaining walls that are built without professional oversight often suffer from quality issues, including inadequate reinforcement placement, poor-quality concrete or mortar, and insufficient compaction of backfill. These deficiencies weaken the structure and increase the likelihood of failure. Hiring an experienced contractor and conducting quality inspections throughout the construction process can help prevent these problems.
12. Age-Related Deterioration
A well-built retaining wall can last for several decades, but over time, materials degrade. Issues typically arise only when new loads or changes in drainage conditions affect the structure. If a wall has been standing for many years without distress, regular inspections can help ensure it remains stable.
Common Fixes for Retaining Wall Issues
1. Improve Surface Drainage
Redirecting surface water away from the retaining wall prevents excessive moisture buildup. This can be achieved by regarding the soil, installing drainage channels, or adjusting irrigation systems to reduce water infiltration.
2. Reduce Retained Soil Height
Lowering the height of retained soil can decrease pressure on the wall. This may involve regarding the landscape or incorporating retaining terraces instead of a single high wall.
3. Install Tie-Backs or Soil Nails
When a wall is severely overstressed, tie-backs or soil nails can provide additional support. These reinforcements anchor the wall to deeper, more stable soil layers, preventing further movement.
4. Extend the Footing
A wider footing increases stability by spreading the load over a larger area. If necessary, the existing footing can be extended with reinforced concrete to enhance load-bearing capacity.
5. Replace Poor Backfill Material
If saturated or expansive soil is causing problems, replacing it with well-draining crushed rock or gravel can improve stability. This prevents excessive pressure buildup behind the wall.
6. Strengthen the Wall with Additional Concrete
A weak wall can be reinforced by applying a layer of concrete over the existing structure. This method increases strength and redistributes loads more efficiently.
7. Add a Key to Prevent Sliding
Installing a key—a vertical extension of the foundation into the soil—enhances resistance against sliding. This approach is effective when movement is detected early.
8. Use Soldier Beams for Extra Support
Inserting vertical steel beams behind the wall can provide lateral reinforcement. These beams act as secondary supports to counteract excessive soil pressure.
9. Secure Proper Permits and Inspections
Ensuring that the wall complies with local building codes helps prevent legal and structural issues. If a wall was built without a permit, it is advisable to get an engineer’s assessment for compliance.
10. Realign the Wall if Slightly Out of Plumb
If a wall has shifted slightly, it may be possible to push it back into position before the problem worsens. However, this should only be done under controlled conditions with professional oversight.
11. Demolish and Rebuild if Necessary
If a retaining wall is beyond repair, rebuilding may be the most cost-effective solution. A new design can incorporate better materials, reinforcements, and drainage solutions to prevent future failures.
12. Innovative Custom Solutions
Each retaining wall issue is unique, and sometimes an unconventional fix may be the best solution. Engineers can develop site-specific reinforcements based on structural assessments.
Conclusion
Retaining walls are essential for soil stabilization, but poor design, drainage problems, and construction errors can lead to failure. Recognizing warning signs like leaning, cracking, or water buildup can help prevent costly repairs or collapses. By addressing these issues early and implementing these fixes, most retaining walls can be saved without complete reconstruction. Whether through improved drainage, additional reinforcements, or foundation adjustments, taking proactive measures ensures long-term stability and safety.
Also See: Design of Embedded Retaining Wall: Worked Example
Sources & Citations
- Bowles, J. E. (1996). Foundation Analysis and Design (5th ed.). McGraw-Hill.
- Das, B. M. (2010). Principles of Foundation Engineering (7th ed.). Cengage Learning.
- Coduto, D. P., Yeung, M. R., & Kitch, W. A. (2016). Geotechnical Engineering: Principles and Practices (2nd ed.). Pearson.
- Brooks, H. (2025). Retaining Wall Failures and Cost-Effective Fixes.
