Retaining walls might not be the flashiest part of your yard, but they play a big role; keeping soil where it’s supposed to be, preventing erosion, and even protecting your home. But when they fail, the results can be costly and even dangerous. According to the American Society of Civil Engineers, bad design or poor maintenance of retaining walls leads to thousands of property damage cases every year, racking up around $200 million in total damages. Even more surprising? About 30% of retaining walls fail just a few years after they’re built.
These failures often stem from common issues like improper drainage, inadequate reinforcement, or poor construction practices. But don’t worry; with a little awareness, these failures are often preventable and fixable. With the right materials, design, and upkeep, most retaining walls can last over 50 years. So, let’s break down the most common retaining wall failures and their solutions to fix these issues before they become a major headache.
Early Warning Signals of Retaining Wall Failures
Let’s begin by going through some of the early retaining wall failure signs:
- Bulging or Bowing of the Wall Face: Indicates pressure behind the wall exceeds its resistance; may signal water buildup or inadequate reinforcement. This symptom commonly precedes structural failure and is typical in several retaining wall failure types involving poor load distribution.
- Leaning or Tilting of the Wall: A critical sign of instability often due to foundation movement or excessive backpressure.
- Water Seepage or Saturation Behind the Wall: The Presence of water or wet stains suggests poor drainage, which can drastically increase wall loading.
- Soil Erosion at the Base or Top of the Wall: Washouts reduce toe support and may lead to base sliding or toppling of the wall.
- Cracking in Wall Structure: Horizontal, vertical, or diagonal cracks can point to shifting foundations, earth movement, or stress concentrations. These signs are often linked to both structural and geotechnical retaining wall failure types, highlighting deeper issues within the wall or supporting soil.
- Loss of Backfill or Sinkholes Near Wall: Pockets of missing soil indicate internal erosion, piping, or inadequate compaction.
- Movement of Adjacent Structures or Pavements: Nearby buildings or roads showing signs of shifting or settlement could be affected by the same soil instability affecting the wall.
- Rust Staining or Exposed Reinforcement: Signals corrosion of structural elements in reinforced concrete walls, weakening their integrity.
- Collapsed Drainage Outlets: Broken or blocked weep holes and pipes prevent proper water egress, leading to hydrostatic pressure buildup.
- Vegetation Changes (e.g., sudden die-off or lush growth): Unexpected plant changes may indicate hidden water accumulation or leakage behind the wall.
Main Causes of Retaining Wall Failures and Their Solutions
Here is a comprehensive list of common retaining wall failures and solutions to mend them:
Poor Drainage Behind the Wall
Cause:
Water accumulation behind the wall due to the absence of weep holes, improper grading, or impermeable barrier or membrane increases hydrostatic pressure, which the wall may not be designed to handle.
Solution:
- During retaining wall repair, install perforated drainage pipes (weeping tiles) behind the wall.
- Add gravel backfill and geotextile fabric to promote filtration.
- Ensure weep holes are regularly spaced and unobstructed.
Inadequate Wall Design (Structural and Geotechnical)
Cause:
Inadequate wall design is a leading cause of retaining wall failures. It occurs when structural or geotechnical factors are overlooked, such as wall height, soil pressure, seismic activity, surcharge loads, or water pressure. This leads to under-engineered walls lacking proper reinforcement, making them vulnerable to bending, tilting, or collapse.
Solution:
- Conduct a geotechnical site investigation before construction.
- Design walls using retaining wall design software or by consulting a structural engineer.
- Use proper reinforcement (e.g., geogrid for MSE walls, steel rebar for concrete walls).
- Consider external loads like vehicles or nearby structures.
Improper or Inadequate Backfill Material
Cause:
Using improper backfill materials like clay or expansive soils leads to poor drainage and increased hydrostatic pressure behind the wall. These soils retain water, swell when wet, and shrink when dry, causing movement and potential failure of the retaining wall.
Solution:
- Use granular material (gravel or crushed stone) for backfill.
- Compact soil in layers (lifts) during backfilling.
- Maintain proper slope to direct surface runoff away from the wall.
Foundation Settlement or Slope Movement
Cause:
Foundation settlement or slope movement occurs when weak, loose, or compressible soils beneath the wall can’t support the load, leading to uneven settling. This can cause cracking, tilting, or complete failure, especially on sloped sites or in unstable ground conditions.
Solution:
- Conduct a soil bearing capacity test before construction.
- Excavate and replace poor soils or use soil stabilization techniques like grouting, Deep Soil Mixing (DSM), Soil Nailing, etc.
- Use deep foundations (e.g., caissons, piles) if needed in weak soils.
- Install retaining wall footings below the frost line to prevent heaving.
Overloading or Improper Loading
Cause:
It happens when heavy structures, vehicles, or stockpiled materials are placed too close to the retaining wall. These surcharge loads increase lateral pressure beyond design limits, leading to wall tilting, cracking, sliding, or even complete falling.
Solution:
- Include expected surcharge loads in the design phase.
- Keep heavy loads away from the edge of the wall.
- Reinforce walls for higher loads or use tiebacks/anchors to help resist pressure.
Erosion at the Base or Behind the Wall
Cause:
Another top reason for retaining wall failure is erosion at the base or behind a retaining wall. This occurs when uncontrolled water flow washes away soil or backfill material. This weakens foundational support, leading to voids, settlement, and instability.
Solution:
- Install erosion control measures like riprap or turf reinforcement.
- Create graded slopes or retention swales to divert surface water during retaining wall repair.
- Apply vegetative cover or geotextiles to reduce surface erosion.
Poor Construction Practices
Cause:
Certain poor construction practices, such as inadequate soil compaction, rushed execution, or ignoring design specifications, compromise the wall’s integrity. These issues reduce stability, cause uneven settlement, and increase failure risk, even if the wall was well-designed on paper or in theory.
Solution:
- Follow engineered drawings for retaining wall design and functionality, and follow the specs strictly.
- Use experienced contractors for installation.
- Ensure on-site supervision and quality control testing during construction (e.g., compaction tests).
Material Degradation (Weathering, Rust, Rot)
Cause:
Another prominent retaining wall failure sign is material degradation. Weathering, rust, and rot occur when retaining wall components deteriorate over time due to exposure to environmental factors. For example, steel can corrode, timber can rot, and concrete can crack, weakening the structure’s ability to withstand loads.
Solution:
- Use weather-resistant materials (e.g., treated timber, concrete with additives, corrosion-resistant steel).
- Apply protective coatings (paint, sealants) on exposed surfaces.
- Schedule routine inspections and maintenance to detect early signs of wear.
Lack of Flexibility in the Wall Design
Cause:
Rigid wall designs, such as unreinforced masonry or concrete, lack the ability to flex under stress. Minor ground movements, seismic activity, or soil shifts can cause these walls to crack, leading to structural failure. Flexible designs prevent such damage by accommodating movement.
Solution:
- Use flexible systems like modular block walls with geogrid reinforcement.
- Incorporate expansion joints in long concrete walls.
- Design walls to tolerate movement from frost, seismic activity, or soil shifts.
Conclusion
A well-maintained retaining wall can protect your property for decades, but ignoring the signs and causes of retaining wall failures can lead to costly repairs. By understanding the common causes of failure and taking proactive steps, you can avoid major problems. If your retaining wall needs attention, reach out to My Landscape Contractor. Our expert team is here to help with repairs or new installations. Trust a seasoned retaining wall contractor to keep your property safe and secure!
