Retaining Walls—The Underestimated Structural Threat

Understanding the Forces at Work

Retaining walls serve to separate different ground elevations in terrain that naturally tends toward slopes. The earth constantly exerts pressure against these structures, attempting to return the soil to its natural sloping state. This creates a continuous natural force pressing against the wall, trying to restore the landscape to its intended configuration.

The lateral forces from earth and water can be enormous, making proper engineering design essential to prevent the wall from overturning or sliding. Groundwater accumulation behind retaining walls presents an additional significant challenge.

Without adequate drainage systems to dissipate water and reduce hydrostatic pressure, the stability of the material behind the wall becomes severely compromised.

An effective drainage system is vital to improving the wall's overall stability. Traditional dry-stone walls typically provide natural self-drainage through their construction method.

The Insurance Challenge

Insurance providers approach retaining walls with considerable caution. When cover is offered, it typically comes with substantial premium surcharges and extensive policy exclusions. Insurers commonly require a stability report before agreeing to provide cover.

The stability report process involves exposing the foundation at multiple locations so a qualified structural engineer can thoroughly assess the wall's integrity. This allows the engineer to examine the wall's structural soundness and determine whether it can withstand the forces acting upon it.

While the combined cost of engineering assessment and excavation work may seem prohibitive to many property owners, it's important to consider the full picture.

Regular maintenance to extend a retaining wall's lifespan is also expensive and ongoing.

Eventually, every retaining wall reaches the end of its serviceable life and must be replaced.

More importantly, the potential financial consequences of a failing retaining wall should never be underestimated. A collapsed retaining wall can cause catastrophic damage to structures, landscaping, and adjacent properties, with repair costs far exceeding the

investment in proper assessment and maintenance.

Interlocking Block Walls

Retaining walls constructed from loosely stacked, interlocking concrete blocks present heightened risks due to their construction method. Because of the nature of their assembly and the inherently higher claim frequency associated with these structures, most, if not all, insurance providers consider them uninsurable.

The Hidden Retaining Wall Problem

A particularly common and dangerous scenario involves boundary walls unknowingly assuming retaining wall duties. This occurs when soil levels rise on one side of an existing boundary wall due to:

• Landscaping modifications

• Adjacent property development

• Natural soil movement and erosion patterns

What begins as a simple boundary wall suddenly faces forces it was never designed to withstand. In many cases, ownership of and responsibility for dividing walls remains unclear to property owners until after damage has occurred, either to the wall itself or to the lower-situated property.

This ambiguity can lead to disputes between neighbors about who bears responsibility for repairs or replacement, especially when the damage results from actions taken on one property that affected a shared wall.

Critical Warning Signs

Maintaining awareness of conditions on both sides of the walls at all times is important. Impending retaining wall failure typically presents obvious warning signs that should never be ignored:

• Crumbling mortar - Deterioration of the bonding material between blocks or stones

• Cracking joints - Visible cracks appearing in mortar joints or through structural elements

• Outward bowing - The wall beginning to lean or bulge outward under pressure

• Drainage issues - Water pooling behind the wall or seeping through it

• Settlement or tilting - The wall shifting from its original vertical position

• Separation from adjacent structures - Gaps forming between the wall and structures it connects to

Addressing Deterioration

While these deterioration signs can be addressed through targeted repairs in early stages, property owners must understand that these are typically temporary solutions.

The most economical long-term solution usually involves:

1. Complete demolition of the failing structure

2. Proper engineering design based on the specific site conditions, including:

   • Soil composition and properties

   • Water table levels and drainage patterns

   • Height and load requirements

   • Adjacent structure considerations

3. Reconstruction according to engineering specifications

4. Installation of adequate drainage systems

5. Use of appropriate materials for the environment

Properly engineered and constructed retaining walls become insurable structures,

whereas deteriorating or improperly built walls often cannot obtain cover.

Proactive Assessment

Property owners, managers and Trustees should consider professional assessment of their retaining walls, particularly:

• Walls showing any of the warning signs listed above

• Walls of unknown age or construction method

• Walls that may have become retaining walls due to changed soil levels

• Walls constructed from interlocking blocks

• Walls without visible drainage systems

• Walls that will be crucial to the property's stability and value

Some property valuation professionals offer to examine retaining walls during standard property assessments and include observations in their reports at no additional charge.

This can provide valuable early warning of potential issues before they become emergencies.

Retaining walls represent a significant structural responsibility that should never be taken lightly. The forces acting on these structures are relentless and powerful. While the costs of proper engineering assessment, maintenance, and eventual replacement may seem substantial, they pale in comparison to the potential damage from a catastrophic failure.

Property managers and Trustees should adopt a proactive approach: regularly inspect retaining walls, address warning signs promptly, maintain proper drainage, and consult qualified engineers when concerns arise. Understanding the physics and risks involved with retaining walls can help prevent disasters and protect both property values and personal safety.

Remember: a retaining wall is not just a landscaping feature, it's a critical structural element holding back tremendous natural forces. Treat it with the respect and attention it deserves.