Retaining Walls That Fail: Avoid These Common Mistakes in Colorado
Retaining walls aren’t just decorative—they’re structural systems that hold back soil, control erosion, and protect your property. In Colorado, variable soil types, steep slopes, and freeze-thaw cycles make proper design and installation even more critical.
Many wall failures aren’t caused by the blocks themselves—they’re caused by improper site prep, poor material selection, or ignored soil conditions. Understanding the science behind retaining walls can save you thousands and prevent costly repairs.
1. Know Your Soil Type
Soil is the foundation of your wall, literally. Colorado soils vary widely:
Clay-heavy soils (common in Front Range suburbs): Expand when wet, contract when dry. Without proper reinforcement, walls can bulge or lean.
Sandy soils: Drain quickly but can shift under weight. Require proper compaction and geogrid reinforcement.
Rocky soils: Naturally stable, but irregular rocks can create voids behind walls, requiring careful backfill.
Tip: A soil test before construction informs wall design, drainage planning, and the type of reinforcement required. Using generic base instructions without considering soil can result in structural failure.
2. Proper Base Preparation
A stable base is the #1 factor for a wall that lasts. Skimping here is the fastest way to fail.
Steps for a durable base:
Excavation: Remove loose soil and organic material. Depth depends on wall height:
Short walls (under 4 ft): 6–12 inches below first course
Taller walls: Deeper, engineered base
Compacted Gravel Base:
Use ¾” to 1” crushed stone or gravel
Compact in 2–3 inch layers using a plate compactor
Ensure the first course of blocks sits level and square
Edge and Level Checks:
Small deviations in the first row can magnify up the wall.
Use a level and string line for alignment.
Colorado tip: In clay soils, extra base depth and compaction reduce frost heave during freeze-thaw cycles.
3. Reinforcement: Geogrid and Geotextile Fabric
Even with a solid base, soil behind the wall exerts lateral pressure. Reinforcement prevents leaning, bulging, and collapse.
Geogrid:
A synthetic mesh placed behind the wall in layers
Reinforces soil, distributes pressure, and stabilizes taller walls
Placement: Every 12–24” of wall height (depending on engineering and soil)
Geotextile Fabric:
Separates soil from drainage gravel to prevent clogging
Reduces erosion behind the wall
Ensures drainage systems work long-term
Tip: Proper integration of geogrid and geotextile fabric is essential for clay or sandy soils common in the Front Range.
4. Drainage: The Silent Wall Killer
Hydrostatic pressure (water build-up behind the wall) is the #1 cause of failure. Without proper drainage, even the strongest block system can fail.
Aggregate backfill: ¾” crushed stone behind the wall to facilitate water movement
Perforated drain pipe: Installed at base, sloped to direct water away
Surface grading: Grade soil above the wall away from the structure
French drains or swales: Useful on steep lots to reduce runoff
Colorado tip: Even modest rainfall can saturate clay soils, so drainage planning is critical.
5. Material Matters: Engineered vs. Natural
Choosing the right block system can make or break a wall:
Allan Block (engineered interlocking systems):
Interlocking blocks for stability
Designed for geogrid integration
Tested for lateral load capacity
Often allows taller walls without additional reinforcement
Natural stone:
Beautiful and durable
Requires precise installation, heavier wall footing, and often additional geogrid for stability
Less forgiving in clay soils
Concrete blocks:
Widely available, but quality varies
Avoid generic, non-engineered blocks—they may not hold up under lateral pressure
Tip: For walls over 4 feet, always use an engineered system with proper geogrid or hire a structural engineer.
6. Common Mistakes to Avoid
Skipping soil evaluation and base prep
Ignoring drainage or hydrostatic pressure
Using low-quality or non-engineered blocks
Forgetting geogrid or geotextile reinforcement
Building above recommended heights without permits or engineering
Result: Leaning walls, bulging walls, cracks, or complete failure.
Conclusion:
Retaining walls are both landscape and structural projects. Using proper soil evaluation, base prep, drainage, geogrid, geotextile fabric, and high-quality engineered blocks like Allan Block ensures your wall will stand the test of time.
Ready to build a retaining wall that’s engineered for Colorado soils and climate? Contact Terrain Bound Contracting for a consultation. We combine experience, engineering knowledge, and quality materials to keep your property safe, functional, and beautiful.
