Working with Clay Soils

Townelake development overcomes challenging clay soils with engineered retaining walls, allowing 225 homes to be built successfully.

Townelake Development Thrives Despite Challenging Soil Conditions

The Townelake development offered tremendous benefits to homeowners. Its prime location near the Garden State Parkway and multiple major commuting routes, as well as bus and train lines, made it a commuter’s dream. However, the site itself posed significant challenges that needed to be addressed before construction could proceed.

Overcoming Clay Soil Challenges

The site previously housed the Sayre & Fisher Brick Company, which manufactured clay bricks using the local clay deposits. These soils created difficulties for development, as the existing slopes were already unstable. Despite this, the developer, Kaplan Companies, recognized the value of the site and enlisted a team of professionals to make it work.

Local engineer Converse Consultants and AB Master Wall Builder Earth Management collaborated to adapt design and construction methods to the challenging soils and slopes.

• Eastern portion: Clay soils were unsuitable for retaining wall construction, so select engineered backfill was brought in to replace them.
• Other areas: Clay could be used as backfill, but longer and higher-strength geogrid layers were required to accommodate the additional lateral pressure.
• Northern terraces: Terraced retaining walls stabilized slopes and ensured global stability. Large shot-rock material from a local quarry was placed beneath the walls to prevent future landslides.
• Water management: Chimney and blanket drains were installed in the walls to handle elevated groundwater, while final grading ensured proper water diversion and collection.

Through proper design and construction of over 60,000 square feet of Allan Block retaining walls using the AB Stones product from Clayton Block, 225 Colonial-style single-family homes were successfully built. A second phase is underway with an additional 30,000 square feet of retaining walls, demonstrating that with the right plan, even challenging sites can succeed.

Identifying Clay Soils

Understanding the soil conditions is critical when designing or building retaining walls. Expansive clay soils can cause significant challenges because they change volume with moisture fluctuations:

• Wet seasons: Clay expands.
• Dry seasons: Clay shrinks.

Rigid structures like cast-in-place or masonry walls may crack under these conditions, whereas Allan Block retaining walls offer flexibility that helps accommodate movement.

Atterberg Limits

To assess clay behavior, soils are tested for their Atterberg Limits, which measure plasticity:

• Plastic Limit (PL): Water content at which clay starts to behave like plastic rather than solid.
• Liquid Limit (LL): Water content at which clay behaves more like a liquid than plastic.
• Plasticity Index (PI = LL – PL): Indicates expansion potential. Clays with PI ≥ 50 (“fat clays”) are highly expansive and problematic behind retaining walls.

Allan Block recommends avoiding soils with PI > 20 or LL > 40 for wall construction.

Working with Expansive Clays

Expansive clays exert high lateral pressures on retaining walls and should be managed carefully. Options include:

1. Chemical treatments: Lime, silica fume, fly ash, polymers, acids, or emulsions can reduce expansion potential (testing required).
2. Pre-wetting: Moistening clay before construction to induce pre-expansion, reducing future pressure.
3. Removal and replacement: Most common method, replacing clay with select engineered backfill that drains water and buffers the wall from expansive soils.

Proper Compaction

Moisture content is critical. Expansive soils compacted at or slightly above optimum moisture levels (per AASHTO T99 and ASTM D698) absorb less water and achieve higher strength.

Right equipment matters:

• Granular soils: Use vibratory plate compactors for effective compaction.
• Cohesive/expansive clays: Use high-impact equipment like a pad-foot vibratory roller for proper compaction without disturbing wall placement.

Allan Block recommends using the vibratory plate compactor on top of walls and granular backfill, switching to pad-foot rollers when compacting clay backfill.

With thoughtful design, proper materials, and careful construction, even challenging clay soils can be managed effectively—just as demonstrated at the Townelake development.