Building Retaining Walls in Sand: Geotech Report Required

Landscape contractor plans two 80-ft × 4-ft walls in sand (staggered, with stairs). Used to clay. Asks about footing depth, rebar, settlement risk.

Sand Requires Engineering

Sand varies wildly (loose to dense, clean to silty). Never guess. Hire a geotechnical engineer for:

• Borings along alignment (1–2 per 100 ft).
• Bearing capacity (target ≥ 3,000 psf).
• Settlement analysis.
• Seismic/liquefaction check if applicable.

Typical Outcomes

• Dense, clean sand: Standard footing (24" wide, 12" thick) on compacted native may work.
• Loose/silty sand: Overexcavate 2–3 ft, replace with compacted structural fill, or widen footing.
• Poor sand: Deep foundations (helical piers, driven piles) needed.

Cost Reality

• Geotech report: $500–$2,000.
• Engineer-stamped wall design: $1,500+.
• Your 1-year warranty is meaningless if the wall fails from inadequate design.

Do it right. The engineer's fee is insurance against a $50k+ failure.

Expert: Sean Murphy, LA, ISA, LEED AP | www.seanjmurphy.com