CSLB C-27 Landscaping ContractorHardscape and FeaturesHard
A homeowner wants a natural stone retaining wall that is dry-stacked (without mortar) to blend seamlessly with a rustic landscape. The wall will be approximately 3 feet high. Which design principle is most critical to ensure the long-term stability and integrity of a dry-stacked retaining wall of this height?
- AInstalling a geotextile fabric behind the entire wall face.
- BBackfilling with compacted, impermeable clay to prevent water intrusion.
- CEnsuring a batter (setback) of at least 1 inch per foot of wall height.
- DUsing only perfectly rectangular, cut stones for consistent courses.
Show answer & explanationAnswer & explanation
Correct answer: C. Ensuring a batter (setback) of at least 1 inch per foot of wall height.
A batter, or setback, where each course of stone is set back slightly from the course below, is absolutely critical for the stability of a dry-stacked retaining wall. This lean into the hillside uses gravity to counteract the lateral pressure of the soil, ensuring the wall remains stable without the need for mortar. A minimum of 1 inch per foot of height is a common guideline.
Why the other options are wrong
- A. A geotextile fabric is good for separating backfill, but it doesn't provide structural stability in the same way batter does for a dry-stacked wall.
- B. Backfilling with impermeable clay would trap water behind the wall, leading to immense hydrostatic pressure and almost certain failure, directly contrary to good practice.
- D. While consistent stones can aid construction, dry-stacked walls often use irregular stones; the key is interlocking, not perfect rectangles. This isn't the most critical stability factor.
Dry-Stacked Retaining Wall Batter
The intentional backward slope or setback of a dry-stacked retaining wall, where each course is set slightly behind the one below it.
- Essential for gravity-based stability.
- Counteracts lateral soil pressure.
- Typically 1 inch per foot of height or more.
Memory trick: A dry stone wall needs to LEAN IN, like a strong person against the wind, to hold its ground.