CSLB C-27 Landscaping ContractorHardscape and FeaturesMedium
A client requests a retaining wall to hold back a 4-foot soil bank. The local building code requires a permit for walls exceeding 3 feet in height. What is the most critical factor to consider when designing the footing for this retaining wall?
- AThe availability of local aggregates for concrete mix.
- BThe aesthetic finish of the visible wall face.
- CThe depth of the frost line in the project's geographic area.
- DThe type of backfill material to be used behind the wall.
Show answer & explanationAnswer & explanation
Correct answer: C. The depth of the frost line in the project's geographic area.
The depth of the frost line is a critical factor for any structural footing, including retaining walls. If the footing is not placed below the frost line, repeated freeze-thaw cycles can cause frost heave, leading to cracking, shifting, and structural failure of the wall.
Why the other options are wrong
- A. Availability of aggregates affects cost and logistics but not the engineering requirement for footing depth.
- B. Aesthetic finish is important for appearance but does not affect the structural integrity of the footing.
- D. Backfill material affects lateral pressure on the wall but is not the most critical factor for footing design itself.
Retaining Wall Footing Depth
The vertical distance from finished grade to the bottom of a retaining wall's foundation.
- Must be below the frost line in cold climates.
- Ensures stability against frost heave.
- Distributes the wall's load to the soil.
Memory trick: A strong wall needs a DEEP, FROST-FREE foundation to stand tall.