A proposed residence is on verified expansive soil. Which response best addresses the foundation risk?
Correct Answer
A) Obtain soil data and a foundation design for the expected movement
Expansive soils can shrink or swell as moisture changes. Appropriate geotechnical information and an engineered design addressing the actual soil conditions are needed; neither a foundation label nor elevation alone guarantees performance. FEMA lists multiple possible mitigation methods.
Why This Is the Correct Answer
Option A is correct because expansive soils can shrink or swell as moisture changes, so the foundation must be designed for the actual soil conditions. Obtaining soil data and an engineered foundation design for the expected movement addresses that risk directly. In areas likely to have expansive soil, building officials can require soil tests to determine where such soils exist.
Why the Other Options Are Wrong
Option B: Prohibit basements on expansive-soil sites in the subdivision
Option B, prohibiting basements on expansive-soil sites in the subdivision, is a blanket rule that does not address the actual soil conditions at this site. Proper response depends on soil data and engineered design, not on banning one foundation type.
Option C: Assume any ordinary slab foundation is immune to soil movement
Option C assumes any ordinary slab foundation is immune to soil movement. Slabs on expansive soil can be affected by shrinking and swelling unless designed for it.
Option D: Assume a crawl-space design provides stable bearing for the house
Option D assumes a crawl-space design provides stable bearing for the house. A foundation label or elevation alone does not ensure performance on expansive soil without engineering for the expected movement.
Test the soil, then design
For soil that swells and shrinks, test first and design second. No foundation type is safe by label alone.
How to use: Use this sequence when a question involves problem soils and foundation choices.
Exam Tip
Favor answers that call for site-specific data and engineered design over answers that assume a foundation type will perform well.
Common Mistakes to Avoid
- -Assuming a slab foundation resists soil movement without engineering
- -Thinking a crawl space alone solves expansive soil problems
- -Applying a blanket rule instead of site-specific analysis
Concept Deep Dive
Analysis
This question tests the appropriate response to verified expansive soil, which can shrink or swell as moisture changes. The sound approach is to obtain geotechnical data and an engineered foundation design for the expected movement. Options that assume a foundation type will perform well, or that impose an unrelated blanket rule, do not address the actual soil conditions.
Background Knowledge
Expansive clay soils change volume with moisture, which can crack foundations, slabs and walls. Geotechnical investigation identifies the soil and its expected movement, and engineers design foundations to accommodate it. Several mitigation methods exist, and the right one depends on site conditions.
Real-World Application
An appraiser is asked to value a proposed home in an area known for expansive clay. She requests the geotechnical report and engineered foundation plans, and makes her appraisal subject to completion per those plans.
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