NASCLA Accredited Commercial General ContractorSite WorkEasy
A contractor is preparing a site for a new commercial building. The geotechnical report indicates the presence of highly expansive clay soils. Which of the following foundation types is generally most suitable for mitigating the risks associated with such soil conditions?
- ASpread footing foundation
- BContinuous wall footing
- CSlab-on-grade foundation
- DPier and beam foundation
Show answer & explanationAnswer & explanation
Correct answer: D. Pier and beam foundation
Expansive clay soils are prone to significant volume changes due to moisture fluctuations, which can cause differential settlement and damage to structures. A pier and beam foundation elevates the structure above the expansive soil, isolating it from these movements.
Why the other options are wrong
- A. Spread footings are susceptible to movement and damage from expansive soils.
- B. Continuous wall footings, similar to spread footings, are vulnerable to damage from expansive soil movements.
- C. Slab-on-grade foundations are directly affected by the swelling and shrinking of expansive soils.
Pier and Beam Foundation
A foundation system consisting of concrete piers or piles extending into stable soil, supporting a framework of beams on which the structure rests.
- Elevates the structure above ground.
- Minimizes contact with expansive or unstable soils.
- Commonly used in areas with clay soils or flood risks.
Memory trick: Piers Elevate, Beams Support, Expansive Soils Don't Touch.