CSLB General Building (B)Site Work, Foundations and ConcreteHard
A soils report for a site with highly expansive clay recommends supporting the foundation walls on a system of drilled concrete piers connected by reinforced horizontal concrete beams that span between the piers, keeping the structure elevated above the expansive soil. What is this structural element called?
- AA stem wall
- BA spread footing
- CA grade beam
- DA slab-on-grade
Show answer & explanationAnswer & explanation
Correct answer: C. A grade beam
A grade beam is a reinforced concrete beam that transfers structural loads from walls to isolated foundation supports such as piers or caissons. It is commonly used on expansive soils to span between deep piers, minimizing direct contact between the structure and soil that could heave or shrink.
Why the other options are wrong
- A. A stem wall extends from a footing to support a wall but doesn't span between deep piers.
- B. Spread footings bear directly on soil, which is what this system is designed to avoid.
- D. A slab-on-grade rests directly on the ground and would be vulnerable to expansive soil movement.
Grade Beam
A reinforced concrete beam that spans between deep foundation supports (like piers or caissons) to carry structural loads while minimizing contact with unstable or expansive soils.
- Commonly used with pier-and-beam foundations
- Reduces direct soil contact on expansive clay sites
- Transfers loads to deep, stable bearing points
Memory trick: A grade beam bridges the gap so the building floats above the moving clay.