Foundation types – grillage foundation basics: Which statements correctly describe a grillage foundation used under heavy isolated columns?

Introduction / Context:
Where soil near the surface has adequate bearing capacity but a pedestal footing would be too thick or inefficient, a grillage foundation provides economical load spreading for heavy columns, chimneys, or stanchions. It is widely used in steel construction and retrofits where shallow depth is preferred.

Given Data / Assumptions:

• Loads are predominantly vertical from isolated columns.
• Sufficient space exists to spread loads through multiple beam layers.
• Corrosion protection and concrete encasement are provided in practice.

Concept / Approach:
A grillage is a spread foundation comprised of orthogonal layers of beams (steel or treated timber) embedded in concrete to distribute concentrated column loads over a wider area, reducing contact pressure on the soil. It is categorized under shallow foundations and designed to maintain acceptable settlement and bearing stresses.

Step-by-Step Solution:

Verification / Alternative check:
Design guides show bearing pressure checks, beam bending and shear, and spacing to ensure concrete infill transfer and ease of placement.

Why Other Options Are Wrong:

• “None” contradicts standard practice descriptions; A–C are accurate.

Common Pitfalls:
Ignoring corrosion protection for steel grillages; inadequate concrete cover; neglecting settlement compatibility when multiple columns are supported.

Final Answer:
All of the above