Understanding different types of foundations is crucial in civil engineering. Foundations transfer the load of a structure to the underlying soil or rock. They are broadly classified into two main categories: shallow foundations and deep foundations.

Shallow Foundations Explained

Shallow foundations are used when the soil near the ground surface has sufficient bearing capacity to support the structural loads. These foundations transfer the load at a shallow depth, generally less than or equal to the width of the foundation, or less than 3 meters (10 feet). Common types of shallow foundations include:

• Isolated Footings: These are pads that support individual columns. They can be square, rectangular, or circular.
• Wall Footings (or Strip Footings): These are continuous footings that support load-bearing walls.
• Combined Footings: These support two or more columns.
• Mat or Raft Foundations: These are large slabs covering the entire area beneath the structure, supporting multiple columns and walls.
• Grillage Footings: These consist of two or more tiers of steel beams or reinforced concrete beams laid at right angles to each other, used to distribute heavy loads from columns over a wider area, often at shallow depths.

Based on this, Isolated footing, Wall footing, and Grillage footing are all examples of shallow foundations.

Deep Foundations Explained

Deep foundations are used when the soil near the surface is weak or compressible, and the required bearing stratum is located at a significant depth. These foundations transfer the load to deeper, stronger soil layers or bedrock through skin friction along the shaft and/or end bearing at the base. Examples include piles, piers, and caissons.

Open Caissoons vs. Shallow Foundations

Open caissons (also known as well foundations) are a type of deep foundation. They are large, hollow structures (often concrete or steel) that are sunk into the ground to the desired depth. The soil inside the caisson is excavated as it sinks. Once the required depth is reached, the base is usually sealed with concrete, and the rest of the caisson is filled, often with concrete or sand, to form a solid foundation element.

Since Open Caissoons extend deep into the ground to reach suitable bearing strata, they are classified as deep foundations, not shallow foundations.

Conclusion on Shallow Foundation Examples

Among the options provided:

• Grillage footing: A type of shallow foundation.
• Wall footing: A type of shallow foundation.
• Open Caissoons: A type of deep foundation (Caisson).
• Isolated footing: A type of shallow foundation.

Therefore, Open Caissoons is the example that is not a shallow foundation.