In which type of foundations, the length is considerably greater than its width?
🔬 Understanding Foundation Types by Geometry
Foundations are the structural elements that transfer the load of a building safely to the ground. They can be classified in many ways, one of which is by their shape and geometry in plan view. The question asks to identify the foundation type that is long and narrow.
⚖️ Detailed Analysis of the Options
Let's evaluate each foundation type based on the description.
(d) Strip foundation
Why it's correct: A strip foundation, also known as a continuous footing, is a long, narrow strip of concrete that runs under the entire length of a load-bearing wall. Its purpose is to distribute the linear load from the wall over a wider area of soil. By its very definition, its length is considerably greater than its width. This is the correct answer.
(a) Footing
Why it's incorrect: "Footing" is a general term for the part of the foundation that is in direct contact with the soil. A strip foundation is a type of footing, but so is an isolated pad footing (which is square or rectangular). The term is too general.
(b) Pile foundation
Why it's incorrect: A pile foundation is a deep foundation system. It consists of long, slender vertical columns (piles) that transfer load to deep soil strata. The question is describing the plan dimensions (length and width) of a shallow foundation, not the vertical dimension of a deep foundation element.
(c) Raft foundation
Why it's incorrect: A raft (or mat) foundation is a large, single slab of concrete that covers the entire footprint of the building. It is used when column loads are heavy or the soil is weak. Its length and width are of a similar order of magnitude; its length is not "considerably greater" than its width.
📋 Other Foundation Definitions
- Shallow Foundation: A foundation where the depth is less than or equal to its width. Strip and raft foundations are types of shallow foundations.
- Deep Foundation: A foundation where the depth is much greater than its width. Pile foundations are a type of deep foundation.
- Combined Footing: A footing that supports two or more columns. It is essentially a small mat foundation.