Final answer:
A mat foundation, also known as a raft foundation, is typically used for structures built on soil with poor load-bearing capacity, as it spreads the load over a larger area and provides a stable base even on weak soil conditions.
Step-by-step explanation:
When constructing a structure over soil with poor load-bearing capacity, engineers often use a mat foundation, also known as a raft foundation. This type of footing is designed to spread the weight of the building over a larger area, which reduces the stress on any one point.
The mat foundation generally covers the entire footprint of the structure, which helps to evenly distribute the structural loads to the underlying soil. It is particularly useful in situations where other types of footings, such as individual footings or strip footings, are not feasible due to the weak soil conditions.
Mat foundations are often constructed of reinforced concrete, providing a solid and stable base for the structure above. They are particularly beneficial in areas with expansive soils, high water tables, or where large, heavy structures are planned.
While the construction of a mat foundation can be more expensive and require more material, it is usually the best solution for ensuring the long-term stability of buildings on poor soils.