What is a key feature of a raft slab foundation?

A raft slab foundation, also known as a mat foundation, is characterized by the use of mat reinforcing bars, which are positioned in two directions, typically in both the lateral and longitudinal directions. This reinforcement is crucial because it helps to distribute the load from the structure evenly across the slab and enhances its structural integrity. The two-way reinforcement is essential for handling various stresses that may be applied to the slab, especially in scenarios where the foundation must support a heavy load or is situated on less stable soil.

In contrast, options suggesting that a raft foundation does not require reinforcement, consists only of a single layer of concrete, or requires no subgrade preparation reflect inaccurate or incomplete characteristics of this type of foundation. Reinforcement is fundamental to ensuring that the raft slab can withstand loads effectively, while proper preparation of the subgrade is also critical for providing a stable base and preventing any settlements or heaving that could compromise the foundation's performance.