How does the maximum fill height under a slab differ when using gravel versus dirt/sand?

The correct response highlights that gravel allows for a greater maximum fill height compared to dirt or sand. This difference primarily stems from the physical properties and compaction characteristics of these materials.

Gravel has larger particle sizes and a more open structure, which allows for better drainage and reduces the likelihood of settling when loads are applied to a slab. This open structure enables air to escape more easily during compaction, resulting in a denser and more stable base. Therefore, when using gravel as a fill material, inspectors and builders can typically achieve a greater fill height without compromising the stability of the slab.

In contrast, dirt and sand tend to have finer particles and can compact more easily, which may lead to increased settling over time. This can limit the maximum fill height that is advisable for structural applications. Consequently, using gravel as a fill material is often preferred for scenarios needing a higher fill height and enhanced load-bearing capacity.