Final answer:
Trenches should not be backfilled with rocks and debris as it can leave voids; instead, finer soil compacted in layers should be used to provide stability.
Step-by-step explanation:
Trenches should generally not be backfilled with rocks and debris because this material can leave voids or spaces that do not provide adequate support for the trench walls or the surface above the trench. Instead, backfilling should be done with appropriate materials and in layers, compacting each layer thoroughly to ensure stability and prevent future settling or collapse. Backfill material should be chosen based on the engineering requirements and the purpose of the trench, and often consist of finer soil that can be compacted to achieve the necessary density for support.