Which method is recommended for correcting over-excavation of a trench before laying pipe?

Using sand or fine gravel, compacted to a maximum depth of 6 inches, is the recommended method for correcting over-excavation of a trench before laying pipe because it effectively provides a stable and supportive base. This method ensures that the surrounding soil retains proper drainage characteristics while also distributing load evenly around the pipe.

Compacted sand or fine gravel helps to minimize settlement and instability that might arise if the trench were filled with unsuitable materials or allowed to remain unfilled. The use of a maximum of 6 inches ensures that the material does not shift excessively, contributing to the structural integrity of the installation.

In contrast, using gravel only might not provide the same level of compaction needed for optimal support. Concrete filling, while sturdy, could lead to complications with drainage and flexibility, which are crucial in plumbing applications. Soil replacement may not achieve adequate compaction unless done with great care and consideration, as loosely placed soil can easily lead to shifting and settling. Therefore, the choice of sand or fine gravel, with careful compaction, presents the most effective solution.