What should the backfill material for a pipe installation contain to ensure proper compaction?

The inclusion of moisture in backfill material is essential for achieving proper compaction when installing pipes. When backfill is moist, it aids in the cohesion of the soil particles, allowing them to bond more effectively when compacted. This moisture activates the soil's compaction characteristics, ensuring that air pockets are minimized and creating a denser fill. Proper compaction is crucial for providing the necessary support to the pipe, preventing it from shifting and maintaining the stability of the installation.

In contrast, while materials like sand or rocks might be used in backfill, they do not necessarily guarantee proper compaction. Sand, for example, tends to have less cohesion without the presence of moisture. Similarly, adding extra rocks can create voids and hinder the compaction process. Filler material may also help, but it does not directly address the compaction issue without the appropriate moisture content. Therefore, ensuring that the backfill material contains moisture is the key factor for achieving the desired compaction and overall stability of the pipe installation.