Which of the following is not generally a process used for compacting the pipe embedment and backfill placed in a trench?

The process of compacting pipe embedment and backfill in a trench is critical for ensuring the stability and longevity of the pipeline. Among the methods listed, sifting is not used to achieve compaction.

Sifting is generally a method used to separate materials based on size, such as removing large debris or aggregates from smaller particles. This process does not contribute to the density or stability required in compacting backfill.

In contrast, tampering, vibrating, and rolling are established methods for compacting materials. Tamping involves applying a force using a tamper to compress the soil, increasing its density. Vibrating uses vibrations to rearrange soil particles, which leads to better compaction and stability. Rolling utilizes a heavy roller to press down on the soil, which also aids in achieving the required compaction levels. Thus, among the standard methods for compacting backfill in a trench, sifting does not serve this purpose.