What should be used when backfilling a trench if proper compaction is difficult?

When backfilling a trench where achieving proper compaction is challenging, using a mixture of gravel, soil stabilizer, or slurry is advisable. This option is beneficial because these materials enhance the stability and load-bearing capacity of the backfill.

Gravel provides good drainage and reduces the likelihood of settling, while soil stabilizers help bind the soil particles together, preventing erosion and maintaining the integrity of the backfill over time. Slurry mixtures can fill voids and provide additional density, which is particularly useful in areas where standard compaction methods may not be feasible.

This combination of materials ensures that the backfill will settle uniformly and maintain stability, significantly reducing potential problems like sinkholes or structural issues that could arise from improper compaction. Using packed clay, a sand mixture, or loose soil would not provide the same level of stability and could lead to inadequate support for the structures above.