For backfill in trenches through cohesive materials, what is the required maximum compaction density?

For backfill in trenches through cohesive materials, the required maximum compaction density is crucial in ensuring the structural integrity and stability of the backfill material. A compaction density of 95% relative density is typically specified due to the following reasons:

Cohesive soils, such as clay, require a higher level of compaction to minimize settlement and prevent issues such as water accumulation, which can lead to erosion or weakening of the material over time. Achieving a compaction density of 95% helps to ensure that the backfill material has reduced air voids, leading to improved load-bearing capacity and enhanced overall stability.

This level of compaction also contributes to the effective prevention of excessive post-construction settlement, which can be particularly important in areas with varying moisture levels that could affect the expansion and contraction of the cohesive material.

In contrast, lower compaction densities, such as 85% or 90%, may not provide the necessary strength and stability needed for cohesive materials, potentially exposing the construction to risks associated with shifting or settling over time. A compaction density of 100% is typically not practical in field conditions due to limitations in achieving absolute maximum density and can lead to excessive effort and cost without significant gains in performance. Thus,