Effects of Lift Thickness, Backfill Material, and Compaction Energy on Utility Trench Backfill Compaction Using Hydraulic Plate Compactors

Excavator-mounted hydraulic plate compactors have been used extensively for utility trench backfill compaction due to their efficiency. However, there is a need to study their effect on compaction and pipe performance in terms of loose lift thickness, backfill material, and compaction energy due to the lack of well-documented field studies. This paper presents the results of a field investigation to serve this need. Three different excavator-mounted hydraulic plate compactors with different compaction energy levels were used to compact two backfill soils: a well-graded 2A aggregate soil (gravel with sand), and a well-graded wash sand (sand with gravel). Three different loose lift thicknesses were used: 300, 450, and 600 mm (12, 18, and $24\mathrm{in.}$). The results showed that the compacted dry density achieved in the field was dependent on the loose lift thickness, impulse force of the compactor, and the backfill material used. High-energy compactors effectively achieved high dry densities in the field for the 2A aggregates even at $600\text{-}\mathrm{mm}$ lift thickness, whereas for the wash sand, they over-compacted the backfill, leading to lower densities. In contrast, low-energy compactors were effective in compacting the wash sand, achieving the target dry densities at $600\text{-}\mathrm{mm}$ lift thickness. The high-energy compactors resulted in high compaction-induced stresses in the backfill; however, compaction-induced strains in the pipes generally were similar irrespective of the compactor used.