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 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-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-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.