Effect of Hydraulic Plate Compactor and Lift Thickness on Utility Trench Backfill Compaction

Open Access
Wang, Chaoyi
Graduate Program:
Civil Engineering
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 27, 2015
Committee Members:
  • Tong Qiu, Thesis Advisor
  • Compaction
  • Pipe
  • Hoe-pack
  • Soil
For utility trench backfill compaction, compaction-induced earth pressure in the backfill zone and deformation along the pipe are two important issues to be addressed. Backfill materials should be adequately compacted to lock the pipe in place and reduce potential settlement from external loading (e.g., traffic loading). On the other hand, excessive backfill compaction from compaction equipment may damage the pipe. Backhoe-mounted hydraulic plate compactors (hoe-packs) have been increasingly used for soil compaction in trenching, street repairing, or site preparations. Comparing to traditional compaction tools such as roller compactors, hoe-packs are advantageous for utility trench backfill compaction as they can be operated by the backhoe operator and requires no lifting of compaction machine during compaction process. However, uncertainty remains with regard to the maximum lift thickness to consistently achieve desired compacted dry mass density by hydraulic plate compactors. The large impulse energy and down pressure exerted by hydraulic plate compactors also raise concerns on potential damages to utility pipes. The objective of this study is to assess the capability of a hoe-pack for utility trench backfill compaction. Field tests were conducted to investigate the effect of hoe-pack on compacted dry mass density, compaction-induced earth pressures, and compaction-induced strains in pipe. Different values of lift thickness and pipe materials were used. Compaction tests using hand-held vibratory roller compactors which followed the specifications of the Pennsylvania Department of Transportation (PennDOT) were conducted as a control set. It is concluded that the hoe-pack used in this study can consistently achieve relative densities above 100% of the Standard Proctor Density (SPD) with a lift thickness of 8 inches or 12 inches. However, the hoe-pack is not able to consistently achieve relative densities above 100% of SPD 12 inches below the compacted surface when the lift thickness is 18 inches or greater. Comparing the performances of the hoe-pack and vibratory roller compactor used in this study for a lift thickness of 8 inches, the hoe-pack is more efficient in performing compaction. The hoe-pack used in this study is likely to induce higher dynamic earth pressures in the backfill zone, but may not induce higher static earth pressures depending on the pipe material and diameter. The hoe-pack used in this study generally induces similar strains along pipe as the vibratory roller compactor does. For the hoe-pack used in this study, the static earth pressures in the backfill zone are relatively insensitive to lift thickness, whereas the dynamic earth pressures may decrease as the lift thickness increases, depending on the pipe. The effect of lift thickness on strains developed along pipe also depends on the pipe.