Backfilling Trench Excavations: Progress Report 1962

Engineers who are associated with trenching in public thoroughfares have been striving for many years to find better construction methods and procedures for backfilling these trenches. We cannot expect the public to tolerate detrimental settlement if it can be avoided with a reasonable expenditure of funds.

In this study the presently used procedures of backfilling and compaction were observed. It was found that these procedures can definitely be improved. The major conclusions which can be drawn from the study are listed below.

The layered system is the most reliable compaction procedure for limiting settlement to a minimum. With one compactor type, the Hydra-Hammer, the entire trench backfill can be compacted in one lift irrespective of soil type or traffic volume on the street. Adequate stability, to prevent detrimental settlement, can be attained with many compactor types if the lift height is adjusted to soil type and condition, and the trench loading conditions. All vibratory type trench compactors should be used strictly on the granular soils and the lift height must be chosen with respect to the particular compactor and the traffic volume. The Pneumatic Button Head compactor can effectively compact all soil types in lifts up to 0.5 feet in thickness. The Plate Tampers are excellent compactors for all soil types and they are capable of compacting soil lifts between 1.0 and 1.5 feet depending upon the traffic load. Heavy construction equipment should be used to compact only the upper lift in a trench and this lift should be restricted to the range of 1.0 to 2.5 feet in thickness depending upon the soil type and the traffic load.

Further research under more controlled field conditions is planned for 1963.