Field Study on Characterizing the Backfill Materials Around Water Pipelines

The density of the backfill material around flexible water pipe is an important quality control measurement to ensure support for the pipeline. If the backfill material is not properly placed at the recommended density, then it could not only affect the long-term performance of the pipe, but also damage the infrastructure around it. Field tests were undertaken at different locations to determine the in-situ density of backfill extending 30 inches (762 mm) in diameter around a water pipeline. The field methods included Shelby tube sampling, direct push method and nuclear gage method. Repeatability of the test methods was also investigated. Using the direct push method, the spatial variation in density and moisture content of backfill material around the pipe were measured. Results from the in-situ tests were compared to the density specified in the design, based on laboratory compaction testing.