Evaluating the Compaction Quality of Backfills by Stress Wave Velocities

In engineering practices, sand-cone tests are usually performed to assess the compaction quality of backfilled materials of highway embankments or earth dams. However, performing the sand-cone test is time consuming and can only obtain the physical but not the engineering properties of backfills. The objective of this paper is to investigate the feasibility of evaluating the compaction quality of backfills using stress wave propagation velocities. To achieve this goal, a backfill material with low plasticity used in the earth dam of the Hushan Reservoir in Taiwan was collected and tested. The calibration curves for the relationship among moisture content, dry density, and stress wave velocities were obtained. In order to verify the validity of the laboratory calibration curves, field tests were also performed on a trial embankment at the site of the reservoir. Comparing with values measured in the field using the traditional sand-cone test, the proposed method underestimates the water content and overestimates the dry density of the compacted backfills. The resulting error is less than 10 %. It is thus concluded that the proposed method is a promising tool for the evaluation of the compaction quality of backfills.