Development of a Laboratory Rotary Compactor and a Miniature Cone for the Quality Control of Backfills

The Proctor test has been performed in conjunction with the field sand cone test for the quality control of earthworks for decades. However, the way that compaction energy is applied in a Proctor test (drop weight) is different from most of the field compactors (rotary/vibratory). The compaction characteristics, such as maximum dry density and optimum moisture content (OMC), are very likely to vary with compaction methods. Furthermore, performing a sand cone test is time consuming and can only obtain the physical properties (such as density and water content) rather than the engineering properties (such as bearing capacity or strength) of backfills. The objective of this study is to bridge the gap between the difference in laboratory and field compaction and to develop a quick and economic method for the quality control of backfills. To achieve this goal, a rotary compactor and a miniature dynamic cone penetrometer were developed. Samples of a silty clay were compacted using the rotary compactor at various moisture contents. In addition to the dry density, the California bearing ratio (CBR), stress wave velocity, as well as penetration resistance of the miniature cone of these samples were measured. It was found that the OMCs obtained from rotary compaction are higher than values obtained from Proctor compaction. Linear relationships between the CBR and stress wave velocities with dynamic cone penetration resistance were also found.