EVALUATING THE METHODOLOGY AND PERFORMANCE OF

Abstract

Compaction of backfill in confined spaces on highway projects is often performed with small vibratory plates, based solely on the experience of the contractor, leading to inadequate compaction. As a result, the backfill is prone to erosion and often exhibits excessive settlements, causing loss of support beneath pavements. The scope of this project includes developing standard specifications for two alternative hydraulic compaction methods, flooding and jetting, which additionally are suitable in confined spaces. During flooding, or compaction by drainage, the backfill layer is saturated with water from the surface and allowed to drain. During jetting, a probe emitting a high pressure jet of water is inserted into the layer, and the backfill is allowed to drain. In both cases the energy of the flowing water and residual suction upon drainage increase the effective stress and move the grains into a denser arrangement. The results in the lab indicate that for compaction by drainage applications, uniform, rounded soils achieve the highest relative density due to their minimal particle interlocking upon deposition and subsequent high drainage capacity. Meanwhile during jetting applications, soils liquefy locally around the jet of water, and their compactness upon drainage is highly dependent on the hydraulic gradient, or the energy with which water drains from the pore space. Greater hydraulic gradient during the drainage phase of jetting has been observed to produce more compact soil structure.