Feasability of using a gyratory compactor to determine compaction characteristics of soil

Abstract

Proctor impact compaction tests represent the most commonly used laboratory method to determine the maximum dry unit weight and optimum moisture content of soils in the United States. Soil compaction methods in the field have changed dramatically over the last 50 years, though the Proctor tests have remained relatively unchanged. One shortcoming of the Proctor tests is that it uses impact loads to compact the soil in a stiff non-yielding mold. This technique may not accurately simulate modern field compaction methods, which rely on a combination of kneading, vibration, and increased normal pressures to achieve high dry unit weights. Consequently, a more appropriate method of compacting soils in the laboratory is needed. The research presented herein explores the feasibility of using a Superpave Gyratory Compactor (SGC) to compact soil specimens. The SGC was created in the early 1990s to accurately represent in-place asphalt densities. Gyratory compactors simultaneously use static compression and a shearing/kneading action to compact asphalt mixtures. Variables within gyratory compaction (confinement pressure, number of gyrations, soil type, and moisture content) were explored to determine their effects on soil compaction.

Gyratory compaction results, expressed in terms of dry unit weight and optimum moisture content, were compared to traditional laboratory compaction methods (Proctor and relative density tests). These results indicated that each soil type (A-1-a, A- 3, A-4, and A-7-6) was sensitive to one or more of the gyratory compaction variables. When compacted with moisture soil dry unit weights obtained from gyratory compaction surpassed the dry unit weights of traditional compaction methods for the majority of soils tested; therefore, gyratory compaction was considered a feasible and effective method of laboratory soil compaction. A-4 was the only soil whose dry density did not surpass some of traditional compaction tests. Continued research is needed to develop a standardized protocol for gyratory compaction of soils as well as gain a more thorough understanding of free-draining soil. Future studies may also gain a better understanding of gyratory compaction by comparing dry unit weights, pressures, or energies of gyratory compaction to field compaction instead of existing laboratory compaction techniques.