CHARACTERISTICS OF IRREGULARLY SHAPED COMPACTION CURVES OF SOILS

Although the curve of dry density versus moisture content commonly yielded by the standard AASHO compaction tests contains a single maximum, some soils have produced more complicated curves. Because these soils have not been well studied, extensive work has been carried out to establish the existence of irregularly shaped curves. The primary effort was focused on examining, from both a macroscopic and a microscopic level, the characteristics that lead to such curves. The investigation has established 4 types of compaction curves: one with a single peak, one with an irregular 1 1/2 peak, one with a double peak, and one that is almost a straight line with no distinct maximum dry density or optimum water content noted. There is a correspondence between the index properties on the modified Casagrande's chart and the kind of curve. The mineral constituents of the soil samples also affect the shape of the moisture-density compaction curve.