Strength of field compacted clays

Abstract

The reported research established the relationships among the compaction variables (dry density, water content, roller type, and number of passes) and the shearing behavior of a residual clay (St. Croix) from sandstone and shale. Compacted material was tube sampled from test pads, and subjected to two test series: unconsolidated-undrained (UU), and saturated consolidated-undrained [Formula: see text] triaxials. Both test series were run at various confining pressures to approximate the end of construction and long-term conditions for several embankment depths.The UU tests showed an increase in strength with an increase in density or a decrease in water content. For the as-compacted samples, significant volume changes occurred during shear. The volumetric strain at failure decreased with increasing prestress effected by the roller.In the [Formula: see text]testing program, sample behavior after saturation under confinement was interpreted in terms of initial compacted conditions (and confinement). The effective stress strength parameters were functions of the compacted water content and void ratio. For a given initial void ratio, as the compaction water content increased, c′ increased and [Formula: see text] decreased. The volumetric strain upon saturation varied with the compacted water content, dry density, compactive energy, and the level of confinement. Skempton's A factor at undrained shear failure was dependent upon the initial void ratio and the degree to which the sample had been prestressed by the roller.Statistically valid regression equations for these dependent variables, viz., as-compacted strength, percent volume change due to saturation and consolidation, Skempton's A parameter at failure, and the effective stress strength parameters, were developed for field compacted St. Croix clay. Uses for such equations are given.