THE EFFECT OF LABORATORY COMPACTION ON THE COMPRESSIBILITY OF A COMPACTED HIGHLY PLASTIC CLAY

The compressibility of the plastic St. Croix clay is to be studied for both laboratory and field compaction. This interim report deals with the laboratory-compacted phase. The clay was compacted to three levels of kneading type effort and at water contents dry of optimum, at optimum and wet of optimum. As compacted compressibilities were assessed in the oedometer, and compaction prestress values were interpreted from the e-log p curves. These values were always less than the compaction pressures previously applied to the soil. A statistically valid prediction equation for prestress was written in terms of the compaction pressure and an interaction between compaction pressure and compaction water content. Other compacted samples were saturated under confinement, with the aid of vacuum and backpressure. The volume changes incurred depended upon the compaction variables as well as the confinement. It was possible to develop a correlation between this volumetric strain and the compaction pressure and water content. Soaked compressibilities were also measured and compared with the as-compacted values. Comparable studies with samples of field compacted clay are under way, and will be reported in a separate report. (FHWA)