The engineering behavior of compacted clay has been extensively investigated by many researchers. It is widely accepted that the composition and structure of compacted clays are among the fundamental factors influencing the engineering properties of clays. Moreover, the structure is strongly influenced by the chemical composition of clay particles, the molding water content at compaction, and the amount and nature of externally applied compaction energy.
It appears that there exists no unique relationship based on soil type between changes in the structure of compacted clays and their engineering behavior. The only way to ascertain the influence of molding water content and method of compaction on the structure and engineering properties of any given clay is by direct determination in the laboratory.
The present test program was carried out to investigate the influence of different methods of compaction on the structure and the as-compacted undrained strength of Leda clay. Three methods of compaction were used, that is static, kneading, and impact. Samples of Leda clay were prepared by each method using three different compactive efforts. For purposes of comparison between the different methods of compaction, the applied pressures used, in case of kneading and static compaction, were chosen so as to give essentially the same maximum dry density for compacted samples, as obtained by impact compaction. This resulted in compaction curves having approximately the same relative positions with respect to the zero air-voids curves, as the impact curves. The as-compacted undrained strength of the compacted soil, at 1% and 2% strain, was taken as the measure to indicate any changes that might have taken place in the structure of compacted soil. The effect of increasing the compactive effort on strength of compacted soil was also investigated.
The results of the laboratory investigation conclusively show that for this specific soil the strength of the compacted Leda clay is controlled by the method of compaction Impact and kneading methods of compaction have sufficiently similar effect on the compacted soil that the strength associated with the two methods is essentially the same. Static compaction, however, results in higher strengths.
The test results also show that to the dry-side of the optimum moisture content, the as-compacted strength of Leda clay progressively increases with increasing the dry density. At water contents in the vicinity or wet of optimum, strength for samples prepared by kneading or impact compaction is markedly reduced with increasing the dry density. For samples prepared by static compaction, however, the strength progressively increases with increasing the dry density.
The experimental results are in line with the findings of other investigations. Previous investigations showed that the structure of compacted clay is controlled by the method of compaction. The data are in excellent accordance with the concept that shear during compaction is primarily responsible for changes in the structure and strength of compacted clay caused by the different methods of compaction.