The conventional fill compaction procedure usually controls the dry density ρd and the water content w referring to the maximum dry density (ρd)max and the optimum water content wopt determined by laboratory compaction tests performed at a certain compaction energy level (CEL). However, (ρd)max increases and wopt decreases with CEL, while, since Proctor (1933), CEL practically available in the field has been increasing and the required ρd value has generally been becoming higher for more satisfactory performance of soil structures. Besides, the values of (ρd)max and wopt change with soil type. In a single earthwork project, the actual CEL and soil type may vary and it is very difficult to accurately estimate the field CEL and identify the actual soil type at a given moment at a given place. Therefore, the actual values of (ρd)max and wopt are usually unknown. On the other hand, the optimum degree of saturation (Sr)opt defined as Sr when (ρd)max is obtained for a given CEL and the ρd/(ρd)max vs. Sr−(Sr)opt relation are rather independent of CEL and soil type. The unsoaked and soaked strength and stiffness and the saturated hydraulic conductivity are a function of ρd and compacted Sr not including CEL as a variable. It is proposed to control Sr of compacted soil to be close to (Sr)opt and ρd to be large enough to achieve the physical properties required in design, together with pre-compaction control of water content.
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