Importance of Controlling the Degree of Saturation in Soil Compaction

摘要

In the typical conventional fill compaction, the dry density ρ_d and the water content w are controlled in relation to (ρ_d)_(max) and w_(opt) determined by laboratory compaction tests using a representative sample at a certain compaction energy level CEL. Although CEL and actual soil type affect significantly the values of (ρ_d)_(max) and w_(opt), they change inevitably in a given earthwork project while CEL in the field may not match the value used in the laboratory compaction tests. Compaction control based on the stiffness of compacted soil in the field has such a drawback that the stiffness drops upon wetting more largely as the degree of saturation, S_r, of compacted soil becomes lower than the optimum degree of saturation (S_r)_(opt) defined as S_r when (ρ_d)_(max) is obtained for a given CEL. In comparison, the value of (S_r)_(opt) and the ρ_d/(ρ_d)_(max) vs. S_r-(S_r)_(opt) relation of compacted soil are rather insensitive to variations in CEL and soil type, while the strength and stiffness of unsoaked and soaked compacted soil is controlled by ρ_d and "S_r at the end of compaction". It is proposed to control not only w and ρ_d but also S_r so that S_r becomes (S_r)_(opt) and ρ_d becomes large enough to ensue soil properties required in design.