Influence of degree of saturation and degree of compaction on unsoaked CBR values

Abstract

For the satisfactory performance of soil structures, it is conventional to control soil compaction by focusing on the dry density (𝜌𝑑 ) and water content (𝑤) relative to the maximum dry density (𝜌𝑑 ) max and optimum water content (𝑤𝑜𝑝𝑡 ) determined by standard laboratory compaction tests at a specific compaction energy level (CEL)[1]. However, both (𝜌𝑑 )max and 𝑤𝑜𝑝𝑡 are significantly affected by variations in soil type and CEL, which are often difficult to accurately estimate or control in the field. Importantly, the resultant stress-strain, stiffness, and hydraulic properties of compacted soil, such as the California Bearing Ratio (CBR), are controlled not merely by 𝜌𝑑 and 𝑤 , but fundamentally by the 𝜌𝑑 and the degree of saturation (𝑆𝑟 ) achieved during compaction[1]. This is because the physical properties are governed by the effective stress state and the micro-structure, both of which are strongly influenced by the matric suction during compaction, a function of 𝑆𝑟 [1] . This study investigates the fundamental variation of CBR values concerning the degree of compaction and under conditions of constant moisture content, thereby clarifying the mechanisms that govern soil strength under coupled density-saturation changes.