Influence of compaction condition on the UCS and structure of compacted loess

The engineering importance of compacted loess is now much greater than that of intact loess because of the occurrence of a large number of loess fill slopes and foundations in the last few years. Molding water content (MWC) and degree of compaction (DOC) (or dry density) are two key factors that determine the structure of compacted soil. However, it is not clear how MWC affects the mechanical behavior of compacted loess. In this study, compacted loess specimens were prepared under various compaction conditions to have different MWCs (i.e., 14, 16, 18 and 22%) or DOCs (i.e., 85, 90 and 94%). Unconfined compression tests were performed on these specimens and their counterparts, the effects of MWC and DOC on the mechanical behavior of compacted loess under unconfined condition were interpreted with the assistance of the measured pore-size distribution curves (PSDs), soil–water retention curves (SWRCs) and computed structural parameters. The results show that both MWC and DOC significantly affect the strength-deformation characteristics of compacted loess. When DOC and initial water content are given, the larger the MWC, the larger the unconfined compressive strength (UCS), and the greater the ductility of specimen because of the more uniform distribution of pores and higher suction. At a given MWC, the greater the DOC, the larger the UCS, and the greater the initial stiffness of specimen because of the closer particle arrangement. The initial structural parameter reduces with DOC and increases with MWC, indicating that the soil strength is more susceptible to disturbance from loading or soaking when DOC is smaller or MWC is larger. Consequently, this leads to a higher structure potential for compacted loess. The relationship between the initial structural parameter and UCS is not unique, indicating that the structural difference caused by different particle arrangements may still exist upon soaking, while the UCS of compacted loess grows with the initial structural parameter.