Physical and geotechnical properties of drill core sediments in the Heuksan Mud Belt off SW Korea

Three drill core samples collected from the Heuksan Mud Belt off SW Korea have been used to characterize sediment properties in relation to seismic units and to interpret geotechnical properties as a function of burial depth. The physical property data were readily classified into seismic units: Unit I, Subunit II-a, Subunit II-b, Subunit III-a, Subunit III-b, and Pre-LGM (last glacial maximum), in descending order. Thus, the variations in physical properties reflect the relative characteristics of the seismic units. Moreover, the relationships between physical properties are well grouped by each seismic unit. These results suggest that the physical properties of these sediments are mainly controlled by depositional processes related to sea-level change as one of dominant sedimentary processes in the study area. Interestingly, the shear strength and velocity of Subunit II-b are characterized by cyclic variation. These characteristic patterns are likely related to periodic variation in sedimentary environments (e.g., wave- or tide-dominated environments) in the study area. Clay fabric investigations with depth using scanning electron microscopy are characterized by different clay particle arrangements (e.g., from edge-to-edge to face-to-face contact with depth) owing to compaction effect caused by overburden pressure with depth. The geotechnical properties of the Heuksan Mud Belt suggest that the shallow regions are apparently over consolidated probably due to the flocculated fabrics at shallow depths and that the regions have moderate compressibilities in spite of the high mud content in the sediments.