Numerical simulation of the microstructure and compression behavior of Eckernfِrde Bay sediments

Transmission electron microscope (TEM) studies conducted on sediments recovered using diver-collected cores and gravity cores from Eckernfِrde Bay in the Baltic Sea, Germany, reveal that the sediments consist of silt- to clay-sized sediment, both free and bound into fecal pellets, organic matter, biogenic materials, methane gas and microorganisms. The microstructure of the upper 2 m of the sediment is complex, with the clay particles arranged in a very open structure with variable inter- and intra-domain pore space. In an effort to understand the relationship between microscopic variables (e.g., microfabric) and macroscopic geotechnical properties (e.g., compressibility), a numerical study was performed using the discrete element method. The objective of this study was to develop an understanding of the micro- to macro-linkage of mechanical properties. Specifically, one-dimensional compression behavior of the sediment was numerically simulated and compared with experimental data. Compositional parameters of the sediment were obtained from specific tests conducted at the Naval Research Laboratory and from tests conducted by other researchers participating in the project. Image analysis was used to quantify the microfabric parameters from TEM images of the sediment. The effect of organic matter was simulated by introducing inter-particle contact cementation. Results indicate that inter-particle bonding due to inter-particle cementation and/or the van der Waals attractive force (1) contributes to the apparent overconsolidation observed in the laboratory and (2) holds the highly porous, unstable microstructure together until a threshold stress level is reached. Change in void ratio during compression is due to inter-, rather than intra-domain movement.