Characterization of deep sea sediments from the continental margin off Costa Rica

A series of laboratory studies is conducted to explore the characteristics, mechanical properties, and geophysical parameters of sediments using both undisturbed and remolded specimens from the continental margin off Costa Rica. The tested specimens, consisting of uncemented quartzitic fine sand with a high fraction of fines, are obtained at the depths of 20.69 mbsf (meter below seafloor) to 510.49 mbsf. Laboratory-derived index properties of natural sediments could be employed to provide further more engineering design parameters based on accumulated geotechnical knowledge. The major mineral constituents are several non-clay minerals with various clay minerals including kaolinite, chlorite, and montmorillionite. The observed microstructures are compatible with a typical marine sedimentation environment. Specimens are systematically studied using an oedometeric cell instrumented to study the evolution of small strain stiffness, electromagnetic properties, and volume change. The results indicate that effective stress and porosity are the major controls of the mechanical and geophysical properties. Thermal conductivity measurements reveal that the effective thermal conductivity is governed by not only the bulk conductivity and volumetric fraction of each component but also by the quality of the interparticle contacts and number of contacts per unit volume.