The microfabric of deep-sea illitic clays was investigated using electron microscopy in support of the In-Situ Heat Transfer Experiment (ISHTE) Simulation test (ISIMU) and the Subseabed Disposal Program (SDP), Sandia National Laboratories. ISHTE and the field exercises were designed to investigate the thermal, fluid, and mechanical response of the sediment to the emplacement of radioactive waste in the seabed. Clay fabric of an undisturbed core sample, designated RAMA, was compared to dredged, remolded, reconsolidated material in order to investigate the (1) effects of mechanical disturbances from sediment remolding and heater probe insertion and (2) effects of induced thermal gradients caused by heating of the sediment.

Aggregates of finely divided particulate material, having intra-voids, maintain structural integrity in spite of remolding in the laboratory. The surficial illitic clay can be reconstituted in the laboratory and be used for geotechnical simulation tests. Dredged sediment was remolded and reconsolidated to equivalent in-situ porosities by the Department of Ocean Engineering, URI, and used in the ISHTE simulation test. No differences in the microfabric significantly affecting the bulk physical properties were observed between remolded and undisturbed sediment. Samples in proximity to the heater probe revealed some slight preferential clay particle alignment probably caused by shearing stresses, which developed in the sediment during probe insertion. Heating of the sediment temperatures slightly below 300°C did not appear to have a significant effect on the fabric, with the exception of localized “quasi-expansion” and flow features observed in the microfabric in the near field.

Aggregates of finely divided particulate material, having intra-voids, maintain structural integrity in spite of remolding in the laboratory. The surficial illitic clay can be reconstituted in the laboratory and be used with confidence for simulation tests.