A series of phase equilibrium tests were performed to
explore the
influence of various experimental conditions, including initial water
content, dry density, and salt content, on the phase equilibrium behavior
of methane hydrate in fine- and coarse-grained sediments. The results
indicate that the phase equilibrium condition of pore hydrate is significantly
influenced by the adopted experimental conditions and the sediment
types. It is shown that in equilibrium, a unique relationship (the
soil hydration characteristic curve (SHCC)) exists among the temperature
shift, the unhydrated water, and the amount of dissolved salt. Under
salt-free conditions, the SHCC is independent of dry density for coarse-grained
specimens, whereas it is slightly influenced by the dry density for
fine-grained specimens. A recently developed phase equilibrium model
of pore hydrate, which can account for osmotic, capillary, and adsorptive
effects, is introduced to interpret the experimental results. It is
shown that the SHCC of the coarse-grained specimens can be very well
described by the model; for fine-grained specimens, however, the effect
of salt content on matric suction has to be taken into account in
the model prediction.