Influence of test conditions and soil properties on the geomechanical response of hydrate-bearing sands

Testing of natural hydrate-bearing sands (HBSs) exhibits differences in their geomechanical behavior, both in terms of stiffness and shear strength, which may result from differences in hydrate saturation, confining stresses, along with minor differences in particle size distribution (PSD) between the sands. Results from laboratory studies on synthesized hydrate-bearing specimens have sought to consider the effect of PSD, hydrate saturation, and confining stresses on the geomechanical behavior of HBS, although these were limited in scope. Therefore, to gain better insights into this inter-relationship, and the influence it may have on the geomechanical behavior of HBS, this paper reports on a more detailed series of tests conducted on laboratory-synthesized HBS specimens. Tests were carried out using a specially designed triaxial apparatus including a resonant column drive head, which enabled detailed characterization of the evolving geomechanical properties of the sand specimen during the formation process. Observations suggest that the geomechanical response of the specimens is inherently related to the hydrate morphology that develops, and its distribution. These, in turn, are dependent on initial water saturation and suctions that are developed prior to hydrate formation, which are functions of soil properties and initial test conditions such as water saturation and applied stress state.