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Methane hydrate as a “new energy” 251

7.3.4 Triaxial compression tests

7.3.4.1 Testing condition
The experimental conditions were considered to be equivalent to in situ conditions. In
the experiments, the specimens were subjected to different levels of effective confin-
ing pressure (1, 3, 5 MPa), back pressure (5, 10, 15 MPa), and temperature (1°C, 5°C,
10°C). For all tests, a shearing rate of 0.1% min 1 was adopted. Tests were performed
on two sets of specimens, porosity n¼40% (relative density D r ¼90%) and n¼45%
(D r ¼40%), with various MH saturation ratios. The maximum deviator stress indi-
cated in the table refers to the peak stress obtained from the deviator stress-axial strain
relation; however, if a peak was not observed, the deviator stress corresponding to
15% axial strain was used.

7.3.4.2 Test results
The initial shear modulus increased with MH saturation due to the increased level of
particle bonding (Fig. 7.12). This effect was still evident up to 15% axial strain. The
Toyoura host sand demonstrated contractive behavior under high confining pressures.

Fig. 7.12 Variation of deviator stress and volumetric strain with axial strain at different MH
saturation [18].