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Methane hydrate‐bearing sediments with different amounts of fines content and at three densities were artificially prepared under controlled temperature and pressure conditions. The void ratios of specimens after isotropic consolidation tend to decrease with a rise in fines content. The fines particles enter into the pore space between sand grains and densify the specimens. A series of triaxial compression tests were performed to systematically investigate the influences of fines content and density on the shear properties of hydrate‐free sediments and methane hydrate‐bearing sediments. The test results demonstrate that a rise in fines content within methane hydrate‐bearing sediments significantly enhances peak shear strength and promotes dilation behavior. These influences are particularly prominent for specimens at loose packing state. A decrease in void ratio increases the shear strength and stiffness of hydrate‐free sediments and methane hydrate‐bearing sediments containing fines content of 0% and 8.9%. It is noted that the formation of methane hydrate in samples with varying amounts of fines content increases the stress ratios at the critical state. The addition of fines particles into coarse‐grained sand grains alters the internal microstructure of sand matrix and the hydrate formation pattern in the pore space between sand grains and fines particles.

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A series of high-pressure compression tests with various stress paths under monotonic and cyclic loadings were performed to examine the compression and particle crushing characteristics of silica sand in a dense state. Different stress paths were particularly designated to individually investigate the influences of mean and shear stress on particle crushing. Test results show that the degree of particle crushing increases with the stress level and is pronouncedly affected by the stress paths. For each compression test following a designated stress path, an increase in the cyclic loading number also enhances the degree of particle crushing.Particle morphology is affected by the accompanying occurrence and evolution of grain damage. Notably, the relative breakage expresses a liner relationship with the maximum volumetric strain during monotonic and repeated compression loadings. A good correlation between the relative breakage and plastic work per unit volume is obtained for silica sand at various mean stresses regardless of the stress history. However, this correlation is affected by cyclic loading number because of different crushing mechanisms. During the entire cyclic compression process, the increasing rate of relative breakage is lower than the plastic work increment for dense silica sand as the cyclic loading progresses.

A series of undrained monotonic and cyclic triaxial tests were performed on silica sand at two initial densities and different confining pressures from 0.1 to 5 MPa to investigate their shear response and crushing behaviour. The influence of particle crushing on the undrained shear strength and pore-water pressure was examined. To clarify the evolution of particle crushing, undrained monotonic and cyclic tests were terminated at several distinctive stages and sieving analysis tests were subsequently performed on the tested specimens. In the undrained monotonic test, specimens exhibited remarkable dilation behaviour and experienced no apparent particle crushing at low confining pressures. An increase in the mean stress suppressed the dilatancy due to a faster increase of the pore-water pressure, giving rise to the occurrence of particle crushing. In the undrained cyclic test, a higher confining pressure and cyclic stress ratio resulted in a much higher relative breakage. At a specific cyclic stress ratio, the relative breakage increased as the cyclic loading progressed. The confining pressure and shear strain amplitude played a significant role in controlling the evolution of particle breakage. The correlation between the relative breakage and plastic work for specimens under isotropic consolidation, undrained monotonic, and cyclic loadings has been validated experimentally.

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