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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Japan has large areas covered by volcanic ash sediments. Volcanic coarse soils of their sediments are used in earth structure well. However, most of such soils are classified in problematic soil. Their constituent particles are very porous. Therefore, it is anticipated that measurements of soil tests using volcanic soil are spread, especially physical property tests, when soil tests are conducted under JIS/JGS methods. In this study, a series of density tests of soil particle and grain size analyses was performed on a few volcanic coarse soils with intra-particle void to consider the influence factors on spread of experimental results. As a result, the physical properties of volcanic coarse soils were affected remarkably by the sample preparation and experimental method rather than the uncertainly of test process or measurement. Hence, it is necessary for the quality evaluation in such materials to consider the homogeneity and preparations situation of the sample enough.