Summary

This study investigates rock properties of siliciclastic sediments at the time of deposition and the development/evolution of rock properties during their progressive burial. A total of 12 synthetic samples of sand-clay aggregates including 6 pure quartz sands and 6 sand-clay mixtures with different grain size, sorting and clay content were tested under uniaxial compression in dry condition while measuring the total porosity, bulk density and ultrasonic velocity during the test. The results show an almost systematic trend for initial porosity which increases with decreasing size of the sand grains and also increasing clay content in the sand-clay mixtures. The higher P- and S-wave velocities (Vp and Vs) are found in the studied samples as a function of increasing grain size and clay content. The sand-clay mixtures show more compaction and loss of porosity at high stress in comparison with well-sorted sand although they have higher initial porosity at zero stress level. Also, poor sorting in pure sand aggregates decreases the initial porosity significantly; however, the rate of porosity reduction is less than for corresponding well-sorted samples. Furthermore, the experimental data of a poorly-sorted sand sample and two representative samples of sand-clay aggregates were compared with well-sorted sands to investigate applicability of the friable sand model. The results of this comparative study contribute to evaluate and constrain the model parameters with respect to elastic and acoustic properties of unconsolidated sands.

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