No abstract

No abstract

No abstract

Gas hydrate-bearing sediments recovered by pressure coring from the Krishna-Godavari Basin offshore India during the 2006 National Gas Hydrate Program (NGHP) expedition were characterized using the instrumented pressure testing chamber (IPTC). The IPTC studies provided longitudinal profiles of P-and S-wave velocities, electrical conductivity, and undrained penetration resistance. The formation consisted of fine-grained clayey sediments of high specific surface and high plasticity. X-ray images showed horizontal layering, pronounced heterogeneity from milli-to centimeter scales, with the presence of high-density nodules and both horizontal and sub-vertical gas hydrate lenses. Relative to reference values for sediments without hydrates, regions of high P-and S-wave velocities, low electrical conductivity, and high undrained shear strength were identified and correlated with regions of apparent high hydrate volume fractions in all tested specimens. Physical properties were monitored during the depressurization of pressure cores. The hydrate volume fraction was estimated to be 18.2%. The evolution of P-wave amplitude, electrical conductivity, and temperature showed gas generation and freshening upon phase transformation. The effect of sampling by pressure coring and the ensuing zero-effective stress condition were discussed.

The near-surface is covered with soil in most onshore and offshore locations. Soil characterization by sampling and in-situ testing techniques (e.g., cone penetration and pressure meters) faces unavoidable perturbation effects. On the other hand, low-power geophysical techniques cause no appreciable perturbation and provide an effective alternative for site assessment. In particular, near-surface site characterization using elastic and electromagnetic perturbations yields important information related to the soil mass, including the spatial distribution of materials, smallstrain elastic properties and electromagnetic characteristics. In turn, geophysical measurements can be associated with soil parameters relevant to geotechnical engineering analysis and design. This chapter presents information about elastic (smallstrain) and electromagnetic properties of soils and their relations to soil parameters. The goal is to explain physical links between geophysical measurements and soil properties, emphasize global trends, and highlight variables that exert first-order effects. The chapter includes simple, yet robust, concepts and relations that can be readily used in designing measurement procedures and in data interpretation. The information in this chapter is structured resembling Chapter 3 of this volume by Knight and Endres. Comprehensive coverage of equations, trends, and behavior discussed herein can be found in Santamarina et al. (2001).