Evaluation of failure modes and undrained shear strength by cone penetrometer for Natural Gas hydrate-bearing pressure-core sediment samples recovered from the Krishna–Godavari Basin, offshore India

Abstract

Compressional wave velocity measurements and cone penetration tests were carried out for pressure cores recovered from the Krishna–Godavari Basin off the eastern coast of India, using an instrumented pressure testing chamber constructed by the Japanese National Institute of Advanced Industrial Science and Technology. For pressure cores with high gas hydrate saturations (Sh) and exhibited high compressional wave velocities also display a high loading force that resulted in tensile failure. A pressure core sample with low compressional wave velocities and low gas hydrate saturations led to a low loading force, which resulted in radial shear. The cone factor connecting the cone resistance and the undrained shear strength, Nk, was estimated using cone penetration testing and the uniaxial compressional results. We estimated its value as Nk = 45 by using a uniaxial compression loading speed of 0.01%/min and a cone insertion loading speed of 0.25 mm/s. Undrained shear strengths, estimated from cone penetration results using Nk = 45, were assumed to be equal to the tensile strengths between hydrate-hydrate and hydrate-particle interface when Sh is less than 50% and increases when Sh is more than 50% assuming that gas hydrate morphology was matrix supporting.