Mechanical properties and constitutive model of high-abundance methane hydrates containing clayey-silt sediments

This study was the first to examine the mechanical behavior of sediment-bearing methane hydrates (SBMHs) with hydrate abundance up to 80%. The experiment results showed that the stress-strain curves of the SBMH specimens were characterized by the elastic-plastic deformation or plastic-elastic-plastic deformation of the specimens, prominent strain softening, and a rounded head-like trailing peak shape with no obvious stress cusps. Increasing the hydrate content and pore pressure, and reducing the temperature significantly enhanced the peak strength and initial tangent modulus of the specimens, but led to a decline in the peak strain. New correlation equations for initial tangent modulus, peak strength, and peak strain depending on hydrate abundance, pore pressure, and temperature were developed. A modified hyperbolic constitutive model was proposed by introducing a correction term to the Duncan-Chang model that reflects the degree of specimen softening and considering the effects of the hydrate abundance, temperature, and pore pressure. The modified model satisfactorily revealed the strain-softening characteristics of the SBMHs and accurately reproduced the peak strength and strain of all experimental specimens, effectively characterizing the contributions of the hydrate content, pore pressure, and temperature to the stress-strain behaviors of the specimens.