A bounding surface model of methane hydrate-bearing carbonate sand-silt mixtures

The geological environment of marine methane hydrate-bearing sediments (MHBS) is highly complex. Mastering the mechanical behavior of MHBS is crucial for analyzing geomechanical hazards and evaluating its stability. The marine sediment in the South China Sea (SCS) contains a significant amount of porous foraminifera shells, which serve as the primary storage space for natural gas hydrates and differ significantly from other sea areas. In the laboratory, porous carbonate sand (CS) and cohesion-less silt were utilized to prepare host sand of methane hydrate. In this paper, based on the analysis of experimental data, a bounding surface model was proposed to describe the mechanical behavior of artificial MHBS. The effect of methane hydrates on the elastic strain, normal consolidation and critical state of host sand is discussed, and corresponding equations for the model parameters are established, taking into consideration the cementing mechanism of hydrates. These equations are defined as functions of hydrate saturation, carbonate sand content (CSC), and initial void ratio. The increase in hydrate saturation significantly reduces the compressibility of the host sand and improves its strength. The proposed model is applied to predict the results of isotropic consolidation and drained triaxial tests on MHBS, demonstrating satisfactory performance.