Strain-Softening Characteristics of Hydrate-Bearing Sediments and Modified Duncan–Chang Model

Mengqiu Yan,Rongtao Yan,Haihao Yu,Yonghong Wang

doi:10.1155/2021/2809370

Mengqiu Yan, Rongtao Yan + Show 2 more

Open Access

https://doi.org/10.1155/2021/2809370

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Abstract

Marine hydrate exploitation may trigger the seabed geological disaster, such as seafloor collapse and landslide. It is critically important to understand the mechanical properties of hydrate-bearing sediment. Strain-softening observation is a typical behavior of hydrate-bearing sediment (HBS) and exhibits more significant at higher hydrate saturation. This paper performed a series of triaxial compression tests on methane hydrate-bearing sand to analyze the influence rule and mechanism of hydrate saturation on the strain-softening characteristic, stiffness, and strength and introduced the strain-softening index to quantificationally characterize the strain-softening behaviors of HBS with different hydrate saturations. Based on the analyses on the mechanical behavior of HBS, the Duncan–Chang model is extended to address the stress-strain curves of HBS. Two empirical formulas with hydrate saturation embedded are used to characterize the enhanced initial modulus and strength for HBS, respectively. To address the strain-softening behavior of HBS, the modified Duncan–Chang model introduced a damage factor into the strength of HBS. To validate the modified Duncan–Chang model, four different triaxial compression tests are simulated. The good consistence between simulated result and experimental data demonstrates that the modified Duncan–Chang model is capable of reflecting the influence of hydrate saturation not only on the stiffness and strength but also on the strain-softening characteristics of HBS.

Highlights

Methane hydrate is an ice-like clathrate compound formed by methane and water at the relative high pressure and low temperature
Yoneda et al [14] tested the mechanical behaviors of undisturbed specimen of hydrate-bearing sediment and compared to the artificial hydrate-bearing sediment specimen. e result demonstrated that both have similar stiffness and strength characteristics
Yoneda et al [16] carried out isotropic compression tests on hydratebearing pressure-core sediments recovered from the Krishna-Godavari Basin, offshore India. e result showed that the presence of hydrate reduces the compression index and swelling index. rough the triaxial shear test of methane hydrate-bearing sediments with different fine particle contents, Hyodo et al [17] suggested that the shear strength and dilatancy of HBS increase significantly with the increase of fine particle content

Summary

Introduction

Methane hydrate is an ice-like clathrate compound formed by methane and water at the relative high pressure and low temperature. According to the triaxial compression results, Miyazaki et al [24, 25] related the strength and stiffness to the hydrate saturation and confining pressure and modified the formulas of strength and stiffness for extending the original Duncan–Chang model to address the mechanical behaviors of HBS. To reflect the influences of dissociation time and dissociation temperature on the mechanical properties of HBS, Song et al [27] modified the Duncan–Chang model All these modified Duncan– Chang nonlinear elastic models have the ability of capturing the enhanced strength and stiffness of HBS, but the strainsoftening characteristic of HBS cannot be addressed. The modified Duncan–Chang model is capable of simulating the enhanced stiffness, strength, and strain-softening characteristic of HBS, which could have an important academic and engineering significance for methane hydrate exploitation

Experimental Illustrations

Results and Analyses

Constitutive Model Development

Ethical Approval