Abstract
AbstractThe presence of gas hydrates (GHs) increases the stiffness and strength of marine sediments. In elasto‐plastic constitutive models, it is common to consider GH saturation (Sh) as key internal variable for defining the contribution of GHs to composite soil mechanical behavior. However, the stress‐strain behavior of GH‐bearing sediments (GHBS) also depends on the microscale distribution of GH and on GH‐sediment fabrics. A thorough analysis of GHBS is difficult, because there is no unique relation between Sh and GH morphology. To improve the understanding of stress‐strain behavior of GHBS in terms of established soil models, this study summarizes results from triaxial compression tests with different Sh, pore fluids, effective confining stresses, and strain histories. Our data indicate that the mechanical behavior of GHBS strongly depends on Sh and GH morphology, and also on the strain‐induced alteration of GH‐sediment fabrics. Hardening‐softening characteristics of GHBS are strain rate‐dependent, which suggests that GH‐sediment fabrics dynamically rearrange during plastic yielding events. We hypothesize that rearrangement of GH‐sediment fabrics, through viscous deformation or transient dissociation and reformation of GHs, results in kinematic hardening, suppressed softening, and secondary strength recovery, which could potentially mitigate or counteract large‐strain failure events. For constitutive modeling approaches, we suggest that strain rate‐dependent micromechanical effects from alterations of the GH‐sediment fabrics can be lumped into a nonconstant residual friction parameter. We propose simple empirical evolution functions for the mechanical properties and calibrate the model parameters against the experimental data.
Highlights
In marine and permafrost soils, gas hydrates (GH) can be present in large amounts and at high relative saturations (Wallmann et al, 2012)
The overall stress‐strain behavior of GH‐bearing sediments (GHBS) in this study suggests that GH structures and GH‐sediment fabrics dynamically rearrange in response to specific strain histories and loading events, and sediment shear strength is influenced by how fast plastic deformation occurs
This study shows that strain rate‐dependent effects influence the hardening‐softening characteristics and stress‐strain behavior of GHBS
Summary
In marine and permafrost soils, gas hydrates (GH) can be present in large amounts and at high relative saturations (Wallmann et al, 2012). Considerable effort is invested in geotechnical testing of GHBS to better understand geomechanical properties and stress‐strain behavior in slope failure events or GH production scenarios. In particular with the perspective on sand production issues during natural gas production and potential slope failure of fine‐grained sediments, the effects of fines content (Hyodo et al, 2017; Jung et al, 2012; Kajiyama, Hyodo, et al, 2017; Lee, Santamarina, et al, 2010; Yun et al, 2007), lithology and consolidation history (Fujii et al, 2015; Ito et al, 2015; Santamarina et al, 2015; Suzuki et al, 2015; Yoneda et al, 2015a), and thermo‐ hydro‐chemo‐mechanical process coupling (Gupta et al, 2017; Klar et al, 2013; Sánchez et al, 2017; Uchida et al, 2016) have received attention
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