Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japanese Geotechnical Society  

DOI： 10.1016/j.sandf.2022.10117

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：(MISC) Introduction and explanation (others)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPANESE GEOTECHNICAL SOC  

Depressurization is an effective method to produce methane gas from methane hydrate reservoirs. However, during gas production, sediments consolidate due to increasing effective stress. Revealing the compressive characteristics of methane hydrate-bearing sands during consolidation is essential for an accurate understanding of sediment properties and for the development of a constitutive model. Therefore, a series of isotropic consolidation tests was performed on sand in which methane hydrate was artificially generated, and its compressibility characteristics were evaluated. Furthermore, to assess prolonged production, creep compressive behavior was investigated. The experimental results showed volumetric strain due to increasing confining stress decreased with increasing initial methane hydrate saturation. Particle crushing during consolidation was inhibited by the presence of methane hydrate. It was confirmed that the increase in the effects of methane hydrate on soil compressibility followed a power function with the increase in methane hydrate saturation. Creep deformation was observed during the stress holding period regardless of the presence of methane hydrate. Creep behavior during the stress holding period was related to the extent to which the creep component had dissipated before the stress holding period in the past. A theoretical concept for creep strain was proposed based on the experimental results. (C) 2021 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.

DOI： 10.1016/j.sandf.2021.01.011

Web of Science

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

J-GLOBAL

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCI LTD  

A series of triaxial compression tests were performed on the methane hydrate-bearing sands formed with rounded glass beads and natural sands to,examine their mechanical properties. The effect of particle characteristics on the mechanical response of methane hydrate-bearing sands with regard to the exertion of bonding force and de-bond mechanism between grains is explained from the grain-scale viewpoint. In comparison with the natural sand, methane hydrate-bearing glass beads owns a similar initial stiffness and rapidly attains the peak shear strength at a smaller axial strain. The obvious post-peak strain-softening behaviour of methane hydrate-bearing glass beads which differs from the tender post-peak strain-softening tendency of methane hydrate-bearing natural sand is observed. It is attributed to almost simultaneous exfoliation of hydrate mass from the glass beads with smooth surface within the straightly sheared layers. The substantial resource of shear strength enhancement for methane hydrate-bearing glass beads is the cohesion but the shear strength of methane hydrate-bearing natural sand was jointly governed by the cohesion and angle of internal friction. In contrast to the increasing tendency of difference of shear strength with the level of effective confining pressure for methane hydrate-bearing natural sand, the methane hydrate-bearing glass beads exerts a stronger effect of bonding force on the difference of shear strength at relatively lower pressures but this effect decreases at higher pressures. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jngse.2017.05.008

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPANESE GEOTECHNICAL SOC  

It is recognized that methane hydrate (hereafter referred to as MH) is trapped in the sand sediments of alternating sand and mud layers in the turbidite of the Nankai Trough, Japan. The existence of fines within the marine sediment significantly affects its mechanical and physical properties. A series of plane strain compression tests at high pressures were performed in order to investigate the effect of the particle characteristics and fines content of the host sands on the shear behaviour of MH bearing sands. MH bearing sands were artificially produced using rounded glass beads and three other silica sands with different fines contents. A high-pressure low-temperature testing apparatus was equipped with a camera to observe deformation of the specimens during shearing and particle image velocimetry analysis was conducted on pictures taken during the experiments. The experimental results show that strength enhancement due to the bonding effect in MH bearing sand increases with the level of fines content. Values for both the cohesion and friction angle of MH bearing sand composed of Toyoura sand increased along with increasing MH saturation. However, in the case of MH bearing glass beads, only the value for cohesion increased when MH was formed. The maximum shear strain of MH bearing glass beads was mostly concentrated near the shear band. While the maximum shear strains of the three other MH bearing sands were concentrated within the shear band, some was widely distributed in the region outside of the shear band. A rise in the degree of MH saturation increased the angle and narrowed the width of the shear band, regardless of the fines content. (C) 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.

DOI： 10.1016/j.sandf.2017.03.002

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TECHNO-PRESS  

A series of high-pressure isotropic compression tests were performed on four types of poorly graded silica sand that were artificially prepared based on representative grading curves and similar mineralogy composition of seabed sediment containing different fines contents existing in the Nankai Trough. The addition of fines steepens the initial compression path and increases the decrement of the void ratio after loading. The transitional behaviour of the poorly graded sand with a larger amount of fines content was identified. The slope of the normal compression line shows a slight decreasing tendency with the level of fines content. The bulk modulus of silica sand with fines was lower when compared with the published results of silica sand without fines. A small amount of particle crushing of the four types of poorly graded sand with variable fines content levels was noticed, and the results indicated that the degree of particle crushing tended to decrease as the fines content increased.

DOI： 10.12989/gae.2017.12.1.127

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)  

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Asian Regional Conference on Soil Mechanics and Geotechnical Engineering  

Methane Hydrate (hereafter referred to as MH) is being researched and developed in order to prepare for production in the Nankai Trough of Japan. The grain size distribution and the degree of MH saturation of MH bearing sand varies based on location with varying fines content. Also, the shear behaviour is affected by particle shape. In order to investigate the effect of the characteristics of host sand on the shear behaviour of MH-bearing sands, MH was artificially produced in specimens composed of four kinds of materials with varying particle shape, fines content and degree of MH saturation. In this study, a high stress and low temperature triaxial plane strain testing apparatus was used. A marked increase in stiffness and strength was observed in all MH-bearing materials. In the case of glass beads, higher peak stress appeared in MH-bearing material than that without MH and the softening behaviour of MH bearing sand after peak strength was most predominant. In the case of MH-bearing sand, an increase in fines content leads to an increase in strength. An increase in degree of MH saturation leads to an increase of the angle of the shear band and the width of shear band becomes narrower.

DOI： 10.3208/jgssp.JPN-123

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MINERALOGICAL SOC AMER  

Understanding the mechanical behaviors of carbon dioxide/methane hydrate-bearing sediments is essential for assessing the feasibility of CO2 displacement recovery methods to produce methane from hydrate reservoirs. In this study, a series of drained triaxial compression tests were conducted on synthetic carbon dioxide hydrate-bearing sediments under various conditions. A comparative analysis was also made between carbon dioxide and methane hydrate-bearing sediments. The stress-strain curves, shear strength, and the effects of hydrate saturation, effective confining stress, and temperature on the mechanical behaviors were investigated. Our experimental results indicate that the newly formed carbon dioxide hydrate would keep the reservoir mechanically stable when CH4-CO2 gas exchange took place in a relatively short period of time and spatially well distributed in the pore space. Experiments of CO2 injection in methane hydrate-bearing sediments are necessary to confirm this hypothesis.

DOI： 10.2138/am.2014.4620

Web of Science

Event date： 2023.7

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：新潟県  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：新潟市  

Event date： 2022.7

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：新潟市  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)