三轴剪切条件下胶结型深海能源土应变局部化离散元模拟分析  

Strain localization formation of deep-sea methane hydrate-bearing soils by discrete element simulation of the triaxial test

作　　者：王思远[1] 蒋明镜 李承超[2] 张旭东 WANG Si-yuan;JIANG Ming-jing;LI Cheng-chao;ZHANG Xu-dong(Department of Civil Engineering,School of Civil Engineering,Tianjin University,Tianjin 300350,China;School of Civil Engineering,Suzhou University of Science and Technology,Suzhou,Jiangsu 215009,China;State Key Laboratory for Disaster Reduction in Civil Engineering,Tongji University,Shanghai 200092,China;Department of Geotechnical Engineering,College of Civil Engineering,Tongji University,Shanghai 200092,China)

机构地区：[1]天津大学土木工程学院土木工程系,天津300072 [2]苏州科技大学土木工程学院,江苏苏州215009 [3]同济大学土木工程减灾国家重点实验室,上海200092 [4]同济大学土木工程学院岩土工程系,上海200092

出　　处：《岩土力学》2023年第11期3307-3317,3338,共12页Rock and Soil Mechanics

基　　金：国家重大自然灾害防控与公共安全重点专项(No.2022YFC3003403);国家自然科学基金创新研究群体项目(No.42221002);国家自然科学基金重大项目(No.51890911);江苏省高等学校基础科学(自然科学)研究面上项目(No.22KJB570004);海南省重点研发计划项目(No.ZDYF2021SHFZ264)。

摘　　要：天然气水合物(后简称为“水合物”)开采期间会导致其储层的变形和破坏,继而引发一系列的工程问题。为实现水合物安全有效的开采,需要对其赋存条件下的水合物沉积物(后称为“能源土”)的剪切变形特性进行相应研究。采用温-压-力-化胶结接触模型用以考虑水合物的胶结效应和对赋存环境温度压力的敏感性。此外,柔性边界被应用于离散元模拟的三轴剪切试验,用以保证剪切带的充分演化。通过考虑局部变形、孔隙率、平均纯转动率、胶结破坏及组构各项异性等变量研究了剪切带的形成规律及其宏微观机制。结果表明:(1)在三轴剪切试验中所采用的柔性边界在有效模拟深海能源土的应力-应变及体变响应的同时保证了试样的自由变形。(2)剪切带在剪切初期应变硬化阶段已经开始萌发,并在应变软化阶段愈发明显。(3)剪切带内外宏微观参量例如颗粒转动、局部孔隙率变化等均表现出明显差异。(4)水合物胶结的存在对于其宿主砂土具有双重作用,一方面增强了其强度特性,另一方面作为剪切过程中的薄弱环节率先发生破坏促使剪切带的萌发。研究结果对于理解深海能源土变形中的细观演化机制具有参考价值。Exploiting methane hydrate induces deformation and damage to the reservoir,leading to a series of geotechnical engineering problems.Therefore,to achieve safe and effective extraction of hydrates,it is necessary to research the shear deformation characteristics of methane hydrate-bearing sediments(MHBS).The thermo-hydro-mechanical-chemical(THMC)microscopic contact model was utilized to account for hydrate cementation effects and their sensitivity to environmental temperature and pressure.In addition,the flexible boundary was applied to triaxial numerical tests to ensure the full evolution of shear bands.The microscopic mechanism of onset and development of shear bands was studied by considering macro and micro variables such as strain localization,porosity,average pure rotation rate(APR),bond failure,and spatial distribution of shear band.The results indicate that the flexible boundary used in the triaxial shear test effectively represents the stress-strain and volumetric response of MHBS while ensuring the free deformation of the sample.The shear band has already begun to germinate and to develop during the initial strain hardening stage and becomes more pronounced once it reaches the strain softening stage.Considerable disparities exist in macro-and microscopic parameters,including particle rotation and porosity alterations,both within and outside the shear band.Furthermore,hydrate cementation exerts a dual impact on its host sand.On the one hand,it enhances its strength characteristics,and on the other hand,as a weak link in the shear process,it takes the lead in failure,thus contributing to the emergence of shear bands.The research results have reference value for understanding the mesoscale evolution mechanism of MHBS deformation.

关 键 词：能源土 离散元法 应变局部化 宏细观机制 

分 类 号：TU441[建筑科学—岩土工程]