气体积聚或释放引起的含天然气土的应力状态演化研究

The evolutions of the stress state of gassy soils due to the accumulation or release of the gas (i.e. the processes of the increase or decrease of gas pressure) considering temperature effects are studied by laboratory tests. For this purpose, a temperature-controlled triaxial test system for unsaturated soils is developed. The mechanism and affecting factors are analyzed under various mechanical loading and various temperatures; furthermore the hydraulic hysteresis characteristics and the consolidation mechanism are discussed under isothermal conditions during the accumulation or release of gas pressure in different temperatures. The effects on the soil-water characteristic curves during heating-cooling processes are also discussed, and furthermore the energy conversions between the three phase materials of the unsaturated soil due to heating-cooling processes are analyzed. Based on the theory of the thermodynamics, a mathematical model for describing soil-water characteristic curves of gassy soil is established by introducing a temperature factor. Based on the porous media theory, a specific expression of deformation work is proposed, and the expressions of the stress state of unsaturated soils (including effective stress, matric suction, gas pressure, etc.) conjugated with the strain of the various phase is further derived which also includes the influences of temperature. In the derived work and energy balance equations, the dissipation and transformation of the energy of the three phase materials in unsaturated soils is taken into account. These studies are the essential basis for the construction of constitutive models for unsaturated soils, which can be widely used in various engineering fields such as the extraction and storage of natural gas, the contaminant remediation, the transportation infrastructure in ocean, radioactive waste disposal, and the safety assessment of underground engineering construction, etc.

研制一个可控制温度的非饱和土固结压力室并与GDS三轴试验系统套装，研究气体积聚或释放过程中（即气体压力逐渐增大或减小过程），含天然气土的应力状态变量演化过程的物理机制及其影响效应，分析不同外力荷载和不同温度荷载等温条件下的持水滞回过程和固结机理，探索加热-冷却反复作用历史对含天然气土的持水特征曲线的影响。根据热动力学基本理论，引入温度效应影响因子，发展一个描述含天然气土的土-水特征曲线的数学模型。基于变形功的概念，建立一个包含温度效应影响的土骨架应力（即有效应力）、广义基质吸力和气相压力等状态变量演化的数学表达式，揭示外部荷载作用下含天然气土的三相物质的能量耗散和转换过程。这些研究可为进一步建立非饱和土的本构模型奠定基础，在诸如天然气开发和贮存、污染物治理、跨海交通基础设施建设、核废料处置、地下空间利用的安全评价等方面有重要的学术意义和应用价值。

研制了一个可控制温度的非饱和土固结压力室并与GDS三轴试验系统套装，研究气体积聚或释放过程中（即气体压力逐渐增大或减小过程），含天然气土的应力状态变量演化过程的物理机制及其影响效应，分析不同外力荷载和不同温度荷载等温条件下的持水滞回过程和固结机理，探索加热-冷却反复作用历史对含天然气土的持水特征曲线的影响。根据热动力学基本理论，引入温度效应影响因子，发展一个描述含天然气土的土-水特征曲线的数学模型。基于变形功的概念，建立一个包含温度效应影响的土骨架应力（即有效应力）、广义基质吸力和气相压力等状态变量演化的数学表达式，揭示外部荷载作用下含天然气土的三相物质的能量耗散和转换过程。. 基于颗粒固体流体动力学理论和混合物理论，结合改进的土水特征曲线（SWCC）模型，考虑温度和饱和度变化引发相应的颗粒层次能量耗散，提出了一个非饱和土的热水力耦合模型。模型引入颗粒熵和颗粒温度的概念，将土体颗粒层次的耗散机制及其引发的宏观能量耗散描述为迁移系数和能量函数模型，并通过热力学恒等式得出非弹性变形的本构关系。通过模型预测与试验结果的对比，证实了模型的有效性：不同吸力和温度下的固结压缩曲线不同，压缩曲线斜率受温度的影响较小，而受吸力的影响较大；恒定吸力和压力下加热会引起热膨胀或热收缩。对正常固结的饱和粉质黏土试样进行6次升温-降温过程的室内热固结试验。研究表明，无论是正常固结土样还是超固结土样，在经过多次温度循环荷载作用后，会呈现为明显的超固结效应。而在相同的循环次数下，温度荷载作用引起的超固结效应随围压的减小而更为明显。. 这些研究可为进一步建立非饱和土的本构模型奠定基础，在诸如天然气开发和贮存、污染物治理、跨海交通基础设施建设、核废料处置、地下空间利用的安全评价等方面有重要的学术意义和应用价值。

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