含气海洋软土的水力特性试验研究及本构建模

The widely distributed soft soils in the nearshore and offshore areas of China pose enormous challenges to the development and utilization of underground and marine spatial space. The degradation of the organic matter present in these soils produces biogas which makes their hydro-mechanical behaviour extremely complex. Experimental difficulties to measure the gas pressure inside discrete gas bubbles have brought to accept the unrealistic assumption that the gas pressure and the water pressure are equal. By doing so, the capillary pressure effects are neglected thus causing uncertainty and misconceptions in interpreting the experimental data and in developing constitutive models for gas-bearing soft soils. In this project the typical soft clay from the Guangdong-Hongkong-Macao Greater Bay Area is used as reference soil. Artificially charged gassy samples will be prepared and tested in triaxial apparatuses. A new experimental methodology will be adopted to quantify directly the pore gas pressure and degree of saturation in gas-bearing soft soils. Overcoming this strong limitation represents a research breakthrough which allows to extend the framework of unsaturated soil mechanics to gas-bearing soft soils. Knowledge of the pore gas pressure can substantiate the adoption of an equivalent “soil-water characteristic curve” for gassy soils with the gas pressure as additional variable. This allows to establish a new constitutive model for unsaturated gas-bearing soft soils. The second part of the project focuses on validating a new constitutive elastic-plastic framework for gas-bearing soft soils based on the experimental results of the first part. The experimental and numerical results of this project will improve the geotechnical knowledge on gas-bearing soft soils mechanics, and provide a scientific basis for the construction and maintenance of engineering civil infrastructures founded on gas-bearing soft soils.

广泛分布于近岸和离岸的海洋软土给我国地下和海洋空间开发利用带来了巨大的挑战。软土中有机质降解产生的游离相生物气使软土的水-力特性更加复杂。由于游离气泡内的孔隙气压力无法直接测量，以往的研究中一般假定孔隙气压力等于孔隙水压力，忽略了作用在土颗粒上的表面张力，给试验结果的解释和模型建立带来了很大的不确定性。本项目以分布于粤港澳大湾区的典型软土为主要研究对象，人工制备含气软土试样并开展一列的室内试验，改进试验方法获取含气土中孔隙气压力和饱和度的信息，量化含气土中表面张力对强度的贡献；基于非饱和土力学理论，引入将孔隙气压力作为变量的“水土特征曲线”，建立新的非饱和含气软土弹塑性本构模型；开展数值模分析并验证理论模型。本项目成果将进一步完善含气软土力学的理论，同时为以软土为地基的工程设施的建设和维护提供科学依据。

广泛分布于近岸和离岸的海洋软土给我国地下和海洋空间开发利用带来了巨大的挑战。海洋软土致灾机理主要包括强度和变形两方面。软土中有机质降解产生的游离相生物气使软土的水-力特性更加复杂。本项目以分布于粤港澳大湾区的典型软土为主要研究对象，开展了系列的试验，揭示了干旱气候作用下土体水分蒸发-收缩-结构演化规律及其耦合作用关系；阐明了干旱气候作用下土体工程性质（压缩/渗透特性）响应; 阐明了土中植物纤维对土体工程性质灾变过程的影响。针对含气土改进试验方法获取含气土中孔隙气压力和饱和度的信息，量化含气土中表面张力对强度的贡献；基于非饱和土力学理论，引入将孔隙气压力作为变量的“水土特征曲线”，建立新的非饱和含气软土弹塑性本构模型。本项目成果进一步完善含气软土力学的理论，同时为以软土为地基的工程设施的建设和维护提供科学依据。本项目出版英文专著1项，完成SCI收录论文6篇，EI文章1篇，获得中国和美国发明专利各1项，获得实用新型专利3项。