【作者】 徐浩峰；

【导师】 朱向荣； 谢康和；

【作者基本信息】 浙江大学 ， 岩土工程， 2011， 博士

【摘要】 以往常将水面以下的土体视为饱和土,而实际上由于多种原因,土体中往往含有气泡。由有机质分解所形成的生物气,在沿海地区的土体中较为常见。目前对含生物气的非饱和软土固结理论的研究还不多见。本文围绕非饱和土固结研究中的两个难点问题——连续性条件难建立和有效应力公式难确认,而对含生物气非饱和软土的固结理论开展了较为系统和基础性的研究。主要工作有：1)基于应力分担原理,推导并提出了针对不同饱和状态土的有效应力公式；2)提出孔隙流体的压缩系数计算公式,分析讨论了影响的主要因素；3)从质量守恒的角度,推导建立适用于孔隙水非蒸发非凝结情形的土体连续性方程；4)推导建立高饱和度土的一维固结方程,结合Abaqus有限元,分析了高饱和度土的固结特性；求解了固结方程在线性加载下的解析解,与实际工程进行了比较验证；5)将中等饱和度的非饱和土固结压缩过程分为三个阶段：瞬时压缩阶段、气压消散的固结阶段和超孔隙水压消散的固结阶段,提出了固结简化理论；采用有限差分方法分析了气压消散过程的固结特点。主要结论有：1)当在高饱和度土中应用Terzaghi有效应力公式时,会存在微小误差；其中悬浮在孔隙水中的气泡对有效应力公式没有影响。对于气封闭的非饱和土,引入孔隙气弹力的概念。对于气连通土,有效应力等于总应力再加上吸力；吸力在某种程度上可视为一个荷载。2)影响孔隙混合流体压缩系数的主要因素有三：一是饱和度、二是孔隙水压、三是气泡的分散度。3)对于连续性方程的建立,采用质量守恒方程,可以避开了基于体积守恒所带来的种种麻烦。4)高饱和度土固结方程中的固结系数要考虑到孔隙流体压缩性以及饱和度等的影响。其固结压缩特点：一是存在瞬时变形；二是瞬时超静孔隙水压小于所施加的荷载；三是超静孔隙水压消散缓慢,固结完成时间要相对延长。拟合某具体工程孔隙水压力监测值表明：由解析解所作的曲线与现场监测数据吻合得很好,证明本文所建立的高饱和土固结理论是合理和适用的。5)与气压消散固结过程所对应的一维固结方程与Terzaghi固结方程有很大差异,属于完全非线性偏微分方程。对于超孔隙水压消散的固结过程,可忽略孔隙气的质量,单独对孔隙水建立连续性方程。理论分析与文献中的试验数据吻合良好,表明所给出的简化固结分析思路是可行的。本文理清了非饱和土固结研究中的一些基础性问题,为进一步深入研究含生物气非饱和软土的固结问题以及工程性分析应用,打下了较为坚实的理论基础。更多还原

【Abstract】 The undersurface soils are usually regarded as saturated soils. However there are bubbles in these soils as is often the case, e.g., the soils containing biogas distribute widely along the coastal and inshore zones. Nowadays it is scarce for studies on the consolidation theory of unsaturated soft soils containing biogas. The research unfolded in the thesis began from the attempt to solve two difficulties in the consolidation theory of unsaturated soils-one was about continuity condition, the other was about the formula of effective stress. The consolidation theory for unsaturated soils containing biogas in this thesis has been studied systemically and basically.The main contents were as followed:1) Based on the stress-sharing principle, the formulae of effective stress for soils with different saturation degrees were derived and proposed;2) A new expression for the compressibility coefficient of pore fluid was put forward, and the factors which influenced mostly the compressibility were discussed;3) According to the principle of mass balance, the continuity equation for three-phase soils was created, though which was inapplicable to the case of evaporation or condensation of pore water in soils;4) One-dimensional consolidation equation for soils with high degree of saturation was derived, and with the help of Abaqus the consolidation characteristic was analyzed;5) The compression process of unsaturated soils with middle degree of saturation was divided into three stages:instantaneous compression stage, consolidation stage due to the dissipation of pore air pressure, and consolidation stage due to the dissipation of excess pore water pressure. Then a simple consolidation theory was proposed. The characteristic of consolidation relative to the dissipation of pore air pressure was studied by finite difference method.The main conclusions are as follow:1) For nearly-saturated soils, the "real" effective stress would be a little smaller than TERZAGHI’s effective stress. And air bubbles suspended in pore water do not influence the formula’s exactness. For soils in which air phase is discontinuous, a new concept of pore air elastic pressure is put forward. For soils in which air phase is continuous, effective stress is equal to the value of the total stress plus suction. Suction may also be regarded as a type of load to some extent.2) There are three factors which influence mostly the compressibility coefficient of pore mixture fluid. The factors are degree of saturation, pore water pressure and dispersion degree of air bubbles.3) It is complicated to found continuity equation for unsaturated soils because of the uncertain volume of air phase. But when according to the principle of mass balance, the mass of air phase can be neglected. So the continuity equation of three-phase soils can be created compactly.4) The consolidation coefficient of soils with high degree of saturation is influenced mainly by degree of saturation and the compressibility of pore fluid. The compression characteristic of this type soil is as follows:a) there is the instantaneous deformation when compressed; b) the instantaneous excess pore water pressure is smaller than the applied load; and c) the excess pore water pressure dissipates slowly, so that the time needed for this type soil to complete consolidation is extended comparing to the corresponding saturated soil. When studying the monitoring data of pore water pressure in a certain real engineering, the monitoring data fits the analytical solution nicely. It is proved that the consolidation theory of soils with high degree of saturation founded in the thesis is proper and applicable.5) For the consolidation stage due to the dissipation of pore air pressure, the presented equation, not similar to Terzaghi’s consolidation equation, is a type of absolute nonlinear partial differential equation. For the consolidation stage due to the dissipation of excess pore water pressure, the mass of pore air can be neglected. And the consolidation equation is solely about the dissipation of excess pore water pressure. The numerical results from this simplified theory are compared with the experimental results from laboratory tests reported in the literature, and the agreement is good. It can be concluded that the hypothesis is rational and the simplified computation is practical in engineering.In this thesis, some basic and important problems in the consolidation research of unsaturated soils are discussed and carried out. The results obtained from the thesis would be a valuable theoretical foundation for subsequently researching the consolidation of unsaturated soft soils containing biogas and the application on the engineering.更多还原