非饱和土有效应力方程的试验验证

The skeleton, pore water and pore air of a soil are respectively taken as independent objects for internal forces equilibrium analysis by applying continuum mechanics method. And the equilibrium equation of each phase in the soil is obtained by taking the free bodies to carry out internal force analysis and considering the effects of pore fluid pressure and other external loads acting on the soil skeleton separately. In this way the effective stress equation for unsaturated soils can be obtained. Moreover,it shows that the effective stress is the skeleton stress caused by the action of external loads excluding pore fluid pressure, and that the formula of effective stress is unified for both saturated and unsaturated soils. It can be found that the effective stress equation is the same as the expression of the combined stress in the shear strength formula proposed by Vanapalli and Fredlund in 1996 according to their experiment results. So, it can be proved that the shear strength of unsaturated soils is governed by effective stress. In order to verify that the deformation of unsaturated soils is also governed by the effective stress, a series of special instruments have been developed for unsaturated soil tests. Meanwhile in this project, drying and shrinking test, confined compression test and triaxial test are designed for clay. The validity of the effective stress equation for unsaturated soils will be verified by comparing the test results to those of theory or those of tests for saturated soils. In the triaxial test, the stress and strain character test of the clay will be combined with numerical simulation of the deformation of the sample and the distribution of water content. To propose and verify the effective stress equation for unsaturated soils is significant to the development of soil mechanics, especially for building a unified theoretical frame of soil mechanics for saturated and unsaturated soils.

应用连续介质力学方法，分别把土骨架、孔隙水和孔隙气作为独立的研究对象。通过隔离体受力分析,分开考虑孔隙流体压强和其它外力对土骨架的作用得到每一相的平衡微分方程。由此得到非饱和土的有效应力方程，证明了有效应力就是不包含孔隙流体压强的所有其它外力作用产生的土骨架应力。饱和土与非饱和土的有效应力是统一的。它与Vanapalli和Fredlund根据试验提出的非饱和土抗剪强度公式中的应力表达式相同，说明非饱和土的抗剪强度取决于有效应力。为了验证非饱和土的变形也取决于有效应力，申请者研发了测试仪器，拟开展非饱和粘土的开裂试验、侧限压缩和三轴试验，将试验结果与理论结果或与饱和土试验结果的对比验证有效应力方程的适用性。其中三轴试验采用土样变形数字图像测量系统，并将土样变形和含水量分布的数值模拟与试验测量结合起来。. 提出并验证非饱和土的有效应力方程，对建立非饱和土力学理论体系，对土力学学科发展有重要意义。.

首次提出土骨架水的概念，将土分成饱和土、非饱和土和干土。明确了有效应力的物理意义，完善和修正了有效应力原理。分离考虑孔隙流体压强和其它外力的作用，分别采用分相平衡方程、粒间力分析、土体断面内力分析、外力土骨架应力的定义、现有的孔隙介质力学平衡方程等5种方法推导出非饱和土的有效应力方程，从理论上说明有效应力是不包含孔隙流体压强的所有其它外力作用产生的土骨架应力，是控制土骨架的强度和变形的应力。为了验证非饱和土的有效应力方程，重新设计研制了非饱和土三轴试验仪、非饱和土土水特征曲线和导水系数联合测定仪、改制了高压固结仪、搭建了环刀土样干燥收缩试验装置。开展了硅微粉、桂平粘土、高岭土、尾矿砂与高岭土的混合土的土水特征曲线、导水系数、直接剪切和三轴压缩试验，同时引用他人的非饱和土抗剪强度和变形试验结果，通过对试验资料进行重新分析，证明了无论在饱和还是非饱和条件下，当孔隙流体压强作用对土的抗剪强度和变形的影响可以忽略时，土的有效应力是决定其强度和变形的应力。此外还开展了非饱和土导水系数的研究。. 本研究明确了有效应力的物理意义，确立了土力学和孔隙介质力学的统一的有效应力方程，修正和完善了有效应力原理。鉴于有效应力对土力学和岩土工程的重要性，研究成果对土力学和岩土工程学科的发展具有重要意义。将有助于建立饱和与非饱和土统一的土力学理论体系，对于解决非饱和条件下的岩土工程问题具有理论意义和实际应用价值。在本项研究中出版英文专著1部、发表学术论文15篇、申请国家发明专利7项（已授权2项）、国际发明专利1项，软件著作权2项。参加与非饱和土相关的学术会议10次并做学术报告，承办相关的学术研讨会2次。邀请国内外知名专家学术交流4次。结合本项目发展的土样变形数字图像测量方法和研制的非饱和土试验仪器，如非饱和土三轴试验仪、导水系数和土水特征曲线联合测定仪、土样干燥收缩试验装置等均已经实现成果转化，可以推广应用。