THE INFLUENCE OF INTERFACES ON THE STRESS STATE IN UNSATURATED SOILS
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摘要: 非饱和土是一种三相多孔介质，不同相之间的交界面尤其是气液交界面的存在直接影响了非饱和土的宏观行为.首先对土中交界面的形式和作用进行了探讨，指出气液交界面对非饱和土的行为有重要影响，并给出了界面功和气液比表面积的表达式.在已有的非饱和土变形功表达式基础上，引入界面能影响，得到了考虑交界面影响的非饱和土自由能方程.利用所得的自由能方程，给出了考虑交界面影响的非饱和土固相和液相相应的应力变量.对考虑交界面面积的液相流动方程进行了探讨，给出了非平衡条件下的土水特征曲线表达式，指出在平衡条件下土水特征曲线中应当考虑交界面面积的影响，传统土水特征曲线是三维关系在吸力-饱和度平面上的投影.将比表面积与土水特征曲线的关系，利用已有试验数据验证了该表达式的合理性.利用界面面积的表达式计算有效应力，将其与已有试验结果进行对比，表明给出的比表面积表达式可很好地反映实际情况.不同于已有现象学研究，本文推导具有严格的理论基础，研究表明完整的有效应力表达式中应考虑土体内部作用力的影响，其不仅包含基质吸力，同时还包含其他形式的作用力，其大小与界面比表面积有关.该表达式为下一步研究界面效应对土体变形、强度和流动特性的研究提供了基础.Abstract: Unsaturated soil is a three-phase porous media. The interfaces between every two phases, especially between liquid and gas phase, have important influence on soil behavior. The interfacial form and effect of soil are discussed and the expressions for interfacial work and specific interfacial area are presented. By introducing the interfacial work into the existing work input equation, the Helmholtz free energy of unsaturated soils with interfacial effect can be derived. Based on the free energy equation, the stress variables considering interfacial effect for solid and liquid can be obtained. The influences of interfacial area on flow equation of liquid phase are discussed, and it is pointed out that the gas-liquid interface area should be introduced as a third variable in a complete soil water retention curve (SWRC). The traditional SWRC is a projection of the three-dimensional expression in the (s, Sr) plane. The effective stress considering specific area can be calculated by the relationship between specific area and SWRC. The proposed equation of effective stress is used to simulate experimental data in the literature, and results show our findings are in good accordance with practice. Different from the existing phenomenology studies, the deductive process has a rigorous theoretical basis in this paper. The results shown that the complete expression of effective should consider the effects of internal force in soil, which including not only matric suction, but also the other force related to the specific interfacial area.
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Key words:
- unsaturated soils /
- effective stress /
- specific interfacial area
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图 1 比表面积与饱和度关系示意图
Figure 1. Sketch for relationship between specific interfacial area and degreeof saturation
图 3 比表面积与饱和度关系
Figure 3. Relationship between specific interfacial area and saturation
图 4 比表面积、饱和度与毛细力三维关系的预测结果
Figure 4. Predictions for relationship among specific interfacial area, saturation and capillary pressure
图 5 吸应力的对比结果
Figure 5. Comparison between predicted results and experimental data for suctionstress
图 6 饱和度和有效应力参数
Figure 6. Predictions for degree of saturation and effective stress parameter
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