粒间应力、土骨架应力和有效应力

有效应力的概念和有效应力原理对于土力学具有奠基性的意义。但对于诸如"有效应力是虚拟的应力还是真实应力","有效应力方程是否需要修正"等问题在土力学界一直存有争议,尚没有形成共识。在明确有效应力就是不包含孔隙流体压强作用的土骨架应力的基础上,由土颗粒间力的平衡分析和土骨架单元体的平衡分析得到有效应力与总应力以及孔隙流体压强关系的表达式。对于饱和土,这一表达式就是Terzaghi的有效应力方程。表明Terzaghi的有效应力是真实的物理量,具有明确的物理意义,Terzaghi的有效应力方程不需要做任何修正。文中阐明了有效应力、粒间应力和土骨架应力的物理意义及其相互关系。说明在分离考虑孔隙流体压强作用的情况下,有效应力、粒间应力和土骨架应力三者可以是一致的,即不包含孔隙水压强作用的粒间应力和土骨架应力就是有效应力。土骨架应力可以分成孔隙流体压强产生的土骨架应力和有效应力两部分,两者都对土体的变形和强度有贡献,但是作用效果不同。在孔隙流体压强作用对土体的变形和强度的贡献可以忽略的条件下,有效应力决定土的变形和强度。

Intergranular stress,soil skeleton stress and effective stress

The concept and principle of effective stress are significant to the development of soil mechanics. However, some problems such as “Is the effective stress the virtual or real stress?” and “Whether Terzaghi’s effective stress equation needs to be modified or not?” have long been considered to be controversial issues, and there is no consensus up to now. According to the definition that the effective stress is the skeleton stress due to all the external forces excluding pore water pressure, the relationship among the total stress, skeleton stress and pore water pressure can be obtained through the equilibrium analysis of intergranular force and free body of the soil skeleton. Then it may be seen that the expression of the relationship is the Terzaghi’s effective stress equation for saturated soils. It indicates that the Terzaghi’s effective stress is a real physical quantity and has a definite physical meaning. The Terzaghi’s effective stress equation is valid with no necessity to be modified. Moreover, the physical meaning and mutual relations of effective stress, intergranular stress and skeleton stress are clarified in this paper. It indicates that considering the effects of pore water pressure separately, the intergranular stress and the skeleton stress are the same as the effective stress. On the other hand, the skeleton stress can be divided into two components: one is that due to pore fluid pressure and the other is effective stress. They both contribute to the strength and deformation of a soil but play different roles. When the effect of the skeleton stress due to pore fluid pressure on the strength and deformation of a soil can be neglected, changes in the volume and shear strength of a soil are due exclusively to the ones in the effective stress.