Effective stress is a fundamental concept of the mechanics of porous media, through which the theory of solid mechanics is applied to porous media. However, the effective stresses proposed by different researchers are quite different, which brings about uncertainty to the application of effective stress. Three typical effective stress approximations have been proposed so far. These are Terzaghi’s effective stress, Biot’s effective stress and dual effective stresses. Terzaghi’s effective stress was the first concept of effective stress proposed for soil, which brought about the birth of soil mechanics. Terzaghi’s effective stress is only applicable to extremely loose material and is not applicable to the study of the mechanical performance of tight media.Biot’s effective stress is a modification to Terzaghi’s effective stress. Because Biot’s coefficient has no clear physical meaning and usually takes empirical values, Biot’s effective stress equation is only an empirical equation. Dual effective stresses are proposed based on the deformation mechanism of porous media. There are two basic types of deformation for porous media: primary deformation and structural deformation, and correspondingly, there are two effective stresses for porous media. These are the primary effective stress and the structural effective stress. The primary effective stress determines the primary deformation of porous media, and the structural effective stress determines the structural deformation of porous media. Dual effective stresses take in account the physical properties of porous media and take the physical parameters of porous media into the formula, which can be applicable to different media as the physical parameters take different values. The concepts of new dual effective stresses proposed by Dr Mao are loosely defined and are scientifically weak, and they cannot pass practical tests. For example, the pore compressibility of porous media is not negatively but positively correlated with porosity.
LI Chuanliang, ZHU Suyang. Discussion of dual effective stresses in porous media—Analysis on the paper of Re-recognition of dual effective stresses and the comprehensive effect. Petroleum Science Bulletin, 2019, 04: 414-429.
