ABSTRACT
Suction theory is the core of the unsaturated soil mechanics theory as well as the difficulty. The matrix suction of the soil reflecting water absorbing capacity, which is widespread used currently, representing the interaction between soil particle and pore water rather than the interaction between soil particles, is not in conformity with the principle of effective stress of soil. To get rid of this
that the existing effective stress principle and shear strength theory of unsaturated soil in the study of unsaturated soil nature cannot succeed, there are two essential reasons: (1)mistakenly believe that the matrix suction is equivalent to wet suction; (2) it is failed to realise that the suction of unsaturated soil is composed of wet suction and structure suction. Structural characteristics of unsaturated soils are usually obvious, so structure suction should not be ignored due to the structural of soil in the study of unsaturated soil mechanics characteristics, especially the particularity in unsaturated soil such as loess, red clay and expansive soil. The structure suction proposed by the author is the characterization of tensile stress between soil particle, mainly includes the cementation force, dipole force, magnetic force, surface force (electric double layer suction) and ion-electrostatic force, etc., is influenced by soil water content, the particle composition and arrangement, the chemistry of pore solution, etc., but the degree of each force affected varies. According to the fact that whether structure suction is affected by the change of water content, the structure suction can be divided into intrinsic structure suction and variable structure suction[3].
