A STUDY ON THE RHEOLOGICAL MODEL OF POROUS MEDIA
多孔介质的流变模型研究

Porous media are a special kind of material, which consists of skeleton particles and pores between. Pores are usually saturated with one or several kinds of fluids. Normally, porous media suffer both an outer stress (total stress) and an inner stress (pore pressure or fluid pressure) simultaneously. So, an effective stress is necessary in the study of deformation behavior of porous media. The effective stress is an equivalent stress, which alone yields the same strain behavior with the two stresses applying on porous media outside and inside. K.Terzaghi proposed the first effective stress of porous media for soil mechanics in 1923, which is the simple difference between the outer stress and the inner stress. The Terzaghi effective stress concept is widely used not only in soil mechanics but also in rock mechanics. However, a recent research discovered that porous media have two effective stresses: the Primary effective stress and the Structural effective stress, named as the Double Effective Stresses of porous media. Actually, the Terzaghi effective stress is only an approximation to the structural effective stress.Corresponding to the Double Effective Stresses, porous media have two kinds of deformation mechanism: the elastic deformation (the Primary deformation) and the viscous deformation (the Structural deformation), which is related to the special material structure of porous media. The primary effective stress yields elastic strain in porous media while the structural effective stress yields viscous strain. The total strain of porous media is the sum of elastic strain and viscous strain. The rheological model to calculate the total strain of porous media must adopt both the primary effective stress and the structural effective stress(the double effective stresses) for the calculations of elastic strain and viscous strain respectively. However, the conventional rheological model adopts the Terzaghi effective stress alone to calculate the two kinds of strain, which cannot fit the strain behavior of porous media properly. The new model with double effective stresses, proposed in this paper, can simulate practical strain behavior of porous media and also unite porous media and solids through property parameters.