Comparative Study Of Hypoplastic Constitutive Model With Elastoplastic Constitutive Model For Sands

Hypoplastic constitutive theory is a new theory. Studies have shown that hypoplastic theory is more suitable for the simulation of stress-strain relation for soils than elastoplastic theory. Research on hypoplastic theory has important significance for the development of constitutive model for soils. Gudehus-Bauer hypoplastic model is studied by using Matlab as a tool in this paper. The specific research work can be summarized as follows:(1) Based on the analysis of density factor and relative tests, the physical meaning of initial critical void ratio is discussed. A formula to obtain this parameter is proposed. The value of initial critical void ratio obtained by the proposed formula is very close to that by the experiment.(2) Referring to the critical state line, the mechanical behavior of Gudehus-Bauer hypoplastic model under triaxial stress conditions is simulated by using Matlab. Gudehus-Bauer hypoplastic model can reflect the critical state lines proposed by Cambridge model very well.(3) The development law of elastic and plastic strain for sands in monotonic loading process simulated by Gudehus-Bauer hypoplastic model is studied. The effects of different initial critical void ratio on elastic strain is studied too. The results shows that elastic strain stop increasing at almost the same axial strain for the same kind of sands with different initial critical void ratio.(4) The general expression of failure criterion implied within Gudehus-Bauer hypoplastic model(G-B failure criterion) is derived. G-B failure criterion can adopt the different values of friction angle under triaxial compression and triaxial extension stress state in the same time to consider the effects of the different friction angles on soil destruction. The general expression of G-B failure criterion is very similar with the general expression of extended Mises criterion. While the shape and size of G-B failure criterion in the principal stress space is very close to Lade-Duncan failure criterion. With the increase of critical friction angle,the contour line in the ? plane of G-B failure criterion becomes slightly concave from convex. The failure criterion with concave contour line reflect the characteristics of sand as unstable material.