In this paper, an anisotropic elasto-plastic damage model in strain space has been established to describe the behaviour of geomaterials under compression dominated stress fields and seepage fields. The research work focuses on rate-independent and small-deformation behaviour during isothermal processes. The salient features of geomaterials is fully defined in the starting points:
a second-order "fabric tensor" as the damage internal variable.
an equivalent state based on while the formulation is symmetric with respect to the sign of the stress/strain and
a general free energy function including the mechanisms of damage. plasticity, hydraulic fracturing and damage residual effects. The constitutive relations are developed in the well-established continuum mechanics. An one-parameter damage dependent elasticity tensor deduced based on tensorial algebra and thermodynamic requirements. Finally, the analyses of Kolnbrein arch dam, are presented.
Geomaterials have complex mechanical behavior, such as stress-induced anisotropy, hysteresis, dilatancy, irreversible strain and strongly path dependent stress-strain relations, which is generally associated with the existence of a great deal of micro- and meso-cracks and their propagation. Continuum damage mechanics, which employs some continuum variables to describe the micro-defects, has been an appealing framework for modeling geomaterials, see e.g., Ju (1959),Dragon and Mroz(1979), Dragon (1993), Kawamoto et al, (1988),Ortiz (1985), Zhang (1992) and Stumvoll and Swoboda (1993). In order to fit the complicated behaviour of geornaterials, various starting points and assumptions are adopted in these models, and their formulations are generally sophisticated and have few common points, which have hindered these models from going into practical applications. The key point is that few models can take account of geomaterial features on an appropriate theoretic basis. In this paper, we try to put all salient features of geomaterials only into starting points: the damage variable, equivalent state and free energy function. The constitutive relations. e.g., damage elasticity and damage evolution laws, will be developed in the well-established continuum mechanics without concerning the special features of geomaterials. In this paper the second-order fabric tensor(Oda, 1983: Cowin, 1985), which is a direct geometric measure of material microstructure, is chosen as the damage tensor. Some authors take the mechanical effects caused by damage as the indirect damage measures. For example, Ju (1989) developed the idea to the fullest by taking the fourth-order elasticity tensor as the damage variable. It is noted that the damage effects for geomaterials is significantly dependent on the sign of stress/strain. Thus, the indirect damage variable also becomes stress/strain-dependent, which violates the independent principle of state variables, see Ziegler (1977). In this paper, one-parameter damage-dependent elasticity tensor is formulated by tensorial algebra and thermodynamic requirements. Kawamoto et.al.(I988)defined a damage tensor based on statistical geomaterial data and the hypothesis of strain equivalence (Lemaitre,1971) to establish the damage elasticity. However, it is a very coarse approximation for geomaterials.
