Constitutive approach for rate‐sensitive anisotropic structured clays

Abstract

SUMMARYThis paper describes a constitutive approach to model the behavior of rate-dependent anisotropic structured clay. Rate-sensitivity is modeled using overstress viscoplasticity. Clay structure is treated as a viscous phenomenon whereby the viscosity of the undisturbed structured clay is initially very high and the viscosity degrades or decreases with plastic straining until the intrinsic or residual viscosity is reached. A microstructure tensor approach is used to make the structured viscosity anisotropic; whereas, the intrinsic viscosity is assumed to be isotropic. The behavior of the constitutive model is compared with the measured response of two clays (Gloucester and St. Vallier clay) from Eastern Canada during triaxial compression tests on specimens trimmed at different orientations to the vertical. The comparisons show that the constitutive framework is able to describe the anisotropic and rate-sensitive response of both clays. The response of the model is also examined for the more general case of anisotropic consolidated triaxial compression and extension.

Performance of a reinforced embankment on a sensitive Champlain clay deposit

“…The Hinchberger and Qu (2009) According to Perzyna's (1963) overstress theory of viscoplasticity, the governing 93 equation can be expressed in terms of strain-rate tensor: 94…”

“…where S ij is deviatoric stress; G is shear modulus; ı ii is summation of the principal stresses; K is 96 bulk modulus; Ȗ vp (İ d ) is the state-dependent viscoplastic fluidity parameter (to be discussed in the 97 following subsection) and Ø(F) is a flow function that can be expressed in term of overstress as: 98 The state-dependent fluidity concept introduces a new parameter, Ȧ o , to mathematically define 111 the structure of the soil (Hinchberger and Qu 2009 plastic shear strain, respectively. A is a weighting parameter, which is assumed to be 0.5 similar 120 to Baudet and Stellebrass (2004).…”

“…A is a weighting parameter, which is assumed to be 0.5 similar 120 to Baudet and Stellebrass (2004). Finally, the exponential damage law is introduced to describe 121 rate of soil structure degradation (Hinchberger and Qu 2009), expressed as: 122 …”

“…Full details regarding 84 the derivation of the constitutive model, the state dependent fluidity parameters concept and the 85 damage law are given by Hinchberger andQu (2009) andQu (2008). 86…”

“…All the 213 constitutive soil parameters are summarized in Table 2. The stress-strain behaviour predicted by 214 axisymmetric finite element analysis using state-dependent viscoplastic parameter model 215 (Hinchberger and Qu 2009) is shown in Fig. 6.…”