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1

Structure and calibration of constitutive equations for granular soils

Sawicki A., Sławińska J., Mierczyński J.

Studia Geotechnica et Mechanica

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2014

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Vol. 36, nr 4

35--46

EN

The form of incremental constitutive equations for granular soils is discussed for the triaxial configuration. The classical elasto-plastic approach and the semi-empirical model are discussed on the basis of constitutive relations determined directly from experimental data. First, the general structure of elasto-plastic constitutive equations is presented. Then, the structure of semiempirical constitutive equations is described, and a method of calibrating the model is presented. This calibration method is based on a single experiment, performed in the triaxial apparatus, which also involves a partial verification of the model, on an atypical stress path. The model is shown to give reasonable predictions. An important feature of the semi-empirical incremental model is the definition of loading and unloading, which is different from that assumed in elasto-plasticity. This definition distinguishes between spherical and deviatoric loading/unloading. The definition of deviatoric loading/unloading has been subject to some criticism. It was therefore discussed and clarified in this paper on the basis of the experiment presented.

2

3D and 2D Formulations of Incremental Stress-Strain Relations for Granular Soils

Sawicki A.

Archives of Hydro-Engineering and Environmental Mechanics

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2008

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Vol. 55, nr 1-2

45-53

EN

3D formulation of incremental relations, describing pre-failure deformations of granular soils, is presented. The starting point are respective equations formulated previously for the axi-symmetrical configuration, as that in the tri-axial apparatus. These relations, proposed for particular configuration, are generalized in the form of tensor equations for the strain increments. Similarly, the loading/unloading criterion and the instability line have been generalized for 3D conditions. A kind of cross-isotropy of granular soil is taken into account. Then, the incremental stress-strain relations for the plane strain state are re-derived from general equations, as such conditions are most often used for simulations of practically important problems. The procedure proposed in this paper is practically oriented, as the soil parameters can be determined just from the tri-axial tests.

3

A Study on Pre-Failure Deformations of Granular Soils

Sawicki A.

Archives of Hydro-Engineering and Environmental Mechanics

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2007

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Vol. 54, nr 3

183-206

EN

A simple model describing pre-failure deformations of granular soils is derived on the basis of a wide range of experimental data. The model is defined by two incremental equations describing the volumetric and deviatoric strains. Functions appearing in governing equations were determined from experiments performed in the triaxial apparatus, with additional measurements of lateral strains for some simple stress paths. These functions are different for loading and unloading, and have different shapes for contractive and dilative soil samples. The instability line is built into the structure of the model. The incremental equations were applied to predict the soil behaviour during anisotropic compression, including determination of the K0-line. Some basic statistical characteristics of the initial density index of investigated soils and deformations during isotropic compression are presented.