3.2.4 Triaxial tests on a saturated clay

Product: ABAQUS/Standard  

This example is a simple demonstration of the modified Cam-clay plasticity model provided in ABAQUS. Cam-clay theory provides a reasonable match to the experimentally observed behavior of saturated clays and belongs to the family of critical state plasticity models developed by Roscoe and his colleagues (see Roscoe and Burland—1968—and Schofield and Wroth—1968).

The Cam-clay model in ABAQUS permits two extensions of the original Roscoe model: “capping” of the yield ellipse on the wet side of critical state, and consideration of the third stress invariant in the yield function. Both of these extensions to the modified Cam-clay theory are documented in Plasticity for non-metals, Section 4.4 of the ABAQUS Theory Manual. They are both included in this example.

The general modified Cam-clay yield function used in ABAQUS is

where the three stress invariants are the equivalent pressure stress given by

the equivalent shear stress given by

where is the deviatoric stress (); and the third stress invariant,

The other parameters in the function are a, the value of the equivalent pressure stress at critical state; M, a material parameter defining the slope of the critical state lines; , a “capping” parameter used to provide a different shaped yield ellipse on the wet side of critical state; and g, a function that is dependent on the third stress invariant, used to define different yield surface sizes in compression and extension:

where K is a material parameter.

The “standard” Cam-clay yield function has 1. Including these parameters in the yield surface expression generalizes that expression to allow closer matching of data under various conditions of loading.

Problem description

Results and discussion

Input files

References

Figures

Figure 3.2.4–1 Triaxial test with smooth platens.

Figure 3.2.4–2 Yield surface profiles for triaxial compression solutions.

Figure 3.2.4–3 Modified Cam-clay plasticity response.

Figure 3.2.4–4 Yield surface profiles for triaxial extension solutions.