CALCULATED STRESS–STRAIN RESPONSE
Drained Compression Tests:
1. Determine the mean effective stress and the deviatoric stress at initial yield, that is, p9y and qy, by fi nding the coordinates of the intersection of the initial yield surface with the effective stress path. For a CD test,
where no is the slope of the ESP and M 5 Mc. For the standard triaxial drained test, no 5 3.
2. Calculate the mean effective stress and deviatoric stress at failure using Equations .
3. Calculate G using Equation. Use an average value of pr 3 pr 5 1pro 1 pry 2 /24 to calculate G if Equation is used.
4. Calculate the initial elastic volumetric strain using Equation and initial elastic deviatoric strain using Equation .
5. Divide the ESP between the initial yield stresses and the failure stresses into a number of equal stress increments. Small increment sizes (,5% of the stress difference between qf and qy) tend to give a more accurate solution than larger increment sizes. For each mean effective stress increment up to failure:
6. Calculate the preconsolidation stress, p'c, for each increment; that is, you are calculating the major axis of the ellipse using Equation .
7. Calculate the total volumetric strain increment using Equation .
8. Calculate the plastic volumetric strain using Equation .
9. Calculate the plastic deviatoric strain increment using Equation.
10. Calculate the elastic deviatoric strain increment using Equation .
11. Add the plastic and elastic deviatoric strain increments to give the total deviatoric strain increment.
12. Sum the total volumetric strain increments (εp).
13. Sum the total deviatoric shear strain increments (εq).
14. Calculate
15. If desired, you can calculate the principal effective stresses for axisymmetric compression from
The last value of mean effective stress should be about 0.99p9f to prevent instability in the solution