Whitlow’s answer (paraphrased): You are likely ignoring sample disturbance. Even a 1 mm change in diameter during extrusion changes the stress path. Run a consolidation stage first, and plot the results as p'-q space (mean effective stress vs. deviator stress), not just principal stresses. Whitlow includes a diagnostic checklist for "bad" test curves.
Overview: The failure criteria of soil under stress. roy whitlow basic soil mechanics
Whitlow’s answer: That depends on the soil’s permeability (k) and the drainage path length (H). He introduces the time factor (Tv) and consolidation theory: 5.3 Seepage Theory:
This is the mathematical heart of Whitlow’s early chapters. He introduces the "phase diagram"—a box split into air, water, and solids. 5.2 Determination of Permeability:
Overview: How water moves through soil masses.
ES
DE
FR
CN