The following results were obtained from CU tests on a clay soil that is the foundation material for an embankment.

σ, (kPa) : 300 400 600
σ₁-σ₂ (kPa) : 331 420 487
∆u (kPa) : 111 160 322

(a) Determine the total and effective principal stresses for all three tests (You may summarize them in a table).
(b) Recommend the shear strength parameters to be used for short-term and long-term analyses. The maximum confining pressure (cell pressure) at the depth of interest is 300 kPa.