Application of UU, CU, CD tests

UU test (unconsolidated undrained)

• Gives $c_u$ with $\phi_u \approx 0$ for saturated clay.
• Used where loading is fast and the clay has no time to drain: stability of foundations and embankments on soft clay at the end of construction, bearing capacity in the short term, and temporary excavations in clay.

CU test (consolidated undrained)

• Gives $c_{cu}$ and $\phi_{cu}$ (total stress) and, with pore pressure measurement, $c'$ and $\phi'$ (effective stress).
• Used where soil is first consolidated and then loaded quickly: rapid drawdown of an earth dam after steady seepage, stage-constructed embankments, and sudden loading of already-consolidated clay under a structure.

CD test (consolidated drained)

• Gives $c_d$ and $\phi_d$ (about equal to $c'$, $\phi'$).
• Used for long-term stability when excess pore pressure has dissipated: natural slopes and cuttings, retaining walls and drained foundations, and for sand and gravel, which drain quickly.