- 2073 Magh · 3 marks
Triaxial drainage conditions in the field
Short answer
UU test represents rapid loading on saturated clay with no drainage, like end-of-construction stability. CU test models consolidation under existing load followed by sudden loading, such as rapid drawdown. CD test corresponds to slow loading or long-term conditions where excess pore pressure has dissipated, applicable to sands and long-term clay stability.
How are the drainage conditions adopted in a triaxial shear test realized in the field?
The three triaxial tests represent three field situations, depending on how fast the load is applied compared with the rate at which water can drain from the soil.
| Triaxial test | Drainage in test | Field condition it represents |
|---|---|---|
| UU (unconsolidated undrained) | No consolidation, no drainage during shear | Rapid loading on saturated clay of low permeability, with no time for pore pressure to dissipate: end of construction of an embankment or foundation on soft clay, rapid excavation. Short-term stability. |
| CU (consolidated undrained) | Consolidated under , no drainage in shear | Soil first consolidated under the existing load, then loaded suddenly: rapid drawdown in an earth dam after long seepage; embankment raised in stages; sudden loading after consolidation. |
| CD (consolidated drained) | Consolidated and sheared with drainage open, so | Slow loading, or a long time after construction when the excess pore pressure has dissipated: long-term stability of cuts, slopes and embankments, and loading of sands and gravels. |
Key idea: clays under quick loading behave undrained (UU), clays under slow loading behave drained (CD), and sands drain quickly, so they are almost always treated as drained.
✓ Answer checked by Claude Opus 5.5 (high effort)
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