While both consolidated undrained (CU) and consolidated drained (CD) tests can determine a soil sample’s effective stress parameters, the CU test is often preferred for several reasons:
Shorter Testing Duration: CU tests generally take less time than CD tests. This is because CD tests require complete dissipation of excess pore water pressure during testing, which can be time-consuming for soils with low permeability. In contrast, CU tests do not require this dissipation, leading to faster results.
Stress Path Insights: The stress path generated during a CU test provides valuable information about the soil’s behavior under undrained loading conditions. This data is particularly useful for analyzing the stability of structures like embankments and slopes, where rapid loading or undrained conditions are prevalent.
Lower Stress Level Failure: CU tests typically induce failure at a lower stress level compared to CD tests. This is due to the undrained condition, where pore water pressure cannot dissipate, leading to a faster increase in effective stress and earlier failure. This information is relevant for designing structures that may experience sudden loading or undrained conditions.
In conclusion, while both CU and CD tests have their merits, the CU test’s shorter duration, valuable stress path data, and lower stress level failure make it a preferred choice for many geotechnical engineers, especially when dealing with projects involving rapid loading or soils with low permeability.