Triaxial and shear testing — when drainage is permitted during the application of the initial (consolidation) cell pressure only, allowing full primary consolidation before undrained shearing, the test is called:

Introduction / Context:
Laboratory shear tests on soils are classified by whether drainage is permitted during consolidation and/or during shear. Correctly identifying the test type is crucial for interpreting the measured strength parameters for design under corresponding field drainage conditions.

Given Data / Assumptions:

• Drainage is allowed while the initial normal (cell) stress is applied so that primary consolidation is completed.
• During subsequent shearing, drainage is not allowed (undrained shear stage).
• Pore pressures during shearing may be measured to convert total to effective stresses.

Concept / Approach:

In a consolidated undrained (CU) test, the specimen is first consolidated under the cell pressure with drains open, permitting volume change and dissipation of excess pore pressure. Then, with drains closed, the specimen is sheared undrained, generating pore pressure changes that can be recorded. This test captures short-term (undrained) strength after the soil has adjusted to the in-situ consolidation stress, which often represents field loading scenarios such as rapid construction on clays.

Step-by-Step Solution:

Verification / Alternative check:

Contrast with UU (no drainage during consolidation or shear) and CD (drainage during both stages). The stated condition matches neither UU nor CD, confirming CU.

Why Other Options Are Wrong:

UU allows no drainage throughout; CD permits drainage throughout; ring shear refers to a different apparatus and boundary condition.

Common Pitfalls:

Confusing CU with CD when volume change is observed during consolidation; forgetting to measure pore pressure, which limits effective-stress interpretation.

Final Answer:

consolidated undrained test (CU)