In soil mechanics and geotechnical engineering, the slow recovery of structural strength in remoulded clay due to an isothermal gel–soil–gel transformation (after agitation and subsequent rest) is known as which property?

Introduction / Context:
Clays exhibit time-dependent behavior influenced by their microstructure and pore-fluid chemistry. When a clay is remoulded, its structure collapses and undrained shear strength drops. Over time at constant temperature and moisture, some strength can recover due to structural reformation—an important concept for construction staging and stability assessments.

Given Data / Assumptions:

• Material: clayey soil.
• Process: agitation/remoulding followed by rest at roughly constant temperature (isothermal).
• Observation: partial strength recovery with time.

Concept / Approach:

The term for this reversible, time-dependent decrease in apparent viscosity/strength under shear and recovery at rest is thixotropy. In soils, thixotropy is linked to rearrangement and flocculation of clay particles and the rebuilding of the diffuse double layer, which restores some interparticle bonding.

Step-by-Step Solution:

Verification / Alternative check:

Field vane tests comparing peak and remoulded strengths often show increased strength after waiting periods, consistent with thixotropic gain.

Why Other Options Are Wrong:

• Isotropy/anisotropy: Directional properties, not time-dependent recovery.
• Allotropy: Applies to elements with different structural forms, not soils.
• Rheopexy: Strength increases with continued shear (opposite behavior).

Common Pitfalls:

• Confusing consolidation (drainage/time) with thixotropy (structure/time at constant water content).

Final Answer:

Thixotropy