Name the property: The ability of a soil to undergo rapid deformation without rupture, without elastic rebound, and with accompanying volume change is termed:

Introduction / Context:
Fine-grained soils display time-dependent and moisture-dependent deformation behaviors. Identifying the property that allows permanent deformation without cracking or spring-back is central to compaction, rolling, and earthwork handling practice.

Given Data / Assumptions:

• Soil is cohesive with significant fines (clays/silts).
• Load is applied such that deformation occurs at near-constant volume or with volume change.
• We are distinguishing fundamental index properties.

Concept / Approach:

Plasticity is the property enabling a soil to be remolded without rupture and without significant elastic recovery once the load is removed. It is quantified indirectly by Atterberg limits and correlates with clay mineralogy and water content. Porosity is a volumetric ratio; permeability describes fluid flow; ductility is a metals term; thixotropy involves time-dependent strength recovery, not the immediate deformation property described.

Step-by-Step Solution:

Verification / Alternative check:

High-plasticity clays (CH) exhibit large plastic ranges and molding capability; sands have negligible plasticity.

Why Other Options Are Wrong:

(a) Porosity is a static ratio; (c) Permeability concerns seepage; (d) Ductility suits metals; (e) Thixotropy is a delayed structural rebuilding phenomenon.

Common Pitfalls:

Confusing plasticity with viscosity or with thixotropic behavior; assuming plasticity implies constant volume (it does not).

Final Answer:

Plasticity