Field identification of plasticity in fine soils Which simple field/hand tests are used collectively to assess the plasticity of fine-grained soils during reconnaissance?

Introduction / Context:
Before laboratory index testing, practitioners often perform quick field tests to gauge plasticity and to distinguish silt from clay fractions. These tactile tests support sampling decisions and preliminary classification according to engineering behavior.

Given Data / Assumptions:

• Moisture content appropriate for performing the tests.
• Representative fine-grained soil sample.
• Experienced observer interpreting responses.

Concept / Approach:

The dry strength test evaluates the resistance of an oven-dry pat to crumbling, indicative of clay content and bonding. The toughness test rolls threads near the plastic limit and notes resistance and recoverability, reflecting plasticity index. The dilatancy test (shaking test) observes the quick sheen response for silts; clays typically lack this rapid water “blinking.” Together, these provide a qualitative yet effective plasticity assessment.

Step-by-Step Solution:

Verification / Alternative check:

Results correlate with Atterberg limits from laboratory testing, offering confidence for preliminary classification (e.g., USDA/ASTM procedures).

Why Other Options Are Wrong:

Each listed test contributes unique information; omitting any reduces diagnostic power. “None” contradicts established practice.

Common Pitfalls:

Over-reliance on one test; performing tests at inappropriate moisture contents; misinterpreting dilatancy in very fine sands.

Final Answer:

All of these.