Soil classification terminology – particle size only: What is the name of the soil classification system that categorizes composite soils exclusively on the basis of particle-size distribution (no plasticity indices)?

Introduction / Context:
Different classification systems serve different purposes. Some rely entirely on grain-size distribution, while others incorporate plasticity characteristics. Knowing which system uses only particle-size data helps in preliminary identification and communication among engineers and geologists.

Given Data / Assumptions:

• Composite natural soils may include gravel, sand, silt, and clay fractions.
• The question restricts the basis strictly to particle-size distribution (PSD).

Concept / Approach:
Textural classification (e.g., triangular charts of sand–silt–clay) assigns names based solely on relative proportions of size fractions. It does not use Atterberg limits. By contrast, the Unified Soil Classification System (USCS) combines PSD with plasticity data (plasticity chart). The HRB/AASHTO system also uses both gradation and plasticity for roadwork suitability, not PSD alone. “Particle classification” is a generic phrase rather than a standard system name in practice.

Step-by-Step Solution:

Verification / Alternative check:
Textbook charts for soil texture (sand–silt–clay triangle) label zones like sandy clay loam, silty clay, etc., derived purely from PSD percentages.

Why Other Options Are Wrong:

• USCS and HRB/AASHTO require plasticity data in addition to PSD.
• “Particle classification” lacks a recognized standard definition as a system name.

Common Pitfalls:
Assuming USCS is PSD-only; ignoring that plasticity controls whether fines are silt or clay in USCS.

Final Answer:
Textural classification