Soil classification systems used for general engineering purposes: Which classification is most widely adopted across geotechnical engineering projects for general (non-highway-specific) use?

Introduction / Context:
Soil classification provides a common language for communicating properties and probable behavior. For general civil works, the Unified Soil Classification System (USCS) is the de facto standard integrated into many codes, specifications, and boring logs.

Given Data / Assumptions:

• General civil engineering applications (foundations, excavations, earthworks).
• Both coarse- and fine-grained soils appear in projects.
• Laboratory tests include Atterberg limits and grain-size distribution.

Concept / Approach:
USCS classifies soils based on percent fines, plasticity (LL, PL), and gradation, producing groups like GW, GP, SW, SP, ML, CL, etc. It uses plasticity charts and coefficients of uniformity/curvature to distinguish well-graded vs poorly graded soils and plastic vs non-plastic fines. HRB/AASHTO is prevalent for pavements; textural and particle-size systems are descriptive but less predictive of engineering behavior.

Step-by-Step Solution:

Verification / Alternative check:
Most borehole logs and lab reports worldwide use USCS group symbols; agency specifications often require USCS alongside AASHTO when relevant.

Why Other Options Are Wrong:

• A/B: Useful descriptively but not standardized for design decisions across all soil types.
• C: HRB/AASHTO is highway-focused.
• E: RMR is for rock masses, not soils.

Common Pitfalls:
Confusing USCS with AASHTO; forgetting dual symbols (e.g., GW-GM) when borderline fines are present.

Final Answer:
Unified Soil Classification System (USCS)