Soil Classification - Concept Map
Soil Classification Systems and Parameters
Related concepts
Grain-Size Distribution
Sub concepts
- Gradation curve
- Effective size (D₁₀)
- Uniformity coefficient (Cᵤ)
- Coefficient of curvature (Cᶜ)
- Well-graded vs poorly graded
Relationship to central
Foundation for understanding soil behavior and gradation assessment
Atterberg Limits and Plasticity
Sub concepts
- Liquid limit (LL)
- Plastic limit (PL)
- Shrinkage limit (SL)
- Plasticity index (PI)
- Plasticity chart
- A-line classification
Relationship to central
Defines behavior of fine-grained soils under varying moisture conditions
USCS (Unified Soil Classification System)
Sub concepts
- Coarse-grained soils (>50% retained on #200)
- Fine-grained soils (≥50% passing #200)
- Gravel and Sand groups
- Silt, Clay, and Organic groups
- Modifiers: W/P (well/poorly graded), M/C (silty/clayey)
- L/H plasticity division
Relationship to central
Primary classification system used in engineering practice and board exams
AASHTO Classification System
Sub concepts
- Groups A-1 through A-8
- Group index (GI) calculation
- Subgrade quality rating
- Material suitability for highways
- Philippine road design standards
Relationship to central
Highway-focused classification for subgrade evaluation and engineering design
Classification Parameters and Criteria
Sub concepts
- Percent passing #200 sieve
- Percent gravel and sand fractions
- Cᵤ and Cᶜ thresholds for gradation
- LL = 50 boundary for plasticity
- A-line equation: PI = 0.73(LL - 20)
Relationship to central
Quantitative basis for assigning soil types and predicting behavior
Concept connections
- Grain-Size DistributionUniformity Coefficient (Cᵤ)Cᵤ is calculated directly from D₆₀ and D₁₀ extracted from gradation curve
- Uniformity Coefficient (Cᵤ)Well-graded ClassificationCᵤ ≥ 4 (gravel) or ≥ 6 (sand) is first requirement for well-graded soil
- Coefficient of Curvature (Cᶜ)Well-graded ClassificationCᶜ must be between 1 and 3; second requirement completing well-graded criterion
- Atterberg LimitsPlasticity Index (PI)PI = LL - PL; fundamental measure of soil plasticity range
- Plasticity IndexPlasticity ChartPI is y-axis value on chart; defines position relative to A-line for classification
- Liquid Limit (LL)Plasticity ChartLL is x-axis value; LL = 50 defines low vs high plasticity boundary
- A-line EquationSilt vs Clay DistinctionA-line PI = 0.73(LL - 20) separates silt (M, below) from clay (C, above)
- USCS ClassificationCoarse-Grained SoilsUSCS applies G/S designation and modifiers (W/P, M/C) to >50% retained on #200
- USCS ClassificationFine-Grained SoilsUSCS applies M/C/O designation with L/H modifier to ≥50% passing #200
- Percent FinesCoarse-Grained ModifiersFines percentage determines whether modifier is W/P (< 5%) or M/C (≥ 5%)
- AASHTO ClassificationGroup Index (GI)GI formula uses F (% passing #200), LL, and PI to rate subgrade quality
- Group Index ValueSubgrade QualityHigher GI indicates poorer subgrade; GI 0-1 excellent, GI 10+ very poor
- Grain-Size DistributionUSCS ClassificationGrain-size fractions (coarse vs fine) form primary division in USCS system
- Atterberg LimitsUSCS Fine-Grained ClassificationLL and PI determine M/C type and L/H modifier for fine-grained soils
- USCS ClassificationAASHTO ClassificationUSCS grouping provides basis for AASHTO highway subgrade rating
- Effective Size (D₁₀)Permeability PredictionD₁₀ influences soil permeability; smaller D₁₀ indicates lower permeability
- Plasticity Chart PositionEngineering Behavior PredictionClay vs silt classification predicts compressibility and shear strength characteristics
Diagrams
Soil Classification System Hierarchy
Comprehensive mind map showing the hierarchical organization of soil classification concepts, including grain-size distribution parameters, Atterberg limits, USCS categories, and AASHTO grouping system.
USCS Soil Classification Decision Tree
Step-by-step flowchart for USCS soil classification following PRC board exam protocol. Guides from grain-size division through coarse/fine-grained pathways to final soil group designation.
Plasticity Chart Classification Process
Process flowchart for using the plasticity chart to classify fine-grained soils. Shows how LL and PI determine position relative to the A-line and final USCS designation.
AASHTO Group Index Calculation
Step-by-step calculation flowchart for AASHTO group index determination. Includes formula components, constraint applications, and subgrade quality interpretation for highway design applications.
Well-Graded vs Poorly-Graded Soil Assessment
Decision flowchart for determining gradation quality. Emphasizes that BOTH uniformity coefficient and coefficient of curvature must satisfy their respective thresholds for well-graded classification.
Typical USCS Group Distribution in Philippine Projects
Pie chart showing representative distribution of soil types encountered in typical Philippine geotechnical engineering projects. Clayey and silty soils are predominant, reflecting tropical weathering patterns and alluvial deposits common in the Philippines.