CELE Geotechnical Engineering — Soil ClassificationConcept Map

Concept

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

Concept

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

Concept

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

Concept

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

Concept

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

To

Uniformity Coefficient (Cᵤ)

From

Grain-Size Distribution

Strength

strong

Relationship

Cᵤ is calculated directly from D₆₀ and D₁₀ extracted from gradation curve

To

Well-graded Classification

From

Uniformity Coefficient (Cᵤ)

Strength

strong

Relationship

Cᵤ ≥ 4 (gravel) or ≥ 6 (sand) is first requirement for well-graded soil

To

Well-graded Classification

From

Coefficient of Curvature (Cᶜ)

Strength

strong

Relationship

Cᶜ must be between 1 and 3; second requirement completing well-graded criterion

To

Plasticity Index (PI)

From

Atterberg Limits

Strength

strong

Relationship

PI = LL - PL; fundamental measure of soil plasticity range

To

Plasticity Chart

From

Plasticity Index

Strength

strong

Relationship

PI is y-axis value on chart; defines position relative to A-line for classification

To

Plasticity Chart

From

Liquid Limit (LL)

Strength

strong

Relationship

LL is x-axis value; LL = 50 defines low vs high plasticity boundary

To

Silt vs Clay Distinction

From

A-line Equation

Strength

strong

Relationship

A-line PI = 0.73(LL - 20) separates silt (M, below) from clay (C, above)

To

Coarse-Grained Soils

From

USCS Classification

Strength

strong

Relationship

USCS applies G/S designation and modifiers (W/P, M/C) to >50% retained on #200

To

Fine-Grained Soils

From

USCS Classification

Strength

strong

Relationship

USCS applies M/C/O designation with L/H modifier to ≥50% passing #200

To

Coarse-Grained Modifiers

From

Percent Fines

Strength

moderate

Relationship

Fines percentage determines whether modifier is W/P (< 5%) or M/C (≥ 5%)

To

Group Index (GI)

From

AASHTO Classification

Strength

strong

Relationship

GI formula uses F (% passing #200), LL, and PI to rate subgrade quality

To

Subgrade Quality

From

Group Index Value

Strength

strong

Relationship

Higher GI indicates poorer subgrade; GI 0-1 excellent, GI 10+ very poor

To

USCS Classification

From

Grain-Size Distribution

Strength

strong

Relationship

Grain-size fractions (coarse vs fine) form primary division in USCS system

To

USCS Fine-Grained Classification

From

Atterberg Limits

Strength

strong

Relationship

LL and PI determine M/C type and L/H modifier for fine-grained soils

To

AASHTO Classification

From

USCS Classification

Strength

moderate

Relationship

USCS grouping provides basis for AASHTO highway subgrade rating

To

Permeability Prediction

From

Effective Size (D₁₀)

Strength

moderate

Relationship

D₁₀ influences soil permeability; smaller D₁₀ indicates lower permeability

To

Engineering Behavior Prediction

From

Plasticity Chart Position

Strength

moderate

Relationship

Clay vs silt classification predicts compressibility and shear strength characteristics