Classification and identification of soils for general engineering purposes

IS 1498: Scope Summary with Key Tables & Formulas

1. Scope (Clause 3.3.2 & Appendix A)

• Classification of soil components by particle size:

2. Auxiliary Identification (Clause 3.5.1, Table 4)

• Visual & sieve analysis to classify soils as:
  • Highly Organic (Peat)
  • Coarse Grained: ≤ 50% passing 75-micron sieve
  • Fine Grained: > 50% passing 75-micron sieve
• Liquid Limit (LL) classification:
  • Low: LL < 15
  • Medium: 15 ≤ LL ≤ 50
  • High: LL > 50

3. Soil Properties for Pavement Design (Clause 3.8, Table 5)

• Key parameters for subgrade, sub-base, base layers:

IS 1498: Definitions and Basic Soil Components (Clause 3.3.2)

Key Soil Components & Particle Size Ranges (Table 1)

Additional Notes:

• Coarse-grained soils: Characterized by size and compactness (loose/dense), drainage, cementation, and structure.
• Fine-grained soils: Characterized by moisture content, perviousness, structure, cementation, and consistency (soft to hard).
• Foundation soil descriptions should include these parameters for proper engineering assessment (Clause 3.4.10).

Summary Diagram: Soil Particle Size Classification

graph LR
A[Boulder >300mm] --> B[Cobble 300-80mm]
B --> C[Gravel 80-4.75mm]
C --> D[Sand 4.75-0.075mm]
D --> E[Clay <0.075mm]

**Use these definitions and size ranges as a basis for soil classification and

IS 1498: Key Points on Soil Classification and Identification

1. Basic Soil Components (Table 1, Clause 3.3.2)

2. Soil Classification Groups (Table 2, Clause 3.3.3)

3. Classification Criteria for Coarse-Grained Soils (Clause 3.5.1)

• Use grain size distribution (% retained/passed on IS sieves)
• Plasticity index of fines (from Atterberg limits)
• Well graded vs poorly graded based on coefficient of uniformity (Cu) and coefficient of curvature (Cc):

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IS 1498: Coarse-Grained Soils Summary

Definition (Clause 3.1.1)

• Soils with >50% by weight retained on 75-micron IS Sieve.

Particle Size Classification (Table 1, Clause 3.3.2)

Classification Criteria (Clause 3.5.1)

• Use Tables 3 & 4 (not reproduced here) for detailed grading and plasticity limits to classify coarse-grained soils into gravelly or sandy soils with or without fines.

Descriptive Information (Clause 3.4.4)

Record:

• Typical name, max size, % >80 mm
• % gravel, sand, fines (<80 mm)
• Particle shape (angular to rounded)
• Surface coatings, cementation, hardness
• Color, organic content
• Plasticity of fines
• Local/geologic name
• Group symbol

Key Notes:

• Fines: Particles <75 micron; plasticity affects soil behavior.
• Coarse grains are further subdivided by size ranges to assist in classification and engineering judgment.

flowchart LR
    A[Coarse-Grained Soils (>50% >75 micron)] --> B[Boulder >300 mm]
    A --> C[Cobble 80-300 mm]
    A --> D[Gravel 4.75-80 mm]
    A --> E[Sand 75 micron - 4.75

IS 1498: Subdivision of Soils — Key Formulas, Tables & Specifications

1. Basic Soil Components (Table 1, Clause 3.3.2)

2. Soil Classification (Table 2, Clause 3.3.3)

• Coarse-Grained Soils: >50% particles > 75 micron
  • Gravel: GP (clean), GM (with fines), GC (clayey)
  • Sand: SW (clean), SP (poorly graded), SM (silty), SC (clayey)
• Fine-Grained Soils: >50% particles < 75 micron
  • Silts and Clays with varying plasticity: ML, CL, OL (low plasticity), MI, CI, OI (medium), MH, CH, OH (high), Pt (peat)

3. Identification Procedure (Table 4, Clause 3.5.1)

• Visual examination for organic content, grain size distribution by sieve analysis.
• Liquid limit (LL) and Plasticity Index (PI) used to differentiate fines.
• Use plasticity chart zones (A-line) to classify fines.

4. Characteristics for Engineering Use (Table 5, Clause 3.8)

IS 1498: Soil Groups and Symbols Summary

Soil Group Classification (Clause 3.3, Table 2)

Key Notes:

• LL = Liquid Limit (%)
• Plastic fines: Identified by plasticity tests (CL, CI)
• Non-plastic fines: ML, MI groups
• Particles > 80 mm are excluded in field ID.
• Use color codes for mapping (e.g., Red for GP, Yellow for GM/SM, Blue for ML/MH, Brown for OL/OI/OH).

Identification Procedures (Fine Fraction < 425 micron):

• Dry strength: None to high
• Dilatancy:

IS 1498: Field Identification and Classification Procedure (Clause 3.4 & Table 2)

Key Steps:

• Remove particles > 80 mm; classify only particles < 80 mm.
• Determine if soil is coarse-grained (>50% visible particles) or fine-grained (<50% visible particles) by visual estimation.
• Use Table 2 (Classification Chart) starting from left (coarse) to right (fine) to assign Group Symbol.
• Supplement group symbol with detailed descriptive info (grain size, plasticity, moisture, structure, etc.).

Table 2 Summary (Simplified):

Visual Classification Flow (Conceptual):

flowchart TD
    A[Sample < 80mm] --> B{Visible particles > 50%?}
    B -- Yes --> C[Coarse-Grained]
    B -- No --> D[Fine-Grained]
    C --> E{

IS 1498: Laboratory Classification Criteria for Soils

1. Coarse-Grained Soils (Clause 3.5.1, Table 3)

• Classification based on grain size distribution and fines content:

2. Fine-Grained Soils (Clause 3.5.3, Table 4 and Fig.1 Plasticity Chart)

• Plasticity Index (Ip) and Liquid Limit (wL) relationship:

[ I_p = 0.73 (w_L - 20) ]

• Plasticity Chart: Used to classify fine soils into:
  • ML (Silt, low plasticity)
  • CL (Clay, low plasticity)
  • MH (Silt, high compressibility)
  • CH (Clay, high plasticity)
  • OL, OH (Organic silts and clays)
  • Pt (Peat, highly organic)

3. Key Identification Parameters (Clause 3.3.3, Table 2)

• Field and lab description includes:
  • Grain size distribution
  • Plasticity (Ip, wL)
  • Dry strength, dilatancy, toughness (for fines)
  • Organic content (peat, organic clays)
  • Typical color and texture

Summary Diagram: Soil Classification Flow

flowchart TD
    A[Start: Soil Sample] --> B{More than 50% > 75μ

Black Cotton Soils - Key IS 1498 Specifications & Tables

1. Characteristics (Clause 3.6):

• Medium to high compressibility, montmorillonitic clay, black/blackish grey.
• High shrink-swell potential; plasticity chart mostly above 'A' line.
• Care needed for classification near 'A' line.

2. Particle Size (Clause 7.5):

• Coarse: 75 micron to 7.5 micron
• Fine: 7.5 micron to 2 micron

3. Minimum CBR for Design (Note 5, Clause 7.5):

• Minimum CBR = 2% recommended for expansive soils after soaking.

4. Degree of Expansion (Table 8):

5. Suitability for Roads & Foundations (Excerpt from Table 5):

• Black Cotton Soils (CH) have:
  • High compressibility and expansion
  • CBR ≤ 15% (often less)
  • Poor drainage, practically impervious
  • Use sheeps-foot rollers, rubber-tyred rollers for compaction
  • Unit dry weight: 1.44 - 1.84 g/cm³
  • Modulus (k): 1.38 - 4.15 kg/cm²

Summary:

• Black cotton soils are expansive, highly plastic clays with high shrink-swell potential.
• Design with minimum soaked CBR = 2%.
• Expansion severity depends on liquid limit and plasticity indices (see Table

Key Points on Other Inorganic Clays (IS 1498: 3.7, 3.3.2, 3.4.6)

Definition & Classification:

• Other inorganic clays like kaolin behave as inorganic silts.
• They usually lie below the 'A' line on plasticity charts.
• Classified as ML, MI, MH (inorganic silts) despite mineralogical clay nature.

Particle Size & Soil Components (Table 1, Clause 3.3.2)

Identification Tests for Fine-Grained Soils (<425 micron) (Clause 3.4.6)

• Dilatancy Test: Quick water appearance/disappearance indicates silts.
• Dry Strength: Low for silts (easily powdered), medium to high for clays.
• Organic Content & Colour: Dark colour and odour indicate organic content.
• Acid Test: Detects calcium carbonate cementation affecting dry strength.

Classification Symbols for Other Inorganic Clays

Summary Diagram: Soil Particle Size & Classification

graph LR
  A[Coarse-Grained Soils] --> B[Gravel (>4.75 mm)]
  A --> C[Sand (75 micron - 4.75 mm)]
  D[Fine-Grained Soils (<75 micron)] --> E[Clay (C)]
  D --> F[Inorganic Silts (ML, MI, MH

IS 1498: Relative Suitability for General Engineering Purposes

Key Tables & Highlights

Table 5: Soil Characteristics for Roads & Airfields

(Refer to full Table 5 for other soil groups and details.)

Table 7: Suitability for Canal Sections, Compressibility, Workability & Shear Strength

Degree of Expansion of Fine-Grained Soils (IS 1498: Clause 3.9 & Table 8)

Fine-grained soils' expansion depends on clay minerals, Atterberg limits, and free swell.

Key Parameters:

• Liquid Limit (WL)
• Plasticity Index (Ip) = WL - Plastic Limit (PL)
• Shrinkage Limit
• Free Swell (%)

Degree of Expansion Classification (Table 8):

Notes:

• Free swell is the percent increase in volume when soil is submerged in water.
• Soils with free swell > 50% are expansive and critical for design.
• Use Atterberg limits to estimate expansion potential.

Particle Size for Fine and Coarse Grains (Clause 7.5):

• Coarse: 75 μm to 7.5 μm
• Fine: 7.5 μm to 2 μm

Practical Tip:

• For expansive soils, CBR after soaking is often < 2; use a minimum CBR of 2 for pavement design (Note 5, Table 5).

flowchart TD
    A[Fine-Grained Soil] --> B{Liquid Limit (WL)}
    B -->|20-35| C[Low Expansion]
    B -->|35-50| D[Medium Expansion]
    B -->|50-70| E[High Expansion]
    B -->|70-90

IS 1498: Manual Identification Tests for Fine-Grained Soils (<425 micron fraction)

Key Tests (Clause 3.4.6):

1. Dilatancy Test (Reaction to Shaking)

   • Soil pat (~5 cm³) nearly saturated.
   • Shake horizontally, strike against palm.
   • Observe water appearance/disappearance:
     • Quick reaction: Water appears/disappears rapidly.
     • Slow reaction: Water appears/disappears slowly.
     • No reaction: No visible water change.
   • Used as descriptive info on soil behavior.

2. Dry Strength Test (Crushing Resistance)

   • Dry soil pat and attempt to powder it between fingers.
   • Classification:
     • Low: Easily powdered.
     • Medium: Requires pressure.
     • High: Cannot be powdered.
   • Indicates plasticity and colloidal content.
   • High dry strength may indicate cementing agents (CaCO₃, Fe oxides).
   • Confirm with acid test for calcium carbonate.

3. Organic Content and Colour

   • Fresh organic soils: distinct decomposed odour, dark colour.
   • Tropical dark soils may be organic or due to poor drainage.
   • Dry organic clays emit earthy odour when moistened.

4. Acid Test

   • Apply dilute HCl to detect calcium carbonate.
   • Strong effervescence indicates CaCO₃ cementing agent.

5. Miscellaneous Tests

   • Feel test: Clay sticks and dries slowly; silt dries quickly and leaves stain.
   • Experience-based identification supported by lab tests.

Summary Table: Soil Reaction & Identification

IS 1498: Suitability & Engineering Properties of Soil Groups

1. Soil Group Classification (Clause 3.3, Table 2)

• Coarse-Grained Soils (more than 50% > 75μm):
  • Gravels: GP (clean), GM (with fines), GC (clayey)
  • Sands: SW (clean), SP (poorly graded), SM (silty), SC (clayey)
• Fine-Grained Soils (more than 50% < 75μm):
  • Silts & Clays with low plasticity: ML, CL, OL
  • Medium plasticity: MI, OI
  • High plasticity: MH, CH, OH
  • Highly organic: Pt (peat)

2. Key Tables for Engineering Suitability (Clauses 3.8, Tables 5-7)

• Table 5: Soil suitability for roads & airfields (strength, drainage, frost susceptibility)
• Table 6: Suitability for embankments & foundations (bearing capacity, compressibility)
• Table 7: Suitability for canals, compressibility, workability, shear strength

3. Important Parameters & Guidelines

• Plasticity Index (PI) & Liquid Limit (LL): Classify fine soils for compressibility and shear strength.
• Relative Suitability: Soils with low fines and good gradation (e.g., GP, SW) are preferred for foundations and embankments.
• Compressibility: High in CH, OH, Pt groups; unsuitable without treatment.
• Workability: Clean sands/gravel easier; organic soils difficult.
• Shear Strength: Higher in coarse-grained, lower in high plasticity clays.

Summary Table: Soil Group vs Key Properties

Key Specifications & Tables for Description of Foundation Soils (IS 1498: Clause 3.4.10 & 3.3.2)

1. Description Requirements

2. Basic Soil Components (Table 1, Clause 3.3.2)

3. Notes on Soil Classification

• Consistency and compactness must be described from *und