12/05/2026
Soil Types & Particle Size Classification β As per IS Codes & IRC Guidelines ποΈ
Understanding soil classification is one of the most important fundamentals in civil engineering. The strength, stability, drainage, and performance of every structure depend on the type of soil beneath it.
# # # π Standard References:
* **IS 1498:1970**
* **IS 2720 (Part 4)**
* **IRC SP:72-2015**
# # # π Major Soil Classifications Based on Particle Size
# # # # πͺ¨ Coarse Grained Soils
**(More than 50% retained on 75 micron sieve)**
βοΈ **Boulders** β > 300 mm
βοΈ **Cobbles** β 75 β 300 mm
βοΈ **Gravel (Coarse)** β 20 β 75 mm
βοΈ **Gravel (Fine)** β 4.75 β 20 mm
βοΈ **Sand (Coarse)** β 2.0 β 4.75 mm
βοΈ **Sand (Medium)** β 0.425 β 2.0 mm
βοΈ **Sand (Fine)** β 0.075 β 0.425 mm
π«οΈ Fine Grained Soils
(More than 50% passing 75 micron sieve)**
βοΈ **Silt** β 0.075 β 0.002 mm
βοΈ **Clay** β < 0.002 mm
π± Organic Soils
βοΈ Contains organic matter, peat, decomposed vegetation, etc.
βοΈ Generally weak for foundation support
π Why Soil Classification Matters?
β
**Foundation Design**
β
**Pavement & Highway Construction**
β
Earthwork & Embankment Design
β
Drainage & Permeability Analysis
β
Settlement & Stability Evaluation
β
Selection of Construction Methods
π§ Engineering Importance of Different Soils
πͺ¨ Gravel β Excellent drainage & load bearing
ποΈ Sand β Good compaction and stability
π«οΈ Silt β Poor drainage and moderate strength
π§± Clay β High plasticity and shrink-swell behavior
π± Organic Soil β Highly compressible and weak
π Common IRC / IS Soil Groups
βοΈ GW β Well Graded Gravel
βοΈ GP β Poorly Graded Gravel
βοΈ SW β Well Graded Sand
βοΈ SP β Poorly Graded Sand
βοΈ CL β Lean Clay
βοΈ CH β Fat Clay
βοΈ ML β Silt
βοΈ OL / OH β Organic Soil
A proper understanding of soil classification helps engineers build safer, stronger, and more durable infrastructure. ππ·ββοΈ