BeginnerTopic 26 of 112Civil & Structural
Soil formation and classification
Soils are classified by grain size and plasticity.
In depth
Soils form by weathering of rock and are transported by water, wind, ice or gravity. Classified by particle size (gravel, sand, silt, clay) and plasticity (USCS, AASHTO). Coarse soils are granular and drain freely; fine soils are cohesive with low permeability.
Key points
- Grain size distribution
- Cu and Cc coefficients
- Organic soils and peat
ExampleClay swells and shrinks with moisture while sand does not.
What is Soil formation and classification?
Soils are classified by grain size and plasticity.
Why is it important to understand soil formation and classification?
Soil classification gives a common language for describing ground, which guides foundation choice and construction methods.
How are soils classified?
By grain size, such as gravel, sand, silt and clay, and by plasticity for fine-grained soils.
What does the particle size distribution tell me?
It shows the proportion of each grain size, which controls drainage, strength and compaction behaviour.
How is Soil formation and classification used in practice?
Typical applications include classifying a site soil as clay or sand before choosing foundations, describing a fill material for a road embankment and choosing a ground treatment based on the soil group.
What should I learn before Soil formation and classification?
Study "Building codes and standards" first (topic 25 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Soil formation and classification?
Grain size distribution. Cu and Cc coefficients. Organic soils and peat.
Can you give an example of Soil formation and classification?
Clay swells and shrinks with moisture while sand does not.
What comes after Soil formation and classification?
The next topic is "Soil phase relationships", which builds directly on this one.
How difficult is Soil formation and classification?
It is classed as Beginner in Civil & Structural (topic 26 of 112). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.