Soil Mechanics / module 4
Particle size, description and classification
Gravel to clay, grading curves and their D-values, and how a soil is described and classified — with its limits.
What you will understand
- Name the particle-size fractions and the coarse/fine division
- Read a grading curve and extract D10, D30 and D60
- Compute the uniformity and curvature coefficients and describe the gradation
- Explain plasticity and how fine soils are classified
- Recognise what classification does and does not tell you
Lessons
Particle sizes and soil description
From boulders to clay platelets — and why the fines change everything.
Grading curves, D-values and coefficients
Read the distribution, then judge whether a soil is well, poorly or gap graded.
Plasticity, classification and its limits
How fine soils are classified, and why classification is only the start.
Module summary
- Soils grade gravel → sand → silt → clay, split into coarse-grained and fine-grained.
- Grading curves give D-values; Cu and Cc describe the spread and shape of coarse soils.
- Fine soils are classified by plasticity; classification captures index properties only.
- Classification is a language and a first filter — measure the design parameters you actually need.
Teaching basis and review status
These are educational models and exercises. Check their assumptions before using the results. The full technical content and every diagram have not yet been independently verified.
Concrete and steel calculations retain their stated first-generation Eurocode teaching basis. Use the standards and amendments specified for your project; do not mix generations without an appropriate design basis.
Read the lesson register and outstanding review notesCheck your understanding
Practice
A well-graded gravel has D10 = 0.5 mm, D30 = 4 mm, D60 = 12 mm. What is Cc?
Check yourself
What does a large uniformity coefficient Cu indicate?