Geomechanics 1: Week 3
Coarse grained soil classification
Why do we need to classify soil?
§ To know the particle size distribution
§ Distribution curve is important to assess packing (e.g. well graded, gap graded,
uniformly graded)
§ Type of soil (e.g. sand, clay, gravel)
§ Understanding drainage/permeability characteristics
Clay – low permeability, poor drainage
Sand – high permeability, good drainage
§ Makes selection of soil easy for certain application (e.g. fill, clay core of a dam,
foundation soil)
What parameters do we use to classify soil?
§ Particle Size
- the most significant property
- “Gravel”, “sand”, “silt”, “clay” are common words for particle size.
§ the range of size covers many orders of magnitude.
§ What is the size of human hair -40um
§ What is the minimum size that we can see from a naked eye?
How do we classify soil?
§ We can carry out following two tests:
§ Coarse grained soils (size based)
- Sieve Analysis tests
§ Fine grained soils (size and plasticity)
- Hydrometer test
- Atterberg Limit tests
Sieve analysis in lab - Gravel and sand
§ Sample –oven dried/no lumps
§ Shake it and then determine the mass retained in each sieve
, Grading statistics
D10 = Effective size corresponding to the 10% passing
– 90% of sample is bigger than size D10.
- Cu = D60 / D10 = Uniformity coefficient
Cu = 1 for single size collection
- Cc = (D30 )2/( D10 . D60) = Coefficient of Curvature
D30 = sieve size corresponding to the 30% passing
Coarse grained soil classification
Why do we need to classify soil?
§ To know the particle size distribution
§ Distribution curve is important to assess packing (e.g. well graded, gap graded,
uniformly graded)
§ Type of soil (e.g. sand, clay, gravel)
§ Understanding drainage/permeability characteristics
Clay – low permeability, poor drainage
Sand – high permeability, good drainage
§ Makes selection of soil easy for certain application (e.g. fill, clay core of a dam,
foundation soil)
What parameters do we use to classify soil?
§ Particle Size
- the most significant property
- “Gravel”, “sand”, “silt”, “clay” are common words for particle size.
§ the range of size covers many orders of magnitude.
§ What is the size of human hair -40um
§ What is the minimum size that we can see from a naked eye?
How do we classify soil?
§ We can carry out following two tests:
§ Coarse grained soils (size based)
- Sieve Analysis tests
§ Fine grained soils (size and plasticity)
- Hydrometer test
- Atterberg Limit tests
Sieve analysis in lab - Gravel and sand
§ Sample –oven dried/no lumps
§ Shake it and then determine the mass retained in each sieve
, Grading statistics
D10 = Effective size corresponding to the 10% passing
– 90% of sample is bigger than size D10.
- Cu = D60 / D10 = Uniformity coefficient
Cu = 1 for single size collection
- Cc = (D30 )2/( D10 . D60) = Coefficient of Curvature
D30 = sieve size corresponding to the 30% passing
