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sma01 - Soils and their Classification Soils What are they...

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Unformatted text preview: Soils and their Classification Soils - What are they? ◆ Particulate materials- Sedimentary origins (usually)- Residual ◆ Wide range of particle sizes- larger particles: quartz, feldspar- very small particles: clay minerals ◆ Voids between particles Aragonite-rich soil x 2000 Need for Simple Classification ◆ Usually soil on site has to be used. – Soils differ from other engineering materials in that one has little control over their properties ◆ Extent and properties of the soil have to be determined ◆ Cheap and simple tests are required to give an indication of engineering properties, e.g. stiffness, strength, for preliminary design The classification must use core samples obtained from the ground. This information is often supplemented by in-situ tests such as cone penetration tests. Classification based on Particle Size ◆ Particle size is used because it is related to mineralogy – e.g. very small particles usually contain clay minerals ◆ Broad Classification – Coarse grained soils » sands, gravels - visible to naked eye Classification based on Particle Size ◆ Particle size is used because it is related to mineralogy – e.g. very small particles usually contain clay minerals ◆ Broad Classification – Coarse grained soils » sands, gravels - visible to naked eye – Fine grained soils » silts, clays, organic soils Procedure for grain size determination ◆ Sieving - used for particles > 75 μ m ◆ Hydrometer test - used for smaller particles – Analysis based on Stoke’s Law, velocity proportional to diameter Procedure for grain size determination ◆ Sieving - used for particles > 75 μ m ◆ Hydrometer test - used for smaller particles – Analysis based on Stoke’s Law, velocity proportional to diameter Procedure for grain size determination ◆ Sieving - used for particles > 75 μ m ◆ Hydrometer test - used for smaller particles – Analysis based on Stoke’s Law, velocity proportional to diameter Grading curves 0.0001 0.001 0.01 0.1 1 10 100 20 40 60 80 100 Particle size (mm) % Finer W Well graded Grading curves 0.0001 0.001 0.01 0.1 1 10 100 20 40 60 80 100 Particle size (mm) % Finer W Well graded U Uniform Grading curves 0.0001 0.001 0.01 0.1 1 10 100 20 40 60 80 100 Particle size (mm) % Finer W Well graded U Uniform P Poorly graded Grading curves 0.0001 0.001 0.01 0.1 1 10 100 20 40 60 80 100 Particle size (mm) % Finer W Well graded U Uniform P Poorly graded C Well graded with some clay Grading curves 0.0001 0.001 0.01 0.1 1 10 100 20 40 60 80 100 Particle size (mm) % Finer W Well graded U Uniform P Poorly graded C Well graded with some clay F Well graded with an excess of fines Simple Classification ◆ In general soils contain a wide range of particle sizes ◆ Some means of describing the characteristics of soils with different proportions of sand/silt/clay is required. Simple Classification ◆ In general soils contain a wide range of particle sizes ◆ Some means of describing the characteristics of soils with...
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sma01 - Soils and their Classification Soils What are they...

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