Soil Particle Size Distribution: Key Points
Soil particle size distribution is essential for understanding water flow and soil behavior. It measures how the sizes of soil particles are arranged, which affects permeability and strength.
Key Points
- A sieve analysis is used to determine the grain size distribution of coarse-grained soils.
- A hydrometer analysis is used for fine-grained soils to measure their particle size distribution.
- Particle size distribution is represented on a semi-logarithmic plot with percentage finer on the vertical axis and particle size on the horizontal logarithmic scale.
- The plot helps in identifying soil textures by showing the percentages of gravel, sand, silt, and clay.
- The effective size, D10, is the particle diameter at which 10% of the soil is finer, influencing permeability and mechanical behavior.
- D50 represents the average grain size diameter of the soil.
-
Two coefficients characterize the particle size distribution:
- Poorly graded soils have steep gradation curves.
- Well graded soils have flatter curves, indicated by a uniformity coefficient >4 and a coefficient of curvature between 1 and 3.
- Gap-graded soils show humps on the gradation curves, indicating missing particle sizes.
