What the curve represents
A particle size distribution curve shows the relationship between particle size and the percentage of a soil sample that is finer than that size. It is used to describe the distribution of particle sizes in a soil sample.
Axes
- The horizontal axis commonly represents particle or sieve opening size on a logarithmic scale.
- The vertical axis represents percent finer, also called percent passing, on a linear percentage scale.
Plotting workflow
- Arrange sieve opening values from large to small or in the required plotting order.
- Calculate the percentage finer for each sieve from the recorded masses and the retained/cumulative retained values.
- Place each point using the logarithmic x-axis and linear y-axis.
- Connect the points smoothly according to the plotting convention used by the laboratory manual.
Reading the curve
The curve can be used to estimate characteristic particle sizes such as D10, D30 and D60 when the plotted data span those percentages. These values are read from the curve at the corresponding percent-finer levels; the calculation method and any soil classification should follow the course or standard being used.
Check that sieve opening units are consistent before plotting. A logarithmic x-axis is not interchangeable with an ordinary linear axis.