ENGINEERING – GEOTECHNICAL ENGINEERING CALCULATOR
Grain Size D50
A precise tool.
What is the Grain Size D50 & How does it work?
Grain‑size analysis is fundamental in geotechnical engineering because it characterises the distribution of particle sizes that control soil behaviour such as permeability, compressibility and shear strength.
The median grain size, denoted D50, is the particle diameter at which 50 % of the soil mass is finer and 50 % is coarser. It is read directly from the gradation curve where the cumulative passing equals 50 %.
A useful index derived from the gradation curve is the coefficient of uniformity (Cu), which quantifies the spread of particle sizes. It is defined as the ratio of the coarse‑grain size D60 to the fine‑grain size D10. A higher Cu indicates a well‑graded soil.
C_{u}=frac{D_{60}}{D_{10}}
Cu = coefficient of uniformity (ratio of D60 to D10)
Parameters
Result
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Frequently Asked Questions
What is the significance of D50 in soil mechanics?
D50, or the median grain size, is a critical parameter that indicates the particle diameter at which half of the soil particles are finer and half are coarser. It influences soil properties like permeability, compressibility, and shear strength.
How do I interpret the D50 value from a gradation curve?
On a gradation curve, D50 is the particle size where the cumulative percentage of soil passing through that size is 50%. It’s found by locating the point on the curve where the line intersects with 50%.
What does a higher D50 value indicate about soil?
A higher D50 value indicates larger particles in the soil, which generally results in lower permeability and compressibility but can affect shear strength depending on other factors.
How is D50 used in practical engineering applications?
D50 is used to assess soil suitability for various construction projects, such as foundations, embankments, and road bases. It helps engineers understand how the soil will behave under different conditions.
Can D50 be calculated from a sieve analysis test?
Yes, D50 can be determined from a sieve analysis by plotting the percentage of material retained on each sieve size and finding the particle size at which 50% of the soil passes through.
What is the relationship between D50 and the coefficient of uniformity?
The coefficient of uniformity (Cu) is related to D50 as it measures the range of grain sizes in a soil sample. Cu is calculated by dividing the diameter of the 60% passing particle size (D60) by the diameter of the 10% passing particle size (D10), and D50 falls between these two values.
How does D50 differ from other grain size parameters?
While D50 represents the median grain size, other parameters like D60 (60% passing) and D10 (10% passing) provide information about the upper and lower limits of the particle size distribution. Together, they help describe the overall gradation of the soil.
Results are for informational purposes only and do not constitute professional advice.