How to use the Soil Phase Relationships Calculator
- 1. Pick what you knowG with e and w, e and Sr, n and w, γ and w, γd and w, or lab masses and volume.
- 2. Enter the valuesSpecific gravity, the two known values and γw (9.81 or 10).
- 3. Get every propertyVoid ratio, porosity, saturation, water content, air content and unit weights.
Key phase relations
The most used identity is Se = wG. From it and the definitions:
- n = e/(1 + e), e = n/(1 − n)
- γ = (G + Se)γw/(1 + e)
- γd = Gγw/(1 + e) = γ/(1 + w)
- γsat = (G + e)γw/(1 + e), γ′ = γsat − γw
- Air content ac = 1 − S, percentage air voids na = n(1 − S)
For lab data: w = (wet mass − dry mass) ÷ dry mass, dry density ρd = dry mass ÷ volume and e = Gρw/ρd − 1.
Worked example and exam tips
A soil has G = 2.7, e = 0.6 and w = 15%. Then S = 0.15 × 2.7/0.6 = 67.5%, n = 0.6/1.6 = 37.5%, γd = 2.7 × 9.81/1.6 = 16.55 kN/m³, γ = 16.55 × 1.15 = 19.04 kN/m³ and γsat = 3.3 × 9.81/1.6 = 20.23 kN/m³.
- Check your answer: S must be between 0 and 100%. If it is more, an input is wrong.
- Some books use γw = 10 kN/m³. Set the same value to match the answer.
- For a fully saturated soil, e = wG.
Frequently asked questions
What is the difference between void ratio and porosity?
Void ratio e is the volume of voids divided by the volume of solids. Porosity n is the volume of voids divided by the total volume. They are related by n = e/(1 + e).
What does Se = wG mean?
Degree of saturation × void ratio = water content × specific gravity. It links the four most used soil properties and solves most phase problems.
Why do I get a saturation above 100%?
The values you entered do not fit together. Check the specific gravity, water content and unit weight. The tool stops with a message instead of showing an impossible answer.
Is this calculator free?
Yes. You fill a short form once to see your result, and other Uncodemy tools then open without the form. Everything is calculated in your browser and nothing you type is uploaded.