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Phase diagram and water content

Soil consists of grains, water and air. In a phase diagram the three parts are drawn on top of each other so masses and volumes are easy to keep track of. The water content is the mass of water divided by the mass of the dry grains.

w=mwmsw = \frac{m_w}{m_s}water content
ρ=mV\rho = \frac{m}{V}density

Symbols

wwwater content%
mwm_wmass of waterg
msm_smass of dry grainsg
Va, Vw, VsV_a,\ V_w,\ V_svolume of air, water and grainsm³

Example

Sample 190 g wet and 160 g dry:

w=30/160≈19 %w = 30/160 \approx 19\,\%.

Water content is relative to dry mass, not wet. That is why it can exceed 100 %.
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Part of Geotechnical Engineering: Soil and classification.