Buoyant unit weight (7')

When a soil is below the water table, part of its weight is balanced by the buoyant effect of the water. This upthrust equals the weight of the volume of the water displaced.

Hence, considering unit volume:

Buoyant unit weight = Saturated unit weight — Unit weight of water

-7w 1+e 7w — 7w 1+e Buoyant unit weight is often referred to as submerged unit weight. Density of soil

Similar expressions can be obtained for densities:

Saturated density, psat = pw Dry density, pj = pw

Buoyant density, p' = pw

Relationship between density and unit weight values

In the above expressions, Gs, e, Sr and the number 1 are all dimensionless. Hence a particular unit weight = 7W times a constant. The corresponding density = pw times the same constant.

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