D 0 + D10

Di (i = 1) =

(3.11)

2

D10 + D 20

Di (i = 2) =

2

D90 + D100

Di (i = 10) =

2

percent, ..., 100 percent of the material (by weight) is finer. Stevens' equation is the

equivalent to utilizing the arithmetic average of the sum of the weights of the individual

particles.

The effective diameter Dm is also used in sediment studies. It is defined by the following

equation:

n

i=1 pi D si

Dm =

(3.12)

100

Where pI is the percentage by weight of that fraction of the sediment with geometric mean

size Dsi. The geometric mean size is the square root of the product of the end points of a

given size range.

Specific weight is weight per unit volume. In the English system of units, specific weight is

usually expressed in units of pounds per cubic foot and in the metric system, in grams per

cubic centimeter. In connection with granular materials such as soils, sediment deposits, or

water sediment mixtures, the specific weight is the weight of solids per unit volume of the

material including its voids. The measurement of the specific weight of sediment deposits is

determined simply by measuring the dry weight of a known volume of the undisturbed

material.

The porosity of granular materials is the ratio of the volume of void space to the total volume

of an undisturbed sample. To determine porosity, the volume of the sample must be

obtained in an undisturbed condition. Next, the volume of solids is determined either by

liquid displacement or indirectly from the weight of the sample and the specific gravity of

material. The void volume is then obtained by subtracting the volume of solids from the total

volume.

3.11

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