COMPOSITION OF SOIL
A specimen of moist soil weighing 122 g has an apparent specific gravity of 1.82. The
specific gravity of the solids is 2.53. After the specimen is oven-dried, the weight is 104
g. Compute the void ratio, porosity, moisture content, and degree of saturation of the orig-
inal mass.
Calculation Procedure:
- Compute the weight of moisture, volume of mass, and volume
of each ingredient
In a three-phase soil mass, the voids, or pores, between the solid particles are occupied by
moisture and air. A mass that contains moisture but not air is termed fully saturated; this
constitutes a two-phase system. The term apparent specific gravity (denotes the specific
gravity of the mass.
Let the subscripts s, w, and a refer to the solids, moisture, and air, respectively. Where
a subscript is omitted, the reference is to the
entire mass. Also, let e = void ratio = (Vw +
Va)IV 5 ; n = porosity = (Vw + V 0 )IV; MC =
moisture content = WJW 5 ; S = degree of sat-
uration = VJ(VW + Va).
Refer to Fig. 1. A horizontal line repre-
sents volume, a vertical line represents specif-
ic gravity, and the area of a rectangle repre-
sents the weight of the respective ingredient
in grams.
Computing weight and volume gives W =
122 g; W 3 = 104 g; Ww = 122 - 104 = 18 g;
™-TTt»i7iFIGURE 1. c-1- So A- * F-122/1.82-67.0 cm^3 F 5 =104/2.53 =41.1
1 I ingredients. cm^3 ^ = lg Q ^ 3 ^ = ^ _ (4U + lg Q) =
7.9 cm^3.
- Compute the properties of the original mass
Thus, e = 100(18.0 + 7.9)741.1 = 63.0 percent; n = 100(18.0 + 7.9)767.0 = 38.7 percent;
MC = 100(18)7104 = 17.3 percent; 5= 100(18.0)1(18.0 + 7.9) + 69.5 percent. The factor
of 100 is used to convert to percentage.
Soil composition is important from an environmental standpoint. Ever since the pas-
sage of the Environmental Protection Agency (EPA) Superfund Program by Congress,
greater attention has been paid to soil composition by cities, states, and the federal gov-
ernment.
The major concern of regulators is with soil contaminated by industrial waste and
trash. Liquid wastes can pollute soil and streams. Solid waste can produce noxious odors
in the atmosphere. Some solid wastes are transported to "safe" sites for burning, where
they may pollute the local atmosphere. Superfund money pays for the removal and burn-
ing of solid wastes.
A tax on chemicals provides the money for Superfund operations. Public and civic re-
action to Superfund activities is most positive. Thus, quick removal of leaking drums of
dangerous materials by federal agencies has done much to reduce soil contamination. Fur-
ther, the Superfund Program has alerted industry to the dangers and effects of careless
disposal of undesirable materials.
There are some 1200 dump sites on the Superfund Program agenda requiring
Solids
Moisture
Air
