Handbook of Civil Engineering Calculations

2. State the equation relating the four defined quantities
   Thus,

H(e{ - e 2 )

'-TT^

(31)

3. Solve for e 2
   Thus: H= 30 in (762.0 mm); s = 0.50 in (12.7 mm); C 1 = 0.960; e 2 = 92.7 percent.

COMPRESSION INDEX AND VOID RATIO

OFA SOIL

A soil specimen under a pressure of 1200 lb/ft^2 (57.46 kPa) is found to have a void ratio
of 103 percent. If the compression index is 0.178, what will be the void ratio when the
pressure is increased to 5000 lb/ft^2 (239.40 kPa)?

Calculation Procedure:

1. Define the compression index
   By testing a soil specimen in a consolidometer, it is possible to determine the void ratio
   associated with a given compressive stress. When the sets of values thus obtained are
   plotted on semilogarithmic scales (void ratio vs. logarithm of stress), the resulting dia-
   gram is curved initially but becomes virtually a straight line beyond a specific point. The
   slope of this line is termed the compression index.


2. Compute the soil void ratio
   Let Cc = compression index; ^ 1 and e 2 — original and final void ratio, respectively; Cr 1 and
   (T 2 - original and final normal stress, respectively.
   Write the equation of the straight-line portion of the diagram:

^ 1 -S 2 = QlOg- (32)

(T 2

Substituting and solving give 1.03 - e 2 = 0.178 log (5000/1200); e 2 = 92.0 percent. Note
that the logarithm is taken to the base 10.
Landfills—where municipal and industrial wastes are discarded—are subject to soil
consolidation because of gradual contraction of the components. To hasten this contrac-
tion and reduce the space needed for trash, some communities are mining established
landfills.
When a trash landfill is mined, more than half of the contents may be combustible in
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obtain useful power from the mined trash while reducing the volume of the trash by 75
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required.
Mining of landfills also saves closing costs, which can run into millions of dollars for
even the smallest landfill. Current EPA regulations require a landfill to be monitored for