TM 5-818-1/AFM 88-3, Chap. 7
CHAPTER 3
ENGINEERING PROPERTIES OF SOIL AND ROCK
3-1.
Scope.
This chapter considers engineering
Wopt. Table 3-1 presents typical engineering properties
properties of soil and rock useful in designing
of compacted soils; see footnote for compacted effort
foundations under static loading. Dynamic properties are
that applies.
discussed in chapter 17.
a. Correlations. Tables and charts based on
3-3.
Density of cohesionless soils.
a. Relative density of cohesionless soils has a
easily determined index properties are useful for rough
considerable influence on the angle of internal friction,
estimating or confirming design parameters. Testing
allowable bearing capacity, and settlement of footings.
procedures employed by different soil laboratories have
An example of the relationship between relative density
influenced correlations presented to an unknown degree,
and in situ dry densities may be conveniently determined
and the scatter of data is usually substantial; caution
from figure 3-2. Methods for determining in situ densities
should, therefore, be exercised in using correlation
or relative densities of sands in the field are discussed in
values. Undisturbed soil testing, either laboratory or field,
chapter 4.
or both, should be used for final design of major
b. The approximate relationship among the
foundations. On smaller projects, an economic analysis
should determine if a complete soil exploration/laboratory
angle of friction, +, DR, and unit weight is shown in figure
testing program is justified in lieu of a conservative
3-3; and between the coefficient of uniformity, Cu, and
design based on correlation data. Complex subsurface
void ratio, in figure 3-4.
c. The relative compaction of a soil is defined
conditions may not permit a decision on solely economic
grounds.
as
Y field
b. Engineering properties.
Properties of
RC = ------Y--------- x 100(percent) (3-1)
-
max (lab)
particular interest to the foundation engineer include-
(1) Compaction.
where yfield = dry density in field and ymax (lab) = maximum
(2) Permeability.
dry density obtained in the laboratory. For soils where
(3) Consolidation-swell.
100 percent relative density is approximately the same as
(4) Shear strength.
100 percent relative compaction based on CE 55, the
(5) Stress-strain modulus (modulus of
relative compaction and the relative density are related
elasticity) and Poisson's ratio.
by the following empirical equation:
RC = 80 + 0.2DR(DR > 40 percent) (3-2)
3-2.
Compaction characteristics of soils.
The density at which a soil can be placed as fill or backfill
3-4.
Permeability.
a. Darcy's law. The laminar flow of water
depends on the placement water content and the
compaction effort. The Modified Compaction Test (CE
through soils is governed by Darcy's law:
55) or comparable commercial standards will be used as
q = kiA (3-3)
a basis for control. The CE 55 test is described in TM 5-
where
824-2/AFM 88-6, Chapter 2. (See app A for references.)
q = seepage quantity (in any time unit consistent
Other compaction efforts that may be occasionally used
with k)
for special projects include-
k = coefficient of permeability (units of velocity)
a. Standard compaction test: Three layers at
i = h/L = hydraulic gradient or head loss, h,
25 blows per layer Hammer = 5.5 pounds with 12-inch
across the flow path of length, L
drop
A = cross-sectional area of flow
b. Fifteen-blow compaction test:
b. Permeability of soil. The permeability -
Three layers at 15 blows per layer
depends primarily on the size and shape of the soil
Hammer = 5.5 pounds with 12-inch drop
grains, void ratio, shape and arrangement of voids,
The results of the CE 55 test are represented by
degree of saturation, and temperature. Permeability is
compaction curves, as shown in figure 3-1, in which the
determined in the laboratory by measuring the rate of
water content is plotted versus compacted dry density.
flow of wa-
The ordinate of the peak of the curve is the maximum dry
density, and the abscissa is the optimum water content
3-1
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