Environmental Engineering Reference
In-Depth Information
Schist
(Kensington,
Maryland)
Material
Man-made fill
Yellow-brown
clayey silt and
sand, partings
micaceous
Igneous,
(Humacao,
Puero Rico)
Material
Gneiss,
(Rio de Janeiro,
Brazil)
Material
Gneiss,
(Atlanta,
Georgia)
Materials
e
m t
N
N
N
N
Stiff red micaceous
sandy clay
.72
.76
.80
1.15
1.0
1.1
.85
.90
1.12
1.09
Topsoil
Topsoil
Yellow-brown and gray
clayey silt to
silty clay with
occasional sand
25
25
Orange-brown and
gray mottled sandy
silty clay, trace
fine gravel
Orange-brown and
light gray mottled
gravelly clayey sand
(angular gravel),
occasionally micaceous
12
LL = 30-50
PI = 9-25
15
11
15
27
Soft to firm mica,
fine sandy silt
24
10
LL = 45 to 53
PI = 26 to 34
W
n
= 20 to 29
8
7
9
5
45
5
37
LL = 35
PI = 5
W
n
= 19
47
LL = 20-40
PI = 0.5
5
32
49
Grading to highly
decomposed schist
with depth
(Decomposed
igneous rocks,
lava, breccia,
tuff)
20
LL = 46
PI = 16
W
n
= 35
28
at 2 m
32
38
- Quartz layer
30
.93
.84
60
38
30
Partially decomposed
granite gneiss
10
15
15
35
70
.50
125
37
.42
Light brown to red
sandy clay, trace fine
gravel, saprolite -
rock texture apparent.
Grading to decomposed
granite gneiss.
15
39
40
100/ 3 in. decomposed
schist
27
Legend:
N - SPT (blows/ft)
28
100/1 in
15
36
45
50
- Ground water level
100/4 in
LL - Liquid limit (%)
PI - Plasticity index
W
n
- Natural water content (%)
e
- Void ratio
70
Lava fragments
(a)
(b)
(c)
(d)
FIGURE 7.5
Typical test boring logs from residual soils from igneous and metamorphic rocks. (Parts a-c from Joseph S.
Ward and Associates; Part d from Sowers, G.F.,
Proc. ASCE J. Soil Mech. Found. Eng. Div
., 416, 1954.)
True laterites are hard, forming crusts of gravel and cobble-size fragments on or close to
the surface (see
Figure 7.106)
.
Most of the clay minerals and quartz have been removed, and
iron minerals predominate. Lateritic soils commonly have a surface layer of laterite gravel
as illustrated in
Figure 7.6,
and another layer is frequently found near the limit of saturation.
From the engineering point of view, lateritic soils are not particularly troublesome, since
they consist mainly of kaolin clays and are relatively inactive and nonswelling (CL clays).
In areas where granular quartz materials are lacking, laterite gravels have been used for
aggregate, and large fragments have been used for building-facing stone, since they are
very resistant to weathering.
Tropical Black Clays
Tropical black clays are common in large areas of Africa, India, Australia, and Southeast
Asia. They are associated with mafic igneous rocks such as basalt, in an environment
where rainfall is generally under 90 in. (2250 mm) annually, temperatures are high, and
drainage is poor, resulting in alkaline conditions (Morin and Tudor, 1976). They are not
associated with sialic rocks.
Characteristically black in color, they are composed chiefly of montmorillonite clay and
are highly expansive. Road construction and maintenance are difficult, not only because
of their volume change characteristics, but also because they cover large areas (lava flows)
where there is no granular material for construction aggregate.
7.2.3
Sedimentary Rocks
Sandstones
Composed chiefly of quartz grains, most sandstones develop a profile of limited thickness,
which results from the decomposition of impurities, or unweathered materials, such as
feldspar. The resulting material is low-plasticity clayey sand.
