Environmental Engineering Reference
In-Depth Information
(a)
(b)
(c)
mft
Hard dark gray clay
Brown to grayish
brown silty clay
Topsoil
red-brown,
clayey silt,
thinly bedded
LL = 33
Pl = 10
w
n
= 15
10
30
18
35
LL = 98
Pl = 72
w
n
= 22
(Del rio
shale?)
LL = 38
Pl = 16
w
n
= 24
91
31
100
Buff-colored limestone,
occasional honeycombs
and chert seams
21
10
80%
Limestone fragments
in brown clay
matrix
Brown silty clay
Gray fractured
limestone with
occasional
shale seams
36
5
Void
20
115
Decomposed shale,
(hard clayey silt,
thinly bedded)
Badly fractured limestone
Sound limestone
100/6 in
30
100/4 in
10
Legend:
Column numbers - standard penetration test values
Column %
82%
Fractured shale
- percent core recovery
- groundwater level
- liquid limit (%)
40
Red-brown shale
LL
100%
Pl
- plasticity index
w
n
- natural water content (%)
15
50
FIGURE 7.9
Typical test boring logs from sedimentary rocks. (a) Leesburg, Virgina; (b) Versailes, Kentucky; (c) Round Rock,
Texas. (Courtesy of Joseph S. Ward and Associates.)
In Menlo Park, California, the marine shales are interbedded with sandstones (see
Section 6.7.3).
The shales have weathered to form highly expansive black clays, which
cause differential heaving of foundations and pavements because of the tilted sandstone
interbeds (see
Section 10.6.3).
Limestone
Carbonates, such as limestone and sulfates, pass into solution more quickly than they
decompose, and characteristically thin clayey residual soil results from decomposition and
impurities. The greater the percentage of the impurities, the greater is the thickness of the
soil cover. Transition between the soil and the limestone is normally very abrupt when the
limestone is relatively pure, as shown in
Figures 6.22
and
6.85.
The reddish-brown to red
clays, typical of many limestones in tropical climates, are called “terra rossa.” A log of a test
boring from Versailles, Kentucky, is given in Figure 7.9b, from the location in
Figure 6.22.
7.3
Colluvial Deposits
7.3.1
Introduction
General
Colluvial soils are materials displaced from their original location of formation, normally
by gravitational forces during slope failures.
