Environmental Engineering Reference
In-Depth Information
TABLE 7.5
Typical Engineering Properties of Residual Soils of Basalt and Gneiss
Parent Rock
Zone
Location
N
Value (SPT)
LL
PI
e
φ
(deg)
c (
kg/cm
2
) Ref.
a
Granite gneiss
Upper
Georgia
10-25
30-50
9-25
0.7-0.8
(
a
)
Granite gneiss
Intermediate
Georgia
5-10
20-40
0-5
0.8-1.2
Granite gneiss
Saprolite
Georgia
17-70
0.8-0.4
Gneiss
Brazil (coastal
20-70
0-35
1.4-1.0
25-31
0.4-0.6
(
b
)
mountains)
Basalt (porous
Upper
Brazil
35-75
15-40
1.1-1.0
27-31
0.1-0.2
clays)
Gneiss
b,c
Upper
Rio de Janeiro
5-10
(
c
)
Gneiss
b,c
Intermediate
Rio de Janeiro
10-30
20-55
5-25
2.3-0.8
23-43
0-0.4
Gneiss
b,c
Saprolite
Rio de Janeiro
30-50
23-38
0.2-0.5
Gneiss
Upper
São Paulo
8-28
50-70
30-35
(
d
)
Gneiss
Intermediate
São Paulo
7-10
40-50
30-20
Gneiss
Saprolite
São Paulo
10-30
48-50
20-25
Basalt
Upper
Parana, Brazil
53-60
26-18
Basalt
Intermediate
Parana, Brazil
65-45
17-10
24-31
0.1-0.7
a
References: (
a
) Sowers (1954); (
b
) Vargas (1974); (
c
) data courtesy of Tecnosolo S.A.; (
d
) Medina (1970).
b
Strength tests performed at natural moisture; not necessarily saturated.
c
Natural density range: 1.6-1.8 g/cm
3
: saturated, 1.8-2.0 g/cm
3
.
facilitate the entry of water, and decomposition is relatively deep compared with other
rocks. Unweathered quartz veins are typical of gneiss formations.
As shown in
Figure 6.82,
decomposition of gneiss results in two general zones, residual
soils without relict structure (at times referred to as massive saprolite) and saprolite, resid-
ual soils with relict rock structures (see
Figure 6.84).
Typical soil profile zones and engineering characteristics of gneiss are given in
Table 7.6,
and of the boring logs
(
Figure 7.5c and d)
.
A photo of an exposure is given in
Figure 7.3.
Gradation, index test results, and virtual preconsolidation pressure in a boring to a depth
of 10 m in Belo Horizonte, Brazil, are given in
Figure 7.4.
Typical engineering properties
including index and strength values are given in Tables 3.35 and 7.5.
Various Rock Types
Boring logs from four different locations are given in
Figure 7.5.
SPT values and some
index test results for decomposed schist, volcanics, and gneisses are included.
Tropical Residual Soils
Red Tropical or Alteration Soils
Red tropical or alteration soils cover large parts of the world in the middle latitudes
including much of Brazil, the southern third of Africa, Southeast Asia, and parts of India.
They are associated with numerous rock types including basalt, diabase, gneiss, seritic
schist, and phyllite.
Decomposition forms a reddish soil rich in iron, or iron and aluminum, and tropical cli-
mate conditions are required. The degree of laterization is estimated by the
silica-sesquioxide ratio [SiO
2
/(Fe
2
O
3
Al
2
O
3
)] (see
Section 5.3.3)
as follows:
Less than 1.33 — true laterite, a hard rock-like material
●
From 1.33 to 2.0 — lateritic soil
●
Higher than 2.0 — nonlateritic, tropical soil
●
