Environmental Engineering Reference
In-Depth Information
level benches or terraces high above some river valley. Downcutting by river erosion as
uplift occurs permits the lake bed soils to strengthen as internal drainage results in con-
solidation; as uplift continues and the permanent groundwater table lowers, evaporation
causes prestress by desiccation. The prestress remains even if the lake bed is resubmerged.
Mexico City clays: The famous clays of Mexico City, which extend to depths of 320 ft (70
m), are volcanic materials washed down from the nearby mountains and deposited in
ancient Lake Texcoco. The general geology, the ground subsidence phenomenon, and
foundation problems associated with these clays are described in Section 10.2.4. A log of a
typical test boring is given as Figure 7.60; Values for water contents, unconfined compres-
sive strengths, effective pressures, and specific gravity also are included. As shown in
Effective
pressure
in kg/cm 2
Standard
penetration
blows per foot
Unconfined
compressive
strength in kg/cm 2
Walter content in %
of dry weight of solids
Classification
0.5
10
15
20
25
30
35
50
100 150 200
50
100 150 200
250 300 350 400
0.5
10
15
20
S s
Water table
Piezometric level
Fill
2.55
2.15
2.59
2.07
2.60
2.41
2.36
2.36
2.60
2.20
2.36
2.44
2.39
2.50
2.48
2.51
2.58
2.48
2.48
2.30
2.69
2.44
2.38
2.34
2.50
2.47
2.56
2.44
2.60
2.51
2.40
5
Caliche barriaco
Greenish gray
Silty clay
Brown
10
Olive green
peizometer
Brown
Reddish brown
G ray
Brown
15
Olive green
Brown
Olive green
20
Olive green
Brown
peizometer
Brown
Reddish brown
25
Olive green
peizometer
Olive green
Olive green
30
Gray
Reddish brown
x
Series of deposits
of slit and pine
sand cem with
clay & calcium carb
35
peizometer
B 2
Gray
40
Olive green
2.40
2.26
2.48
2.48
2.38
2.64
2.40
2.54
2.69
2.47
2.50
2.63
White volc. sand
259
A 2
Olive green
45
Gray silty & sandy
peizometer
Series of
deposits of andes
itic gravel, sand
4silt cemented
with clay or
calcium
carbonates
the top of
the deposit
contains very
hard slab-like
concretions
Porous end
517
547
575
50
2.64
55
302
442
330
530
1020
786
60
65
6.5
4.4
2.94
2.30
Brown-root-holes
Olive green
White volc. sand
5.4
2.46
Olive green
70
Gray silty clay with calcium
carbonates root holes and
sand (caliche)
Sand
Water content
Volcanic clay
Sandy silty clay
Unconfined compressive strength
Intergranular effective pressure
including surface load
Atterberg limits
p b = Break in the compressibilty curve
Specific gravity
S s
FIGURE 7.60
Soil section and index properties at the site of the Tower Latino America, Mexico City. (From Zeevaert, L.,
Geotechnique , VII, 1957. With permission.)
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