Environmental Engineering Reference
In-Depth Information
V p , m/s
Depth
Zone
Material
A
Humus
Red, brown, or yellow
saturated clay or sand
B
I (Upper)
(mature residual soil)
1 10 m
II (Intermediate)
Red, brown or yellow stiff
to hard clay or clayed sand,
often with quartz veins and mica.
Eventually with relict structure
C
5 15 m
III (Saprolite)
Clay sand mixtures, often
highly micaceous: rock fabric
preserved. Red, brown, white,
grey, eventually containing
boulders or rock strata
moderately decomposed
Boulders or layers of moderately
decomposed rock with soil zones
or layer
5
70 m
IV (Weathered
rock)
5 100 m
V (Slightly
decomposed to
fresh rock)
FIGURE 6.82
Decomposition profile in metamorphic rocks of the coastal mountain range of Brazil. (From Vargas M.,
Proceedings of the 2nd International Congress, International Association of Engineering Geology, Sao Paulo, Vol. 1,
1974. With permission.)
FIGURE 6.83
Moderately decomposed gneiss (Joao
Monevade, Minas Gerais, Brazil).
about 5 to 10% less than that of fresh rock. The material is tough and requires a hammer
to break it, but gives a dull thud, rather than ringing, when struck. In dense rocks the layer
is thin, but in the more porous types it can be many meters thick.
Stage 2 : Saprolite develops; the structure of the parent rock is preserved, but the mass is
altered largely to clay stained with iron oxide. Leaching removes sodium, potassium, cal-
cium, and magnesium; alumina, silica, and iron remain. In Figure 6.84a, the feldspar has
formed white kaolinite and the biotite mica is only partially decomposed; the remaining
minerals are primarily quartz grains. In Figure 6.84b, a sample from a shallower depth, the
minerals remaining are kaolin, iron oxides, and quartz. Saprolites are generally grouped
 
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