Environmental Engineering Reference
In-Depth Information
TABLE 6.4
Rock Types Characteristic of Intrusive and Extrusive Igneous Bodies
Rock Type
Batholith
Stock
Lapolith
Laccolith
Dike
Sill
Flow
Neck
Pegmatite
X
X
X
X
X
Medium- to coarse-
grained
Granite
X
X
Syenite
X
X
Diorite
X
X
Gabbro
X
X
Peridotite
X
X
X
X
X
X
Pyroxenite
X
X
X
X
X
X
Hornblendite
X
X
X
X
X
X
Dunite
X
X
X
X
X
X
Dolerite
X
X
X
X
X
Fine-grained
Rhyolite
X
X
X
Andesite
X
X
X
Basalt
X
X
X
Felsite
X
X
X
Glass
Obsidian
X
X
X
X
Pitchstone
X
X
X
X
Pumice
X
X
X
X
Scoria
X
X
X
X
Porphyries
X
a
X
a
X
X
X
a
X
a
Contact zones.
These features are extremely significant to engineering works, since they often present
hazardous conditions as discussed in
Section 10.4.
Solution Characteristics
Solution source is rainfall infiltration, especially the slightly acid water of humid climates
penetrating the surface vegetation. This water is effective as a solvent as it moves through
the rock fractures. Its effectiveness increases with temperature and flow velocity.
Cavity growth develops as the rainwater attacks the joints from the surface, causing ero-
sion to proceed downward, creating cavities as shown in
Figure 6.22.
Attack proceeds horizontally at depth to create caverns, as shown in
Figure 6.23,
which
can extend to many meters in diameter and length. The precipitation of calcium carbonate
in the caverns results in the formations of stalactites and stalagmites.
Solution proceeds outward from the cavity, causing it to grow. Eventually, the roof arch
cannot support the overburden load, and it begins to sag to form a dish-shaped area (see
Figure 10.21),
which can be quite large in extent. Finally, collapse occurs and a sinkhole is
formed as illustrated in
Figure 6.24
(see also
Figure 10.15
and
Figure 10.19).
The surface
expression of sinks, as apparent in aerial photos, is given in
Figure 10.20.
The sink illus-
trated in
Figure 6.24
is characteristic of horizontally bedded limestone. Sinkhole develop-
ment in dipping beds of limestone is normally different as discussed in
Section 10.4.2.
Landforms
Landforms developing in limestone are referred to as karst topography. Characteristic fea-
tures vary with climate, the duration of exposure, and the purity of the rock, but in general,
in moist climates, the terrain varies from flat to gently rounded to numerous dome-shaped
