Figure 5-2.-Conventional graphic soil symbols.
Normally,
the
upper
limit
of
particle
sizes
available
is
controlled
by
the
thickness
of
rock
layers
and
the
spacing
of
cracks
or
fractures
in
the
rock.
The
amount
of
fine
particles
produced
during
rock
crushing
operations
can be highly variable. Generally, hard,
tough rocks produce few fines, and soft,
weak
rocks
produce
large
quantities
of
fines.
Weak
sandstones
and
granites
usually produce large amounts of sand-size
materials.
Types of Quarry Material
Natural sand and gravel are not
always
available,
and
it
is
sometimes
necessary
to
produce
aggregate
by
quarrying and processing rock. Quarrying
normally is performed only where other
materials
of
adequate
quality
and
size
cannot be obtained economically.
Many
rock
types
suitable
for
construction
exist
throughout
the
world;
therefore,
the
quality
and
durability
of
the rock type selected depends on local
conditions. The following rock types are
generally
easy
to
quarry,
durable,
and
resistant to weathering, When these are
not available, it may be necessary to use
softer
rocks
for
base
courses
and
surfacing on a temporary basis. The softer
rocks will usually require little or no
blasting .
Granite.
As
a
dimension
stone,
granite
is
fairly
durable
and
has
a
texture and color desirable for polishing.
As
a
construction
material
for
base
courses
and
aggregate,
it
is
not
as
desirable as some of the more dense, fine-
grained igneous rock.
FelsiteRhyolite.
This
is
durable
and makes a good aggregate for base
courses. It is not suitable for concrete
aggregate.
Gabbro-Diorite.
Gabbro
and
diorite
both have good strength and durability.
The mineral crystals of both rocks are
deeply intermeshed, making them very tough
and
excellent
for
construction
aggregate.
Basalt. The dense variety of basalt,
when crushed, is excellent for use as a
base course. It is very strong and durable.
Sandstone. Few sedimentary rocks are
desirable
for
construction
due
to
their
variable
physical
properties;
however,
sandstone is generally durable. Because of
the variable nature of the types of grains
and cement, each deposit must be evaluated
individually.
5-4