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Section 5 Applying Technology: Producing Products and Structures
Figure 17-22. This site was finished by
grading the lot and planting landscaping.
lines, highways and streets, waterways,
and airport runways. Other constructed
works help vehicles cross uneven terrain
and rivers. These structures include bridges
and tunnels. Pipelines are land-transpor-
tation structures used to move liquids or
gases over long distances. Let us look at
some examples of these constructed works.
We discuss roadways and bridges.
Roadways
Roads are almost as old as civilization.
People first used trails and paths to travel.
Later, they developed more extensive road
systems. The Romans built the first engi-
neered roads more than 2000 years ago.
Their influence remained until the 1700s,
when modern road building started.
Today’s roads have their roots in the work
of the Scottish engineer John McAdam. He
developed a crushed-stone road built of
three layers of crushed rock, laid in a 10″
(25 cm)–thick ribbon. Later, this roadbed
was covered with an asphalt-gravel mix
that is very common today. A more recent
development is the concrete roadway.
Building a road starts with select-
ing and surveying the route. Next, the
route is cleared of obstacles such as trees,
rocks, and brush. The roadway is graded
so it will drain. Drainage is important to
prevent road damage from freezing and
thawing. Also, a dry roadbed withstands
heavy traffic better than a wet, marshy
one. Another reason for grading is to keep
the road’s slope gentle. Elevation changes
are described using the term grade. Grades
are expressed in percentages. A road with
a 5% grade gains or loses 5′ of height for
every 100′ of distance. Most grades are kept
below 7%.
Once the roadbed is established, the
layers of the road are built. See Figure 17-23.
The graded dirt is compacted, and a layer
of coarse gravel is laid. This is followed
with finer gravel that is leveled and com-
pacted. Next, the concrete or asphalt top
layer is applied. Concrete roads are laid in
produce structures that are sometimes called
civil structures, or heavy engineering structures.
These structures include highways, rail
lines, canals, pipelines, power-transmis-
sion and communication towers, hydroelec-
tric and flood-control dams, and airports.
They provide the paths for the movement of
water, people, goods, information, and elec-
tric power. These projects can be grouped in
various ways. For this discussion, we group
them into transportation, communication,
and production structures.
Transportation Structures
Transportation systems depend on
constructed structures such as railroad
Grading the Lot
Planting Landscaping