-
土木工程学院交通工程专业
中英文翻译
Road Design
专
业：
交
通
工
程
英文原文
The Basics
of a Good Road
We have known how to
build good roads for a long time. Archaeologists
have
found ancient Egyptian roadsthat
carried blocks to the pyramids in 4600 BCE.
Later,the Romans built an extensive
road system, using the same principles we use
today. Some of these roads are
still in service.
If you
follow the basic concepts of road building, you
will create a road that will last.
The
ten commandments of a good road are:
（
1
）
Get
water away from the road
（
2<
/p>
）
Build on a firm foundation
（
3
）
Use
the best materials
（
4
）
Compact all layers properly
（
5
）
Design
for traffic loads and volumes
（
< br>6
）
Design for maintenance
（
7
）
Pav
e only when ready
（
8
< br>）
Build from the bottom up
（
9
）
Protect your
investment
（
10
）
Keep good records
1
．
Get water away
from the road
We can’t overemphasize
the importance of good ers estimate that at
least 90% of a road’s
problems can be related to excess water or to poor
waterdrainage.
Too much water in any
laye
r of a road’sstructure can weaken
that layer, leading to failure.
In the surface layer, water can cause
cracks and potholes. In lower layers it
undermines support, causing cracks and
potholes. A common sign of water in an asphalt
road surface is alligator cracking
—
an interconnected pattern
of cracks forming small
irregular
shaped pieces that look like alligator skin. Edge
cracking, frost heaves, and spring
breakup of pavements also point to
moisture problems.
To prevent these
problems remember that water:
? flows
downhill
? needs to flow
someplace
? is a problem if
it is not flowing
Effective
drainage systems divert, drain and dispose of
water. To do this they use
interceptor
ditches and slopes,road crowns, and ditch and
culvert systems.
Divert
—
Interceptor
ditches, located between the road and higher
ground along the
road, keep the water
from reaching the roadway. These ditches must
slope so they carry
water away from the
road.
Drain
—
Creating a crown in the road so it is
higher along the centerline than at the
edges encourages water to flow off the
road. Typically a paved crown should be
1
?
4
th
an the shoulder for each foot of width from the
centerline to the edge. For gravel surfaces
the crown
should be
< br>1
?
2
relatively water tight. Road shoulders also must
be sloped away from the road to continue
carrying the flow away. Superelevations
(banking) at the outside of curves will also help
drain
the road surface.
Dispose
—
A ditch and culvert system carries
water away from the road structure.
Ditches should be at least one foot
lower than the bottom of the gravel road layer
that
drains the roadway. They must be
kept clean and must be sloped to move water into
natural drainage. If water stays in the
ditches it can seep back into the road structure
and
undermine its strength. Ditches
should also be protected from erosion by planting
grass, or
installing rock and other
erosion control measures. Erosion can damage
shoulders and
ditches, clog culverts,
undermine roadbeds, and contaminate nearby streams
and lakes.
Evaluate your ditch and
culvert system twice a year to ensure that it
works. In the fall,
clean out leaves
and branches that can block flow. In spring, check
for and remove silts
from plowing and
any dead plant material left from the fall.
2
．
Build on a firm foundation
A
road is only as good as its foundation. A highway
wears out from the top down but
falls
apart from the bottom. The road base must carry
the entire structure and the traffic
that uses it.
To make a firm
foundation you may need to stabilize the roadbed
with chemical
stabilizers, large stone
called breaker run, or geotextile fabric. When you
run into
conditions where you suspect
that the native soil is unstable, work with an
engineer to
investigate the situation
and design an appropriate solution.
3
．
Use
the best materials
With all road
materials you “pay now or pay later.”
Inferior materials may require
extensive maintenance
throughout the road’s life. They may
also force you to replace the
road prematurely.
Crushed
aggregate is the best material for the base
course. The sharp angles of
thecrushed
material interlock when they are compacted. This
supports the pavement and
traffic by
transmitting the load from particle to particle.
By contrast, rounded particles act
like
ball
bearings, moving under loads.
Angular particles are more stable than
rounded particles.
Asphalt and concrete
pavement materials must be of the highest quality,
designed for
the conditions, obtained
from established firms, and tested to ensure it
meets
specifications.
4
．
Compact all
layers
In general, the more densely a
material is compacted, the stronger it is.
Compaction
also shrinks or eliminates
open spaces (voids) between particles. This means
that less
water can enter the
structure. Water in soil can weaken the structure
or lead to frost
heaves. This is
especially important for unsurfaced (gravel)
roads. Use gravel which has a
mix of
sizes (well-graded aggregate) so smaller particles
can fill the voids between larger
ones.
Good
compaction of asphalt pavement
lengthens its life.
5
．
Design for
traffic loads and volumes
Design for
the highest anticipated load the road will carry.
A road that has been
designed only for
cars will not stand up to trucks. One truck with 9
tons on a single rear
axle does as much
damage to a road as nearly 10,000 cars.
Rural roads may carry log
trucks, milk trucks, fire department pumper
trucks, or
construction equipment.
If you don’t know what specific loads
the road w
ill carry, a good
rule of thumb is to design for the
largest piece of highway maintenance equipment
that will
be used on the road.
A well-constructed and maintained
asphalt road should last 20 years without major
repairs or reconstruction. In designing
a road, use traffic counts that project numbers
and
sizes of vehicles 20 years into the
future. These are only projections, at best, but
they will
allow
you to plan
for traffic loadings through a road’s
life.
6
．
Design for maintenance
Without maintenance a road will rapidly
deteriorate and fail. Design your roads so
they can be easily maintained. This
means:
? adequate ditches that can be
cleaned regularly
? culverts
that are marked for easy locating in the
spring
? enough space for
snow after it is plowed off
the road
? proper cross slopes for safety,
maintenance and to
avoid snow drifts
? roadsi
des that are planted
or treated to prevent erosion
?
roadsides that can be mowed safely
A rule of thumb for adequate road width
is to make it wide enough for a snowplow to pass
another vehicle without leaving the
travelled way.
Mark culverts with a
post so they can be located easily.
7
．
Pave only when ready
It is
not necessary to pave all your roads immediately.
There is nothing wrong with a
well-
built and wellmaintained gravel road if traffic
loads and volume do not require a paved
surface. Three hundred vehicles per day
is the recommended minimum to justify
paving.
Don’t assume that
laying down asphalt will fix a gravel
road that is failing. Before you
pave,
make sure you have an adequate crushed stone base
that drains well and is properly
compacted. The recommended minimum
depth of crushed stone base is
10
subgrade soils. A road paved only
when it is ready will far outperform one that is
constructed too quickly.
8
．? Build from the bottom
up
This commandment may seem
obvious, but it means
that you
shouldn’t top dress or
resurface a road
if the problem is in an underlying layer. Before
you do any road
improvement, locate the
cause of any surface problems. Choose an
improvement technique
that will address
the problem. This may mean recycling or removing
all road materials
down to the native
soil and
rebuilding everything. Doing
any work that doesn’t solve
the
problem is a waste of money and effort.
9
．
?
Protec
t your investment
The
road system can be your municipality’s
biggest
investment. Just as a home
needs
painting or a new roof,
a road must be maintained. Wisconsin’s
severe climate
requires
more
road maintenance than in milder places. Do these
important maintenance activities:
Surface
—
grade, shape, patch, seal cracks,
control dust, remove snow and ice
Drainage
—
clean and repair ditches and culverts;
remove all excess material
Roadside
—
cut brush, trim
trees and roadside plantings, control erosion
Traffic service
—
clean and repair or replace signs
Design roads with adequate ditches so
they can be maintained with a motor grader. Clean
and grade
ditches to maintain proper
pitch and peak efficiency. After grading, remove
all excess material from
the shoulder.
10
．
Keep good records
Your
maintenance will be more efficient with good
records. Knowing the road’s
construction, life, and repair history
makes it much easier to plan and budget its future
repairs. Records can also help you
evaluate the effectiveness of the repair methods
and
materials you used.
Good record keeping starts
with an inventory of the system. It should include
the
history and surface condition of
the roadway, identify and evaluate culverts and
bridges,
note ditch conditions,
shoulders, signs, and such structures as retaining
walls and
guardrails.
Update
your inventory each year or when you repair or
change a road section. A formal
pavement management system can help use
these records and plan and budget road
improvements.
Resources
The Basics of a Good Road
#17649, UW-Madison, 15 min. videotape.
Presents
the Ten Commandments of a Good
Road. Videotapes are loaned free through County
Extension offices.