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1、The Basics of a Good RoadWe 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 arestill in se

2、rvice.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）Build on a firm foundation（3）Use the best materials（4）Compact all layers properly（5）Design for traffic loads and volumes（6）Design

3、for maintenance（7）Pave only when ready（8）Build from the bottom up（9）Protect your investment（10） Keep good records1Get water away from the roadWe cant overemphasize the importance of good drainage.Engineers estimate that at least 90% of a roads problems can be related to excess water or to poor water

4、drainage. Too much water in any layer of a roadsstructure 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 a

5、n 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 i

6、t is not flowingEffective 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

7、. 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 14 higher than the shoulder for each foot of width from the centerline

8、to the edge. For gravel surfaces the crownshould be 12 higher per foot of width. For this flow path to work, the road surface must be 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 w

9、ill also help drainthe 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 drainag

10、e. 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, a

11、nd 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 fo

12、undationA 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 c

13、alled 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 materialsWith all road materials you “pay now or pay later.” Inferior materia

14、ls may require extensive maintenance throughout the roads 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 tra

15、nsmitting the load from particle to particle. By contrast, rounded particles act like ballbearings, 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 establish

16、ed firms, and tested to ensure it meets specifications.4Compact all layersIn 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 weake

17、n 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. Goodcompaction of asphalt pavement lengthens its life.5Design for traffic load

18、s and volumesDesign 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 depa

19、rtment pumper trucks, or construction equipment. If you dont know what specific loads the road will 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 withou

20、t 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 roads life.6 Design for maintenanceWithout maintenance a

21、 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, maint

22、enance and to avoid snow drifts roadsides that are planted or treated to prevent erosion roadsides that can be mowed safelyA 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

23、be located easily.7 Pave only when readyIt 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 pav

24、ing.Dont 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 depending on subgrade soils. A road paved only whe

25、n it is ready will far outperform one that is constructed too quickly.8 Build from the bottom upThis commandment may seem obvious, but it means that you shouldnt 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 surfac

26、e 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 doesnt solve the problem is a waste of money and effort.9 Protect your investmentThe road system ca

27、n be your municipalitys biggest investment. Just as a home needs painting or a new roof, a road must be maintained. Wisconsins severe climate requires more road maintenance than in milder places. Do these important maintenance activities:Surface grade, shape, patch, seal cracks, control dust, remove

28、 snow and iceDrainage clean and repair ditches and culverts; remove all excess materialRoadside cut brush, trim trees and roadside plantings, control erosionTraffic service clean and repair or replace signsDesign roads with adequate ditches so they can be maintained with a motor grader. Clean and gr

29、ade ditches to maintain proper pitch and peak efficiency. After grading, remove all excess material from the shoulder.10 Keep good recordsYour maintenance will be more efficient with good records. Knowing the roads construction, life, and repair history makes it much easier to plan and budget its fu

30、ture 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 cond

31、itions, 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.ResourcesThe Basics of a Good Road #17649,

32、 UW-Madison, 15 min. videotape. Presents the Ten Commandments of a Good Road. Videotapes are loaned free through County Extension offices.Asphalt PASER Manual （39 pp）, Concrete PASER Manual （48 pp）, Gravel PASER Manual （32 pp）. These booklets contain extensive photos and descriptions of road surfacesto help you understand types of distress conditions and their causes. A simple procedure for rating the condition