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1、Road Design专 业： 交 通 工 程 英文原文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 o

2、f these roads arestill 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）Build on a firm foundation（3）Use the best materials（4）Compact all layers properly（5）Design for traffic

3、 loads and volumes（6）Design 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 e

4、xcess water or to poor waterdrainage. 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 sur

5、face 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

6、 someplace is a problem if it 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 wat

7、er 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 14 higher than the shoulder for each foot o

8、f width from the centerline 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

9、） at the outside of curves will 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 mov

10、e 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 cul

11、verts, 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 t

12、he fall.2 Build on a firm foundationA 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 chemica

13、l 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 materialsWith all road materials you “pay now or

14、pay later.” Inferior materials 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

15、 pavement and traffic by transmitting 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 conditi

16、ons, obtained from established 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 weaken the structur