Physics and Technology – Technology – Roads and Tunnels
Civil engineering includes the construction of roads, tunnels, canals, dams, and bridges. A deciding factor in design is the stability of the geological subsoil in the area.
Roads have to be strong enough to withstand the load of heavy traffic for several decades. Roadways are subjected to compressing and shearing forces, as well as forces exerted by the turbulence of passing traffic.
Additional forces are exerted on a roadway along curves, in high-speed sections, and in sections subjected to the sudden, jolting impact of braking vehicles. In addition to the stress of traffic, forces of nature, such as extreme temperature fluctuations, also trigger damage to roadways.
Structure of roads
Roads are made of a superstructure and a substructure—both of which are designed with a view toward local climatic conditions The superstructure consists of a surface course or top cover to protect the road construction and a lower base course to distribute the load. If required, a protection against frost is also used.
The substructure includes an 8-to-32-inch (20-to-80-cm) underlying layer and an embankment, often consisting of compacted soil. The substructure can extend up to 6.6 feet (two m) below the roadway.
Slope of the road
All roads have a transverse slope to allow surface water to drain off. Where the road curves, this slope is increased to counteract the centrifugal force of the vehicles.
A road’s longitudinal (front-to-back) slope is determined by the structure of the surrounding terrain and must be designed to accommodate the driving speed of vehicles-the faster the traffic on the road, the flatter the road needs to be.
Tunnels
Tunnels provide shorter routes through un- even terrain, but careful geological analysis of the surrounding area is required before their construction. No matter how safe these structures may be, traffic accidents can never be entirely avoided. Sometimes an accident can escalate into a full-blown disaster, such as in the Mont Blanc tunnel in 1999, and at other times in the Tauern and Gotthard tunnels.
Tunnel construction begins by loosening the rock mass with hammers, drills, or dynamite. The loosened rock is then removed with tunnel-boring machines. Modern tunnel construction uses concrete, steel arches, and other construction materials to prevent the collapse of any cleared cavity spaces. In addition, ventilation, water flow, and fire precautions must also be taken into account.
THE GOTTHARD BASE TUNNEL
When it opens in 2015, the Swiss-Italian railway tunnel will he the longest in the world. Its 95-mile (153-km) course was measured out assisted by GPS and laser.
Many factors had to be considered in the structural planning, including varying rock layers, water pressure, and the shifting and growth of the Alps The tunnelinq machines are often up to 1300 feet (400 m) long.
BASICS
ASPHALT is the carefully refined residue from the distillation process of selected crude oils. The primary use of asphalt is in road construction, where it is used as the binder for the
aggregate particles.
WHISPER ASPHALT Whisper asphalt has over 20% air voids and a very smooth riding surface.