George P. Coleman Bridge

Brief information:

Location: Yorktown, Virginia, USA

Completion Date: 1952 (original), 1995 (reconstruction)

Cost: $9 million (original), $76.8 million (reconstruction)

Length: 3,750 feet

Type: Movable (double swing span)

Purpose: Highway

Materials: Steel, concrete

Longest Single Span: 500 feet

Engineer(s): Parsons Brinckerhoff, Inc.

In the spring of 1995, the largest double-swing-span bridge in the United States was dismantled and replaced in only nine days. The George P. Coleman Bridge in Virginia was originally constructed in 1952 as a two-lane highway designed to carry no more than 15,000 vehicles a day. By 1995, the population around the bridge had increased so much that the structure was carrying in excess of 27,000 vehicles a day.

To make matters worse, the machinery that rotated the massive swing spans often experienced mechanical problems. In short, the bridge was a major headache. Engineers considered several designs to ease congestion -- from building a tunnel to constructing a new bridge upstream -- but the least expensive option proved to be reconstruction of the existing bridge. So between May 4 and May 13, 1995, about 2,500 feet of truss and swing spans -- complete with pavement, lightpoles, and barrier walls -- were floated in six sections over 40 miles from Norfolk, Virginia, to the bridge site. It marked the first time in engineering history that such an enormous bridge was assembled off site and floated into place.

The new four-lane bridge is three times wider than the original bridge and can now carry up to 50,000 vehicles daily.

Fast Facts:

· The George P. Coleman Bridge is the largest double-swing-span bridge in the United States and the second largest in the world.

· The new bridge weighs only 25 percent more than the original because the new spans are made of lightweight, high-strength steel.

· The two main river piers contain mechanisms that lift the swing spans to different elevations so they don’t hit each other when they rotate.

Chesapeake Bay Bridge-Tunnel

Lead-in

Look at the picture and answer the following questions

1. Why is the bridge-tunnel considered unique?

2. What do you think about the length of the complex?

3. What is the main purpose of the bridge-tunnel complex?

Brief information:

Location: Cape Charles and Virginia Beach, Virginia, USA

Completion Date: 1964

Cost: $200 million

Length: 89,760 feet (total length); 79,200 feet (bridge length)

Type: Beam, tunnel

Purpose: Roadway

Materials: Steel, concrete

Longest Single Span: 100 feet

Engineer(s): Sverdrup & Parcel

Distinguished as an "Outstanding Civil Engineering Achievement" by the American Society of Civil Engineers in 1965, the Chesapeake Bay Bridge-Tunnel is nothing short of a modern engineering wonder. Dipping over and under open waters with a complex chain of artificial islands, tunnels, and bridges, the Chesapeake Bay Bridge provides a direct link between Southeastern Virginia and the Delmarva Peninsula.

The bridge-tunnel complex is 17.6 miles long from shore to shore, and it cuts 95 miles off the journey between Virginia Beach and points north of Wilmington, Delaware. The majority of the bridge-tunnel complex is above the water, supported by more than 5,000 piers. But due to the importance of shipping in the bay, the crossing was sunk deep beneath the bay in two mile-long tunnels to allow the passage of ships. Four artificial islands, each with approximately 10 acres of surface, provide the portals by which the road enters the tunnels. The original Chesapeake Bay Bridge-Tunnel 2-lane crossing consists of 12.5 miles of low level concrete bridge trestles, two tunnels each about one mile long, two high-level steel bridges, four man-made portal islands each 1,500 feet long, 1.5 miles of earthfill causeway across Fisherman Island, and about 5.5 miles of land approach highway. The roadway on the bridge portions is 28 feet wide.

The individual components of the Bridge-Tunnel are not the longest or the largest ever built; however, the total project is unique in the number of different types of major structures included in one crossing and the fact that construction was accomplished under the severe conditions imposed by northeasters, hurricanes, and the unpredictable Atlantic Ocean. It's quite an eerie experience to be driving along and see the road you're on disappear into the bay. Since it opened (1965), more than 67 million vehicles have crossed the Chesapeake Bay Bridge-Tunnel. It's possible that many just crossed it for the thrill of it! It is mandatory that the bridge be checked and serviced every five years. Since servicing the bridge takes about five years, the work never stops.

Fast Facts:

· Following its opening in 1964, the Bridge-Tunnel was selected as "One of the Seven Engineering Wonders of the Modern World" in a worldwide competition that included more than 100 major projects.

· Since it opened in 1965, more than 67 million vehicles have crossed the Chesapeake Bay Bridge-Tunnel.

· One artificial island actually has a gift shop, restrooms, and a parking lot to allow drivers to stretch, relax, and enjoy the scenic view.

· Four artificial islands, each with approximately 10 acres of surface, provide the portals by which the road enters the tunnels.

Text 1. TUNNEL

Tunnel is an underground passageway. The definition of what constitutes a tunnel is not universally agreed upon. However, in general tunnels have a ratio of the length of the passage to the width of at least 2 to 1. In addition, they should be completely enclosed on all sides (save the openings) for the length of the covered area. Tunnels were known in ancient times. They were, for instance, driven into the rock under the Pyramids of Egypt, and the Romans built one in Rome for their chief drain, parts of which still remain. One of the earliest tunnels known was made in Babylon. It passed under the Euphrates river and was built of arched brickwork being 12 feet high and 15 feet wide. Other ancient tunnels were built for water supply and for drainage. Tunnels are dug through hills and mountains, and under cities and waterways. They provide highways, subways, and railroads with convenient routes past natural and artificial obstacles. Miners use tunnels to reach valuable minerals deep within the earth. Tunnels also carry large volumes of water for hydroelectric power plants. Some tunnels provide fresh water for irrigation or drinking, and oth­ers transport wastes in sewer systems. In addition, tun­nels provide underground space for cold storage. A tunnel may be for pedestrians and/or cyclists, for general road traffic, for motor vehicles only, for rail traffic, or for a canal. while others carry other services such as telecommunications cables. There are even tunnels designed as wildlife crossings for European badgers and other endangered species. Some secret tunnels have also been made as a method of entrance or escape from an area. In the UK a pedestrian tunnel or other underpass beneath a road is called a subway. This term was also used in the past in the US, but is now used to refer to underground rapid transit systems. The central part of a rapid transit network is usually built in tunnels. To allow non-level crossings, some lines are in deeper tunnels than others. At metro stations there are usually also pedestrian tunnels from one platform to another. Often, ground-level railway stations also have one or more pedestrian tunnels under the railway to enable passengers to reach the platforms without having to walk across the tracks.

For water crossings, a tunnel is generally more costly to construct than a bridge. However, navigational considerations may limit the use of high bridges or drawbridge spans when intersecting with shipping channels at some locations, necessitating use of a tunnel. Additionally, bridges usually require a larger footprint on each shore than tunnels; in areas with particularly expensive real estate, such as Manhattan and urban Hong Kong, this is a strong factor in tunnels' favor. Examples of water-crossing tunnels built instead of bridges include the Holland Tunnel and Lincoln Tunnel between New Jersey and Manhattan in New York City, and the Elizabeth River tunnels between Norfolk and Portsmouth, Virginia and the Westerscheldetunnel, Zeeland, Netherlands. Some water crossings are a mixture of bridges and tunnels, such as the Denmark to Sweden link.