Reading 2

Unit 1- Reading 2

Page 8

Understanding Philly’s Basement

Philadelphia, a large city on the east coast of the United States, is one of the oldest and most important cities in the country. People walking through the city assume they are standing on a rock-solid place. In reality, just below the surface is a vast, dark, and complex environment—water pipes, sewers, electrical wires, and television cables. There are also tunnels, abandoned subway stations, graves, hidden waterways, archaeological sites, mines, and more. Sometimes, one of these underground structures fails. A small break in a pipe can eventually create a sinkhole that swallows is whatever stood above it. One June day, in a location not far from Philly, two cars fell 70 feet when an enormous sinkhole opened up in a busy highway, that same day, two truckers were filled after their rigs fell into a sinkhole on Interstate 99 in New York State, to the north of Pennsylvania.

AN UNDERGROUND MYSTERY

So just how bad things down there in are lower Philadelphia? The answer is simple and frightening: We don’t know. Philadelphia was carefully planned out by William Penn, who established the city in 1682.

The well-organized Mr. Penn obviously had little influence below the surface. The city’s underground has been built, liberally expanded, and repaired in no particular order for more than 300 years. Some underground work was never documented. For example, in the mid-1800s, anti-slavery groups hid escaped slaves in secret shelters below ground to keep them from being kidnapped and returned to the South. In the past, various ethnic groups in the city were sometimes fearful or suspicious of city authorities. They built underground meeting rooms, storehouses, and even treasure vaults for their communities.

Even if records were kept, they may be of no help. Many have been scattered or lost, or were simply inaccurate to begin with. This matters for many reasons. The most important is that new systems are hard to plan unless you know where the old ones are. And then there are sinkholes. Until we figure out exactly what is where, we cannot predict where the next man-eating hole might develop.

MAPPING THE DEPTHS

“Philadelphia is an old city,” says Lucio Soibelman, an associate professor of civil and environmental engineering at Carnegie Mellon University, “so you have old infrastructure’ and new infrastructure. You have new pipes that are being mapped with GIS (geographic information systems) technology and you have old things that no one knows are there. This is not something that was designed in a perfect way.

There’s a lot going on, and a lot of research is needed to find out what is underground.” The most common technique for finding buried pipes or cables is to use a kind of metal detector. The problem is that many underground utilities aren’t metal. Many gas pipes are plastic. The channels of the sewer system are lined with baked clay or plastic.

To make it easier for people to find them again, most glass fiber optic cables and many newer nonmetallic pipes contain “tracer wires” that can be picked up by metal detectors. Older pipes, however, remain invisible. Ground penetrating radar (GPR) is an important new tool. In a way, it is similar to the sonar systems used to locate objects under water. GPR sends thousands of radar pulses per second into the ground. The signals are then either absorbed or reflected back to a receiver. Software senses how long it takes the GPR signals to bounce back. Differences of even a nanosecond in bounce-back time will be registered. A software-generated image of what lies beneath the surface soon emerges on the receiver’s screen.

An underground mystery unique to Philadelphia was finally unraveled in 2005 by using GPR. An escape tunnel under Eastern State Penitentiary (a prison) in the Fairmount neighborhood was used in 1945 by a group of twelve prisoners. Their clever tunneling work.

Notwithstanding, they were all easily recaptured in the city. Their muddy footprints showed exactly where they were hiding. Authorities knew where the tunnel started, but they didn’t know until the 2005 GPR readings exactly where it went. The detection of other abandoned tunnels is important to law-enforcement authorities. Such underground passageways could be used by persons trying to immigrate illegally through Philly’s seaport. Smugglers’ or other criminals could also find them useful. The police want to know where they are, and GPR is a big help.

Robots that can patrol large water systems are another great innovation. They are already used in other cities. In Pittsburgh, for example, a robotic system called Responder travels inside sewers, operated by a remote control, looking for problems in the pipes. Responder is equipped with laser and sonar sensors that scan the insides of pipe walls. The slightest bit of corrosion’ or the smallest leak will register. Advanced software can then construct extremely detailed 3-D models of the pipe walls.

OK. NOW WHAT?

Locating problems is important, but it’s not enough. Fixing them is the bulk of the jcib. Fixing and updating underground utilities in a city is very complicated. It’s not just a matter of digging a hole, pulling out bad pipes, and installing good ones. The city and its neighborhoods must Continue functioning during the many months it takes to put things right.

A company named Insituform has developed technology that can fix a pipe from the inside before it breaks, without any digging. Workers fill a tube with a special kind of resin a sticky substance) and send it through the pipe. Then they heat the water inside the pipe. The resin expands outward, attaches to the interior surface of the pipe, and then hardens.

This creates a new pipe inside the old pipe. The company actually used this technique on the sewers under one of the most famous buildings in the United States, the White House, in Washington, D.C. The pipes dated from the mid-1800s and needed extensive repair. For security reasons—and because it would look really ugly—the government decided not to dig up the lawn, but rather to work underground, two and under tourists’ feet.