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MAY 24, 2004
Saving a Colonial Past from Sinking Spanish-era structures that have managed to survive so far on Mexico City's former lakebed are getting high-tech lifesaving help Mexico City's historic downtown area used to be the heart and soul of the metropolis, full of university students, lawyers, bookstores, and cafés. It was also the center of commerce, much like New York's Garment District, Lower East Side, and Soho all thrown together. Need to find a blue feather boa for an evening costume? Go downtown. Need replacement parts for a 30-year-old water pump? Head downtown. You can still buy almost anything under the sun near the Zócalo, the huge downtown plaza where the ancient Aztecs had their open-air markets. Today's street vendors hawk pirated DVD movies and contraband toys and clothing from China. You won't find many university students and their bohemian haunts in the city center today, though: The huge national university was moved to the south of the city in the 1950s. The neighborhood went downhill, and it never really recovered from the devastating 1985 earthquake that killed thousands in the collapse of hundreds of buildings constructed on the cheap in the 1940s and 1950s, including apartment blocks and a city hospital. That's because most of downtown Mexico City was constructed on the clay bottom of the old Lake Texcoco, drained by Spanish engineers in the 1600s and 1700s. When earthquakes hit, the ground shifts freely. Buildings with inadequate foundations bit the dust, while colonial structures have survived intact. TECTONIC SHIFTS. For the past few years, however, Mexico's historic downtown, which was first occupied seven centuries ago by the Aztecs, has been undergoing a metamorphosis. Colonial buildings are being restored, streets are being repaved and plazas beautified, and security is improving as police patrols are stepped up and dozens of video cameras are installed in the area. At the same time, engineers are working to ensure that the downtown area's oldest colonial buildings survive another few centuries. "This is one of the only places in the world where pre-Hispanic, Hispanic colonial, and today's world intermingle, right in front of your eyes," says Mexican historian Guillermo Tovar y de Teresa. "As an historic center, it's definitely the most important in Latin America and perhaps one of the world's most important. It's important to preserve it." As you walk through the downtown area, you'll see hundreds of stone palaces and churches built by the Spaniards that have survived centuries of floods, tectonic shifts, and subsoil erosion. Some are sunk several feet below street level, and others are tilted noticeably to one side. That's because the ground downtown is sinking at a rate of 2½ inches per year -- some 27 feet in the last century or so. LEFTWARD LEAN. Enrique Santoyo, a construction engineer who's an expert on shoring up the foundations of the city's historic structures, says some of the older buildings took years, often decades, to construct. That gave their heavy stone foundations time to settle into the porous clay ground. If architects found the buildings they were erecting were sinking at an angle, they would simply make the supporting columns on one side longer than on the other. If you stand in front of the massive Metropolitan Cathedral, whose construction began in 1573 and took 240 years to complete, you'll notice that its main tower tilts noticeably to the left, while an adjacent chapel tilts to the right. The lean used to be more pronounced. Santoyo was part of a Mexican team that rescued the huge cathedral from eventual collapse by embarking on a six-year, $33 million project to shore it up. The cathedral, which weighs 161,000 tons and rests on 22,500 wood pilings, was built atop irregular thicknesses of soft clay, plus the remains of 11 Aztec pyramids. Some corners of the building were sinking into the clay faster than the center was. The cathedral's main tower was tilting so much -- 2.7 degrees out of plumb, in engineering terms -- that a large earthquake could cause it to collapse. REMOVING RISK. The team of engineers, who frequently compared notes with Italian colleagues who stabilized the Tower of Pisa, devised a method for reducing the tilt and minimizing future uneven sinking: First, they erected scaffolding throughout the cathedral to prevent its collapse during the operation. Then, they went underneath it, into the foundation, and drilled 32 vertical shafts as deep as 60 feet each, removing 150,000 cubic feet of clay from areas where they wanted higher sections of the building to settle in next to sunken sections. They were able to reduce the inclination of the cathedral's main tower by one-third (it's now just 2 degrees out of plumb). Then, in a real feat of ingenuity they reduced the likelihood of future settling by "hardening" the subsoil: They drilled horizontal shafts and from them injected vertical sheets of mortar -- basically cement grout. Santoyo says collapse is no longer is a risk. The scaffolding was removed in 1998. Why is the city sinking? The Valley of Mexico once was largely covered by several lakes, including Lake Texcoco, which measured 19 miles wide and 31 miles long. The Aztecs had built their city on an island in the lake's center, and when Spanish conquerer Hernán Cortés arrived in the early 1500s, boats were the most common form of local transportation for the indigenous people. The Spanish settlers, perhaps anxious to deprive the conquered Aztecs of the competitive advantage of their mastery of water travel, drained the lakes and built their own city on the ruins of toppled ceremonial pyramids. PASSIONATE RESTORER. To prevent flooding, they rerouted dozens of rivers that had emptied into the valley, channeling them underground and out of the valley. Today the city pumps water out of underground aquifers at a rate that exceeds their capacity to refill -- nearly 2,500 square feet of water per second. As long as that continues, the city will keep sinking as the aquifers are exhausted. "What's the biggest problem Mexico City has? Water," says billionaire businessman Carlos Slim, president of the Historic Center Trust. Possible solutions include building dams to collect river and rainwater in the western foothills surrounding Mexico City, or simply enforcing water conservation. But those are a long way off. Slim, 64, who made his fortune as a stockbroker, turnaround expert, and telecom mogul after buying Teléfonos de México (Telmex) in a 1990 privatization, is passionate about restoring the colonial downtown, where his father owned a store when Slim was young. He convinced city and federal authorities to work with the trust and give tax breaks to people willing to invest in the area. Together with a small group of fellow investors, he has bought around 60 buildings downtown and is refurbishing them. But he doesn't just want to beautify the area. He wants to create jobs and attract new residents. A PLACE TO LIVE. On a recent impromptu drive downtown, he pointed out a number of changes taking place: Behind the façade of a colonial church, in a space where old office buildings were condemned after the 1985 earthquake, the new headquarters of Mexico's Secretariat of Foreign Affairs is being built. Next door, the new, 27-story Sheraton Centro Histórico hotel was inaugurated just a year ago, a $100 million investment that features state-of-the-art anti-seismic engineering. A few blocks down, just across the street from the magnificent Belles Artes opera house, is a restored building where Slim located a department store -- he owns the Sears franchise in Mexico. Several of his companies have opened offices downtown, including a Telmex call center with 400 employees. He's making sure enough apartment buildings are renovated so that employees who want to live nearby, can. Stepped-up police patrols and the installation of security cameras have reduced crime by 36%, he says. "We want to revitalize the area so that more people will live, work, and study downtown, and that will draw all the other activities -- restaurants, stores, and so on," says Slim. Now if he can just figure out what to do about Mexico City's water problem -- to keep those colonial gems from sinking further.  By Geri Smith in Mexico City
BW MALL
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