"Every time we build something we run the risk that it'll collapse." "When structures collapse people suffer." "Keeping structures up and designing ones that won't collapse is a constant challenge for architects and engineers." "If gravity had its way, everything would just fall down." "Add earthquakes, floods and high winds and the result can be destruction and death." "Engineers struggle to figure out exactly how collapses happen so they can design structures that offer safety instead of danger." "The most violent and terrifying cause of collapse that nature can throw at us is an Earthquake." "In 1995, the busy port of Kobe suffered Japan's worst earthquake in living memory." "It lasted only 20 seconds but left five and a half thousand people dead and 40,000 injured." "The quake caused more damage than any earthquake in history." "At seven point two on the Richter scale, it destroyed nearly half a million houses." "Kobe was a modern high tech city." "But the disaster destroyed all its infrastructure." "The quake took out phone and power lines, bridges, roads, police and fire stations." "All life-saving emergency systems were wrecked." "Across the Pacific in California, an earthquake like the one in Kobe will happen." "It's just a matter of where and when." "In San Francisco, the race is on to make key structures quake proof before the big one comes." "An airport is a city's lifeline to the outside world." "It needs to stay functional no matter what happens." "This is the new International Terminal at San Francisco's airport." "In 1994, during the design process, its team of architects got a rude wake-up call from Los Angeles." "Architect Craig Hartman was among those who was jolted by the alarm." "We were almost fiinished with design when the North Ridge earthquake occurred in Los Angeles." "And that earthquake like every earthquake, reveals new information about the way the earth moves, the way it works." "The destruction caused by the Northridge earthquake took everyone by surprise." "The quake weighed in at six point seven on the Richter Scale, and caused over $20 billion of damage." "Well-constructed buildings and solid concrete freeways many miles from the earthquake's epicenter were taken out with ease." "The same magnitude quake in San Francisco would have destroyed the new terminal." "When they saw what happened in Northridge," "Craig and his team went back to the drawing board." "We found that we, in fact, we should further strengthen this building to let it respond to even higher criteria...and so, instead of a" "500 year earthquake that it was originally designed for, we found that we in fact should design a building for an earthquake that might occur once every thousand years." "With every earthquake, engineers learn more about how to keep buildings standing." "They used to make structures stand rock solid against nature." "But now they've had a better idea, to roll with the punches." "In recent years we found that the more reasonable approach is to work with nature instead and to understand the way the earth moves, the way the wind acts on buildings and allow buildings to respond to that and organically adapt themselves." "Craig wanted to fiind a way for the whole huge structure to move with the quake, not against it." "Something called a friction pendulum bearing, looked like a promising solution" "Thousands of tons of building sit atop full-size versions of these bearings." "Each bearing rests in a smooth curved plate." "Nothing moves, that is, until there's an earthquake." "When the quake strikes, the ground shakes and the whole building slides safely from side to side, on the bearing." "In theory, nothing should fall down." "Craig's computer test showed it would make the structure almost indestructible." "But for a project this important he needed to be sure." "You can do all the computer technology and modeling you wish but unless you see it with your own eyes it is difficult to believe until you really see it operating." "The bearings had to be tested under real earthquake conditions." "To do this test you need a shake table." "A shake table is a slab of concrete, supported and moved by powerful hydraulics." "It can mimic actual recorded earthquakes." "No two earthquakes are the same." "The movements of different quakes as they happened for real, are programmed into the shake table." "The results were spectacular." "The model of a part of the airport terminal, slid safely around on its bearings just the way it was meant to." "So what would happen if the model was fiixed to the ground?" "To fiind out, Craig disabled the bearings and watched." "In about two minutes it collapsed." "So it was for us, a very graphic demonstration of the effectiveness of this, this technology." "But there was another problem." "The new terminal would connect with the older airport buildings that hadn't been designed to move in a quake." "It's all very well for the new terminal to rock on its bearings, but that same action would pull its neighbors down." "Craig solved that one too." "At every point of contact between the old and new buildings, the designers made what they call sacrificial joints." "When an earthquake hits, these floor panels are designed to give way, so there is nothing joining the buildings together." "Up top, the glass ceiling panels just slide across each other." "Down at the foundations, the whole structure is surrounded by a safe area, giving it room to move without bumping into its neighbors." "This is the biggest building ever constructed that isn't actually fiixed to the ground." "The whole thing floats on 267 of the new bearings." "San Francisco after an earthquake will have a functioning airport." "Even more important are the city's roads." "When a quake occurs intact roads are critical for rescue and escape." "San Francisco's road bridges are its lifelines." "If the bridges fail, rescue plans are useless." "In 1989, the nightmare came true." "The Loma Prieta earthquake measured seven point one on the Richter Scale, killed 62 people and left 12,000 homeless." "Part of the vital Oakland Bay Bridge collapsed, turning into what police called a concrete sandwich." "The Bay Bridge collapse pushed Caltrans, the state transportation department, into action." "Their engineer, Dorie Mellon, had to work out how to improve the entire" "Bay Area bridge system so it would survive the next big quake." "What we found is that we had some old and very fragile structures on our hands and we also found that they were built with unique methods that were state of the art back, you know, 60 years ago but very difficult to work with now." "And also, they were historic so we couldn't really change the way they looked." "It was a very challenging design problem." "Flexibility was the key." "The engineers needed to fiind a similar solution to the isolation technology under the new airport terminal." "Isolation means that you're separating one part of the bridge from another and you're not, the super structure is not necessarily dragging the sub-structure along with it and pulling it back and forth." "So, by de-coupling or separating the two parts of the bridge you are allowing the displacement that happens in an earthquake to happen in the place that you designed it to happen so you can accommodate it." "So Dorie started to test ways of achieving this." "Just a short drive across the bridge that started it all, is the shake table at Berkeley." "Obviously the whole Bay Bridge won't fit on the shake table but a scale model will." "Now, this is, is a simulation of a bridge and it is built at one quarter scale so this would be equivalent to a single span bridge four times as long." "Today's test is on a bearing, made of lead and rubber." "The rubber should flex in an earthquake, absorbing shock like a suspension on a car." "If it fails, the 65,000 pound concrete model will collapse." "Five, four, three, two, test." "The bridge model has to go through the same ordeal as the airport model." "A series of historical earthquake simulations that put the bearings under maximum stress." "The rubber bearing holds up and the test shows Dorie that it will help make some of San Francisco's big bridges quake proof." "But nature won't necessarily wait for all the work to be done before it decides to let loose another earthquake." "The challenge is not just technological." "It's logistical as well." "There's only so many welders in California, there's only so much steel." "We're having to import a lot of our steel; we just can't get it locally." "So, that drives the cost of the construction up." "So, we have challenges, not only in how to retro-fit these bridges and do it quickly, but also just how to fiind resources for all these projects in a very limited amount of time." "The tests proved that installing bearings can protect the bridges in and out of San Francisco." "Unless of course the quake is even more violent than the worst that can be anticipated." "Any large earthquake is getting to the point where it is just excessive." "You would have dramatic disasters all over the area." "So, whether or not your bridge is standing at the end of that event, nobody would be alive to see it." "Short of the ultimate disaster," "San Francisco's bridges should now hold up when nature's stress test hits." "But thousands of bridges are in danger of collapse all over the country." "Just because they're are old or worn out." "The Federal Highway Administration has classified 93,000 bridges as structurally deficient." "Connecticut, 1983." "A 1 00-foot section of Highway 95 plunged into the muddy Mianus River, killing three people." "90,000 vehicles a day used to pour across the bridge, and for a year beforehand locals had heard it complaining." "We hear thumps in the bridge, the joints become loose, it causes an unusual sound." "There are two ways to make these old bridges safe." "One is to take them out and start again." "The other involves fiinding ways to test the existing structure." "Everything has a design life, a kind of use-by date for engineering." "Commonly, it's fifty years, but many bridges have seen solid service for much longer than that." "The key is knowing the difference between an old bridge that's perfectly safe, and one that's going to fall down." "The George Washington Bridge, linking New York and New Jersey, is one of America's great suspension bridges." "Like thousands of other bridges it's officially beyond its design life." "Maintaining this engineering landmark is both a challenge and a privilege for engineer Peter Rinaldi." "This bridge was built in 1931, it was opened to traffic." "At the time it was constructed, it was the largest suspension bridge in the world." "It more than doubled the span of any known suspension bridge at that time." "It was a modern marvel, no one had ever built a bridge this big to carry this much traffic." "Today it's the world's busiest, carrying over a quarter of a million vehicles every day." "The world's busiest bridge is showing her age on the surface, but is the problem more than skin deep?" "The whole structure is currently undergoing a major stress test to fiind out how wear and tear are affecting the main support sections." "Like doctors doing a check-up," "Peter and his team are dissecting and inspecting the most stressed parts of the bridge." "The cables." "Being a suspension bridge, the cables are fundamental to its strength." "Everything literally hangs on them." "Hanging from the four main cables are 640 steel suspender ropes." "Each one carries almost 130 tons of load." "They've been doing this 24 hours a day every day since 1931." "To see how much longer they will hold up, the engineers need to analyze them in a lab." "There, scientists will look for signs of fatigue, corrosion and even molecular change in the steel itself." "But first, they have to physically remove some of the ropes." "Without the bridge collapsing." "For the first time we're removing a set of ropes to inspect them, test them, and try and estimate their condition, and how much life they have remaining on this bridge." "It's a tricky job to remove the ropes without weakening the bridge's structure." "Here in this particular location what we've done is something rather unique, which we've never done on the bridge before." "We've removed both ropes, and to do that, the ropes are right over here in the center going down connecting." "We had to build a temporary mechanism to hold up the entire bridge, while we were removing those ropes." "And if you look over here what you can see, this is one pair of temporary suspender ropes going up on this side, and we have a similar pair right over on the other side." "While the suspender ropes are off at the lab," "Peter continues the bridge's check-up by giving the main cables a thorough internal inspection." "There's no way one of these cables can be removed, so for this test, science had to come to the bridge." "High above the roadway Peter Rinaldi and his team have built a portable Lab, clinging to the main suspension cable." "With some suspender ropes now missing they can remove the giant cable cover and look inside." "The covers have been locked in place since the bridge was built." "Now, for the first time, bridge engineers can examine the makeup of the main suspension cable and check the effects of over 70 years of stress." "Hidden under the cover anything could have happened to the cable." "It's made up of 1 7,000 small wires, and Peter and his team check that each one, right through to the core, is sound." "Each one of these wires carries almost a ton, about 1 500 pounds plus, in each individual wire here, so they're highly stressed." "They carry the entire weight of the bridge in these four cables." "Sample wires are cut and sent for testing." "Step by step, a picture of the bridge's well being is built up." "Actually we're surprised, we're fiinding the cable to be in much better condition than we expected we were anticipating the worst, but that's not the case, the bridge is in excellent shape." "We found a little bit of rusting at the top of the wires but as we look in there's still much of the galvanizing is there and the wires seem to be in very good shape." "Matter of fact you can still see some of the original, red paint that was put on here when the bridge was constructed it's still here." "This is not rust, it's actually the color of the paint that was put on the bridge originally to protect it." "The old technology is holding up." "It's forensic engineering and I fiind it exciting that we're able to take a look at the condition of this bridge, built by the engineers that went before us, and hopefully we'll be able to keep it in as good condition as" "when they built it." "The tests will help engineers keep a fiinger on the pulse of one of" "Manhattan's main arteries, and save it from collapse well into the future." "I'm convinced that it easily has another 70 years." "Especially if we keep up the maintenance and the kind of care that we've been giving this structure." "I know that my great, great grandchildren will be travelling over this bridge." "All bridges are vulnerable to one particular force that can lead to collapse." "That force is wind." "While the George Washington bridge raised depression-era spirits on the east coast, a disaster was in the making on the west." "A huge new suspension bridge spanning Washington State's Tacoma Narrows was opened in 1940." "Renowned engineer Leon Moysieff couldn't have known at the time that his elegant bridge was about to become famous for all the wrong reasons." "The bridge was to star in some of the most spectacular fiilm footage ever shot." "And it would change the science of stress testing forever." "The dramatic collapse of 'Galloping Gertie' as she was known shook the engineering community to the core." "World-class engineers just didn't make mistakes like that." "People in those days did not really nderstand fully how to handle the fact that the wind is very turbulent." "Everyone knew that there were gusts but how to actually fit that into the design of a building wasn't clear." "Ostensibly that bridge had been designed to withstand winds much, much higher but they were static winds, just a steady horizontal force, not a wind that grabbed the bridge and made it twist and bounce up and down." "On the heels of the collapse, the world of stress testing entered a whole new era." "The remains of the bridge were used for a one-time experiment." "Engineers released trails of smoke at different points along the bridge's structure." "The smoke showed exactly how the wind was moving around the bridge." "The testers were witnessing a previously unknown turbulence that had not been factored into the bridge's design." "Fascinated, they made a model of the bridge, put it in a controlled space, and blew wind across it." "This was the birth of modern wind tunnel testing." "The test told engineers that the Tacoma Narrows bridge was too thin to remain stable in turbulent winds." "The collapse of 'Galloping Gertie' revolutionized the understanding of how wind works." "In the 1950s, ideas began to develop about what, what is called the planetary boundary layer." "This is the layer of wind blowing close to the earth's surface that really was quite, quite a big landmark." "This boundary layer of wind is what we feel on the ground." "It's made turbulent by anything in its path, man-made structures, mountains, even trees." "It's so complex and unpredictable that there's still no mathematical model for it." "Boundary Layer Wind Tunnels, such as this one in Canada, help engineers design structures that won't collapse in the wind." "Hundreds of small cubes on the floor of the tunnel stir up the wind to create the boundary layer effect in exactly the same way that trees and buildings do on the earth's surface." "Today they're testing a model of downtown Chicago." "The engineers want to make sure that a proposed new skyscraper will stay upright in the windy city." "There's a lot at stake." "The results of this test will affect Chicago's skyline, and could help break a world record." "This is no ordinary building." "At a cloud piercing hundred and eight stories it will be the world's tallest." "As well as making sure it won't collapse, they will look at how the building itself affects the boundary layer." "Skyscrapers can funnel strong winds down to street level." "The wind created by some of the older ones has blown pedestrians right off their feet." "More recently, wind tunnel tests have shown designers, that rounding the corners of these towers reduces the turbulence, creating more people friendly cities." "These days all large structures are tested in wind tunnels." "No engineer wants to be responsible for another collapse like" "'Galloping Gertie'." "And I think that's a very good lesson for us all to learn, is that, when we're constructing our elaborate mathematical theories, is that we always have to be aware that we are making assumptions when we do that." "And that there could be, again, some other phenomenon, which we're totally unaware of that could come and take us by surprise." "You really don't want to wait until you've invested all those maybe hundreds of millions of dollars in this massive structure, and then fiind out that you've missed something." "If that structure happens to be a dam, holding back trillions of gallons of water, all the more reason to get the calculations right." "Many of them pose a threat to the people living below then and need to be tested for safety." "Essentially, once you build a dam you've created a hazard you've created the potential for a catastrophe if the dam fails and people, the public and construction, is downstream." "On December 1 4th, 1963, someone spotted a crack in the concrete rim of a dam above the" "Baldwin Hills section of Los Angeles." "Within two hours, that crack was a seventy-foot gash from crest to foundation, and the community was under water." "The flood wave carried buildings in its path." "The police desperately tried to evacuate homes below the dam." "The burst Baldwin Hills reservoir, last night, wiped out Cloverdale Avenue completely." "Washed 60 thousand-dollar homes off that pad down the street." "Left a scene of absolute devastation behind it." "Here on the flat land across the street is the Village Green Apartments, just devastated by the mud and high water." "A wave of mud and debris washed away 277 homes." "Thanks to the early warning, most people managed to get away before the flood hit." "But five people lost their lives in the torrent." "The community of Baldwin Hills was destroyed." "It took many years, and over twelve billion dollars, to recover." "The dam was never rebuilt." "Crumbling and cracking concrete is a dam surveyor's nightmare." "Many dams that pose a threat are from the boom years of concrete construction." "Back then, the science of long-lasting concrete was in its infancy." "For older dams where the engineering and science of concrete materials was not well developed." "The aggregates or the cements that were used may not have been up to our modern standards." "In some cases those dams may develop problems with the materials in the interior of the dams, we're looking for that." "Concrete dams work like bridges lying on their sides." "The arch of the dam is the key to its strength." "Just as the arch of a bridge carries weight from above, the arch of a dam holds back the weight of the water." "The water puts enormous pressure on the concrete." "Concrete is a material that performs very well in compression, which is what the curvature or the arched structure does, it puts the concrete into compression." "It can withstand a whole lot more compressive forces than the designers rely on it for." "Here in Denver they test concrete to the breaking point." "To fiind out how safe any particular dam is Frank McLean checks the strength of different concrete mixes." "This giant hunk of steel is a universal testing machine." "Its party trick is to test the strength of building materials, exerting up to 25,000 tons of brute force on to whatever's being tested." "Today, its victim is a concrete cylinder, and a bunch of student dam engineers have gathered to see what the monster will do to it." "The compressive stress now is the key and it of course is the most common test for concrete." "In a dam, most of the loading is a compressive loading, so we will take then, fail this specimen and determine the strength of the concrete itself." "The machine presses down on the concrete, applying around one million pounds of pressure per inch per minute." "They're looking for the point where it gives." "And we're currently at one point two-five million pounds." "And the cylinder is starting to strain a lot, we are getting near failure." "Get ready to jump." "Get ready to jump." "That is up there." "Now this shows the maximum load that the cylinder failed at, approximately two point seven-nine million pounds." "That's sufficient strength for any dam." "Nowadays all concrete mixes are put through this test to make sure that dams are built to last." "But not all dams are made of concrete." "For each individual site there may be an optimum dam design where one considers the function of the dam and the economics of the project." "There's no such thing as a single ultimate design for a dam that will fit any site." "The traditional way to hold backwater is with earth." "But unfortunately, when earth dams are breached, total collapse is inevitable." "One night in March 1996 the New Hampshire town of Alton had its peace shattered by the collapse of an earth dam." "Two local fire fighters did what they could for their neighbors, even as their own homes were under threat." "I was in the house and I looked out the window and I could see water all the way across the road." "And my wife said the water main's broke and I said no, too much water for a water main, the dam's gotta be gone." "We heard the terrible crashing coming down through the woods, and then, you know, probably fifteen to thirty seconds after we heard the initial crashing and things like that, then we saw the onset of water come down." "A neighbor and her husband were going down the road to try to escape the path of the water." "The gentleman driving his 1 8-wheeled tractor-trailer truck, and the road basically washed away underneath his truck." "The truck was right outside John's house." "His training as a fire fighter allowed him to act quickly and save the driver from drowning." "My wife hollered and said somebody was hollering for help." "So I came out here on my steps and then I went back in my garage and I got a rope and threw it to him out there." "And he tied it around his waist and he jumped off into the water." "And it was probably six, seven, eight feet deep at that time." "When we pulled him up through here you know, he was, you know, just like a wet rag, you know, just limp." "Tragically the force of the water carried the man's wife away before the rescuers could save her." "Her pickup truck was washed off the road, and down in back of this property here." "We found her, I guess basically, a week later." "So that was the worst part of the whole deal, is the loss of life." "Daylight revealed the extent of the damage." "In the space of fifteen minutes, the dam had sent its lethal cargo of eleven million gallons of water hurtling down the hill, smashing buildings and ripping up the road." "This was just one of twenty-three dam collapses to take lives since 1960." "Most dams that suffer catastrophic failure are made of earth." "Scientists are currently investigating why earth dams fail." "One of the main problems is internal erosion of the soil, which can lead to depressions called, sinkholes." "If erosion happens below the surface, a hole will develop." "Any earth sitting on top of the hole will obey the laws of gravity and fall in, leaving a sinkhole." "Water under pressure always looks for a way out and a sinkhole can provide just the weak point it's looking for." "At the University of Colorado in Boulder, experts believe that by studying the way sinkholes form, they may be able to prevent disastrous dam breaches in the future." "To simulate the combined effects of time and gravity on a massive structure calls for a very special kind of stress test." "In this concrete-lined, reinforced basement, is a giant centrifuge." "Centrifuges increase the force of gravity by spinning at exceptionally high speeds." "This test will determine how much force it takes to create a sinkhole." "They're using a scale model of a 60 feet earth dam." "X marks the spot where the earth has been weakened below the surface." "This is where they expect a sinkhole to form." "This is probably one of the three most powerful centrifuges in the world for geotechnical testing." "To get to 200 G's the centrifuge will have to spin at 200 revolutions per minute, about three revolutions per second, and you can see it's pretty fast." "The model is placed in the centrifuge and everyone leaves for the safety of the control room." "If anything went wrong with the machine and it spun out of control, the force produced could wreck the building, killing any bystanders." "The centrifuge gets to work, picking up speed until the dam model is stressed by 72 times the normal force of gravity." "In Boulder they proved that a centrifuge is the most accurate way to test these huge structures." "You can do it in full scale, which would be very expensive, or you can do numerical analysis, but there's always some doubt, as to how accurate those analyses may be." "At 12 Gs a human body would give up." "At 72 Gs so does the dam." "In fifteen minutes the engineers can see fifty years of stress." "The information from this test will be available to all dam designers." "They can take advantage of our fiindings and try to refiine their design in hopefully a safer and more cost-effective manner" "Stress testing dam design can save lives." "It also tells designers how to prevent sinkholes from forming in the first place." "Ironically, dam engineers can sometimes use sinkholes to their advantage." "The Auburn Coffer Dam in California was built with this in mind." "A section of the dam was deliberately designed to fail first in the event of a flood." "It's a kind of safety valve." "The floods of 1986 put it to the test." "Water spilled over the dam and eroded the artificial sinkhole as planned." "The safety valve worked!" "The water took the path of least resistance." "The path the engineers had made for it." "Away from people and their homes." "This design also provided enough time to empty reservoirs down stream, making room for the excess floodwater." "But sinkholes will also occur wherever the soil is loose, or where underground excavation hasn't been properly reinforced." "In a winter storm in 1995, San Francisco's exclusive Sea Cliff community discovered just how bad a sinkhole collapse can be." "There was a storm on December 11, 1995 that led to a major collapse of a sewer, several hundred feet of a 1 00-year-old brick sewer." "This empty lot once held a 3 million-dollar house." "On the night of the storm, a sinkhole between the damaged sewer and the house led to one of the most dramatic collapses ever caught on camera." "As the gushing sewer scoured soil from the expanding sinkhole, local families fled their homes." "Things were happening really fast, huge car sized parts of the pavement were falling in." "Everything collapsed in one giant whooh, and it was like, Ok, time to go." "At the moment the sinkhole has swallowed up a good half block of pavement, a pickup truck, one garage, two home foundations, and it's now threatening to take an entire home out as well." "Being by the sea the house was built on sand, which is no match for high-pressure water." "Okay, you can still see it." "There's lots of water pouring out of the sewer." "Yeah, we can just see here over on the right there's more dirt falling away from underneath the foundation." "Yeah, I don't think we should stand too close if we can, it can be quite dangerous." "Yeah, that's a good idea, I think we're gonna move away from here, thank you very much." "Gary, I just wanted to ask you..." "Oh and there it goes" "Oh my gosh." "Oh my gosh, wow." "The entire house and its contents were lost to the hole." "They found nothing." "They never found the jewelry." "They never found the Mercedes that was buried somewhere under there, which I thought was remarkable." "Two things combined on that fateful night." "Somehow the sewer had become pressurized." "Water under pressure seeks the easiest means of escape." "In this case, it found a sinkhole." "As people who had lost their homes tried to get their lives back together," "Ed Medley pieced together the chain of events that led to the collapse." "Part of the mystery was why did the sewer get pressurized, why, why did it, why did it load up as so much water pressure." "Ed had a hunch he'd fiind an answer down in the sewers." "The hunch paid off." "He discovered that the sinkhole had been caused by underground construction work between the sewer and the house eighteen months before." "A few streets back he found another culprit." "More construction work that had partly blocked the sewer." "The two in combination had led to the calamity." "And it's a bit like having a garden hose with water just gently flowing out." "And, and, the structure is like you putting your foot on the garden hose, pressing down on the hose and if you can imagine you having little holes in your pipe, suddenly the water started to spurt out of the holes in your hose." "One end of the hose was the sewer outflow to the ocean." "This outlet was blocked by the construction work so the water couldn't escape." "The water backed up, and up, and up until it arrived at the sinkhole." "So it all started because of the conjunction of, there was pressure and there was a sinkhole." "The old brick sewer, now full of storm water, was under extreme pressure because of the blockage." "To make things worse, the sinkhole meant that this sewer was no longer weighted down by tons of soil." "Brick sewers work because of the weight of soil around them and so taking away the weight of the soil as just above in the sinkhole, meant that it was vulnerable should there be any pressurization." "When the pressure became too great the sewer burst, gushing wastewater into the sinkhole." "This water scoured away a bigger hole in the sandy soil." "The inevitable result was that the ground collapsed, along with everything above it." "When Ed fiinally pieced together the whole story he realized it was a very unlucky accident." "In the case of this hundred year old sewer the designers and builders of these sewers never, ever possibly could have conceived of the fact of construction" "1 00 years later in two completely different places coming together that night." "For Ed, the collapse of a multi million dollar home because of a decaying Victorian sewer, is a timely warning." "Things tend to have a much longer life than we originally designed for." "And so, the infrastructure can't last forever." "And so we should be concerned that one-day parts of our infrastructure are going to collapse." "The world we have built is getting older, and the stresses and strains of nature never cease." "Science is working hard to balance nature with construction, and stay in control of collapse."