Central Link Section 710
Seattle, Wash.
The Emerald Mole boring machine.
Whether or not you're a believer in the universal benefits of public transit, this project deserves respect. To build a passenger rail station in the Beacon Hill area, south of downtown Seattle, contractors had to create the largest and deepest soft-ground sequential excavation method (SEM) tunnels in North America. SEM refers to the practice of digging a tunnel in sections, supporting each segment as you go. The pair of mile-long tunnels—part of a 14-mile light-rail project—were nearly twice the depth and diameter of previous such projects, running under a 352-feet-high hill. When initial test shafts found a surprisingly large amount of fine sand, engineers quickly rearranged the design and path of the tunnels, pioneering new construction techniques that should benefit future SEM projects in soft soils. The final result is inherently unassuming—the Beacon Hill station is 160 feet underground, accessible in 20 seconds by elevator—so the 642-ton, 330-feet-long earth-pressure-balancing tunnel-boring machine that dug the tunnels will have to stand testament to this nimble and literally ground-breaking project.
Concordia University Wisconsin Lakeshore Environmental Enhancement and Education Project
Mequon, Wis.
This is one of the smallest of the projects submitted to the jury, but also one of the smartest. Concordia University Wisconsin (CUW) asked engineers to counter an eroding shoreline—some 20,000 tons of sediment lost annually—while also increasing public lake-front access. The $7.6 million project stabilized a 130-feet-high, 2300-feet-long bluff along the eastern shore of Lake Michigan, with protective features that appear completely natural. Boulders strategically placed in the water serve as armor stones, breaking up the power of incoming waves, while a perched wetland area absorbs storm water. Without looking at before-and-after photos, it would be easy to assume this area was always naturally reinforced, and not the work of extensive 3D CAD and hydraulic computer modeling, water-tank testing and careful placement of 100,000 tons of rock, stone, and plants.
Metropolitan Water District of Southern California Arrowhead Tunnels
Hemet, Calif.
Water is a big deal in Southern California, where demand for it continues to climb, and experts fear a major earthquake could trigger a dangerous shortage of drinking water. The 2009 OCEA winner Orange County's Groundwater Replenishing System helped tackle the first part of that equation, increasing supply by purifying wastewater. The Arrowhead Tunnels are designed to boost supply and also to prepare for the worst. The combined 9.6 miles of tunnels can provide six months of emergency water for some 15 million residents. The impetus for this section of the 44-mile-long Inland Feeder project was also its biggest challenge—the tunnels run east of the San Andreas fault, and through 20 fault zones. Similar to the Seattle project, this one required new drilling techniques, including the use of probe holes to assess ground conditions ahead of the huge tunnel-boring machines (TBM). Thanks to the new probing system, as well as the use of strain gauges to actively monitor tunnel pressure, the TBMs were able to dig faster, with fewer stops and starts. The real test of the tunnels will be their ability to stand up to a quake and support the local populace during the aftermath. But for now, this complex and difficult project appears to be $500 million dollars well spent.
Sutong Bridge
Jiangsu Province, China
Like it or not, the current home of the state-of-the-art civil engineering megaproject is China, where the Shanghai Financial Center has recently become the second-tallest building on the planet. Even more visible, though, is the Sutong Bridge, which at 1088 meters (3570 feet) is the world's longest cable-stayed bridge, and the first whose main span exceeds 1000 meters. Engineering "firsts," though expensive and the cause of national pride, can be short on purpose, aesthetics or real innovation. The Sutong is another story: This stunning bridge replaces a cumbersome and potentially dangerous 4-hour ferry ride between Nantong and Shanghai with a 1-hour drive, and the project utilizes a new kind of zinc-galvanized-steel strand that reduces the diameter of its cables, cutting wind drag. Building a bridge in the Yangtze River meant breaking another record—at 120 meters, the Sutong has the deepest foundation of any cable-stayed bridge. As for whether the concrete and steel bridge towers needed to be 300 meters—breaking yet another record—sometimes the most responsible engineers can get a little carried away.
Utah State Capitol Seismic Base Isolation and Restoration
Salt Lake City, Utah
When the Utah State Capitol building, located several hundred feet from an active fault capable of a magnitude 7.3 earthquake, failed seismic evaluations, state authorities had two choices. Either replace the entire building, at a cost of up to $1 billion, or figure out a way to reinforce and base-isolate—making the building essentially float on its foundations—an architectural masterpiece that's more than a century old. The latter meant tackling one of the biggest and most delicate base-isolation projects to date. Because of the nature of the structure and the age of its concrete, the foundations would have to be pulled out without raising or lowering the 132-million-pound-building by more than 1/16th of an inch. Ultimately, contractors surgically installed 265 base isolators, while reinforcing the iconic dome and other structural elements. The project cost a comparatively modest $212 million, and turned what was a disaster waiting to happen into one of the most earthquake-resistant buildings in the country.
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