Apparently it uses two cutting heads, interlocked like gears, to bore double-barreled tunnels over a narrower area and ostensibly with less waste. The tunnel takes the form of union Venn diagram, with a line of columns in the middle.
For tunnels, it’s not an unusual configuration. Tunnels are round because it distributes weight forces efficiently and because a rotating cutter head involves the fewest moving parts. But, this also often leaves space that’s hard to use, since most vehicles are rectangular in section. Intersecting the circles creates flat sides and reduces waste.
But as far as I know, TBMs like this are rare. A technical paper I found explains some of the difficulties, but there are TBMs with 40- and 60-foot diameters, such as Bertha, used to tunnel the Alaskan Way Viaduct replacement, or what Tysons Tunnel proposed.
I have no idea about the feasibility or actual value. I’d love to find out more.
Landscape-oriented architecture blog Pruned is carrying an excellent post about the wastewater-recovering wetland installed at the center of their new campus. The LEED Platinum building, which opened in 2007, was designed by KieranTimberlake of Philadelphia. The firm designed the building to recycle all of its graywater and brownwater through an elaborate wetland, as one of its many sustainable features. If you go visit the building, the trickle filter is wrapped with a sign that explains how the system works. The sign rests at a child’s height and leads readers around and around with arrows, which I find a little obnoxious. Luckily, Pruned has explained the process more clearly, so without further ado, go read their article.
Pruned also notes a very important civic issue this solves: the cost of runoff on municipalities and local watersheds. This beautiful oasis reduces the amount of water that flows out of the building, or flows off the hard surfaces of the building (there is a separate rainwater recycling system), and into Rock Creek and the White Plains treatment facility. Among the general public, a lot is made of water conservation (which this building also assists), but the strain on public facilities caused by sewage and stormwater is quite severe. At least up in Cleveland Park and Tobago, we do not have combined sewer overflow systems, like the do downtown.
For elite Washingtonians worried that their children will become astronauts or mutant mer-men, the recycled water is dyed blue with a non-toxic coloring agent and reused in toilets and janitorial sinks. Meanwhile, St. Albans School’s non-LEED Marriott Hall, by SOM is in the interior-fit out phase, and has just gained its green roofs. More on that some other time.