Ask a mechanic about remanufactured engines and you’ll probably get a pretty enthusiastic answer. A reman engine is an old block that’s been stripped down, cleaned up, machined and rebuilt with new wear parts. It usually costs less than a brand-new crate engine and shows up a lot sooner, and once it’s bolted in, most drivers never know the difference.<\/p>\n
It turns out the people digging Paris’s new subway feel pretty much the same way about tunnel boring machines.<\/p>\n
On October 7, the Soci\u00e9t\u00e9 des grands projets, the French state agency building the Grand Paris Express (it used to be called the Soci\u00e9t\u00e9 du Grand Paris), held a naming ceremony in Gennevilliers, just northwest of Paris, for a machine called Roberta. She weighs about 2,200 tons, her cutting wheel is just over 32 feet across, and she’s lined up for roughly 4.3 miles of new metro tunnel.<\/p>\n
She’s also not new, not by a long shot.<\/p>\n
Until this week, Roberta went by Houda. Under that name, she spent more than three years grinding out about 3.6 miles of Line 16, another Grand Paris Express route, under the suburbs northeast of the city. She was the last of that line’s seven machines to finish, breaking into her exit shaft at a site called Mare au Chanvre a little over two and a half years ago.<\/p>\n
That’s usually where a tunnel borer’s story ends. When we covered Virginie, the Line 17 machine that tunneled under Charles de Gaulle airport<\/a>, nobody had said yet whether she’d be scrapped or rebuilt. Houda got the rebuild.<\/p>\n Crews took her apart and shipped her to Terni, in central Italy, where Webuild, one of the contractors on her new job, runs a facility that specializes in overhauling big tunneling machines. According to Tunnel Business Magazine<\/a>, she got a complete overhaul, some updated technology and modifications to suit the ground on her new route.<\/p>\n So how do you get a 187-ton cutting wheel from central Italy to the edge of Paris?<\/p>\n Slowly, and arguably that trip is the most impressive part of this whole story. The contractors say<\/a> the logistics chain ran about 1,370 miles. Her heaviest components, that wheel included, shipped out of Civitavecchia, a port up the coast from Rome, and made the rest of the trip by truck, ship and barge. She got to Gennevilliers in late August.<\/p>\n Nobody’s said which ports or rivers she used along the way. Frankly, I’d have paid good money to watch a 187-ton wheel float past on a barge.<\/p>\n As for the new name, it honors Roberta Arrigoni, a Webuild architect who’s spent 37 years on big, complicated infrastructure jobs and has been part of the Grand Paris Express from the start. French tunnel crews traditionally give their machines women’s names, a nod to Saint Barbara, the patron saint of miners. This one’s now had two.<\/p>\n Mostly because it takes forever. Tunnel boring machines aren’t really something you pick up off a lot. Each one’s basically set up for the specific ground it’s going to chew through, and that tends to take a while before a single foot of tunnel gets dug.<\/p>\n The contractors say rebuilding Houda saved about 12 months over building a new machine from scratch, and that it also cut costs and carbon emissions. They haven’t put a number on the money, though.<\/p>\n A year matters here. Line 15 will be a ring all the way around Paris, the longest metro line in the country, and the western stretch Roberta’s working on is scheduled to open by the end of 2031. Once it does, the contractors say, riders will get from Saint-Denis Pleyel to La D\u00e9fense, the big business district on the city’s west side, in 19 minutes.<\/p>\n Reusing a borer isn’t a new idea, by the way. We’ve written about one that sat on the surface for 11 years before heading back underground in Arizona<\/a>. But shipping a 2,200-ton machine to another country for a rebuild and then shipping it back is a pretty serious commitment, and I’d say it beats leaving one to rust in a yard.<\/p>\nSo why not just build a new one?<\/h2>\n
So what is an earth pressure balance machine?<\/h2>\n