Look down at almost any stretch of railroad track and you’ll see the same thing under the ties: a thick bed of crushed rock. It’s called ballast, and its job is to spread out the weight of whatever’s rolling over it and let rainwater drain away. Most people never give it a second thought, and frankly, that’s how it’s supposed to work.<\/p>\n
On August 23, a patch of ballast in Sheffield, England, stopped doing that job. A report from the South Yorkshire Mayoral Combined Authority (SYMCA), which runs the city’s Supertram light rail network (think a beefed-up streetcar), says the ballast under the outbound track between the White Lane and Birley Lane stops drained into a hole. It left the ties and the rail hanging over a void, and the trams stopped right away.<\/p>\n
They still haven’t come back.<\/p>\n
Supertram’s Blue route is cut between Gleadless Townend and Halfway, which takes 11 stops out of service. Blue route trams now turn around at Herdings Park, and buses cover the rest.<\/p>\n
On Thursday, the BBC’s Lucy Ashton reported that the bill for the emergency investigation and repairs has climbed to nearly \u00a31.5 million (about $2 million). SYMCA’s original estimate was somewhere between \u00a3750,000 and \u00a31 million (about $1 million to $1.3 million), and it went up after the first site investigations. Since a pound sterling buys more than a dollar, that’s a little more than it sounds like to American ears. SYMCA hasn’t given a timeline for reopening the line.<\/p>\n
An old shaft, and most likely one from Sheffield’s coal mining days. Photos The Star published in August show a brick-lined neck laid in a neat circle about 3 feet deep, with looser material below it and a small pool of water at the bottom.<\/p>\n
An 1877 map from Ordnance Survey, Britain’s official mapmaker, marks a small spot off Birley Lane, right where the tram tracks run now. An 1882 map calls it a shaft. By 1898 it’s labeled a pump, by 1939 it’s a well, and from the 1950s on it apparently isn’t marked at all.<\/p>\n
South Yorkshire Mayor Oliver Coppard has said the shaft likely dates back to the area’s coal mining, and that the track was laid right over it when this section was built in the early 1990s. He’s also said it isn’t documented in the records SYMCA has today. Which means trams have been rolling over it for more than 30 years. That’s a pretty wild thing to find out about a commute you’ve done a thousand times.<\/p>\n
How deep does it go? Nobody knows for sure yet. SYMCA says the shaft is in good shape near the top, but something blocking it further down has stopped engineers from measuring how far it goes. Records suggest it could be up to about 180 feet. That’s a figure from old paperwork, though, not a measurement anyone has taken.<\/p>\n
Then there’s a second number, and it’s easy to mix the two up.<\/p>\n
The Mining Remediation Authority<\/a> is the UK government body that deals with what Britain’s coal mining left behind, from mine water to old shafts like this one. Its legal name is still the Coal Authority, and if you want to drill into or disturb old coal workings it controls, you need its permit<\/a> before you start.<\/p>\n A spokesperson for the authority told the BBC it granted permits last week that let the investigation drill to about 197 feet. Investigators are still working out what the feature even is, the spokesperson added, and “it is too early to say what treatment will be needed.”<\/p>\n So the 197 feet is the depth the drill is allowed to reach. It isn’t the depth of the shaft. My guess is the extra 17 feet or so gives the rig room to get past the bottom the records point to, but that’s my read, not something the authority has said.<\/p>\n SYMCA’s report also says the approvals needed for work near what it calls the probable shaft complicated the investigation. I get it. Nobody wants a drill bit wandering blind into old coal workings under somebody’s neighborhood.<\/p>\n You’d think that’d be the obvious fix. But you can’t fill a hole properly until you know what it is, how deep it goes and what shape the ground around it is in, and that’s exactly what the drilling is supposed to find out.<\/p>\n Travel South Yorkshire’s November 2 update<\/a> says engineers are designing a structure to support the tracks above the shaft, with more drilling underway to plan how to fill it. Nobody’s going down for a look, either. Professor Liz Laycock of Sheffield Hallam University told the BBC that old mines can be unstable, so investigators will likely lean on boreholes and ground-penetrating radar instead.<\/p>\n Ground-penetrating radar is basically radar pointed at the dirt instead of the sky. It sends pulses into the ground and reads what bounces back, so voids and buried structures show up without anyone having to dig.<\/p>\n We covered a drill rig in south London that pushed a hole under a live railway and two tram tracks<\/a> a while back, and that job went a lot smoother, since the trams kept running the whole time. And Sheffield’s got another hole going in across town, where a tunnel boring machine is cutting a storm drain under a steel plant<\/a>.<\/p>\n Laycock thinks it’s feasible that the engineers who built Supertram about 30 years ago simply didn’t know the shaft was there. And once you hear her reasoning, it’s pretty easy to see how that happens.<\/p>\n According to Laycock, the Coal Authority knows of about 175,000 mine entries across Britain, plenty of them around Sheffield, and mine records weren’t required until 1842. Shafts are also hard to spot because the soil around them has often been disturbed, and holes can open up years later when old backfill, like timbers or planks, rots away.<\/p>\n If you live anywhere near an old coalfield, that’s a fun thing to think about at 2 a.m. Luckily, Laycock also said passengers shouldn’t be worried. She told the BBC another shaft under the tram lines is statistically very unlikely, and that tram vibrations aren’t necessarily what caused this one to open up.<\/p>\n Engineering firm VolkerRail got the job on an emergency basis and is working on the outbound rails at Birley Lane. Meanwhile, replacement buses run between Gleadless Townend and Halfway, and Supertram tickets are valid on them. Travel South Yorkshire says it added more buses after feedback from passengers.<\/p>\n That hasn’t solved everything. Local council members told the BBC that route 120 buses are often full, which leaves some people stranded at stops. Clive Betts, the member of Parliament for Sheffield South East, said the combined authority needs to make the replacement service a lot better, and pointed out that the buses often can’t take more than one wheelchair user at a time.<\/p>\n Honestly, that’s arguably the bigger headache here. The shaft will get fixed eventually, slowly and expensively, but the people who relied on those 11 stops are dealing with crowded buses every day until it does.<\/p>\n Travel South Yorkshire’s latest update, dated November 2, says the shaft’s full depth and condition are still being investigated, and that it’ll post a date for trams returning to Halfway once it has more information.<\/p>\n","protected":false},"excerpt":{"rendered":" Look down at almost any stretch of railroad track and you’ll see the same thing under the ties: a thick … <\/p>\nWhy not just pour concrete down it?<\/h2>\n
So how did a tram line end up on top of a shaft?<\/h2>\n
Riders are stuck on replacement buses<\/h2>\n