BETHESDA, Md. — Cranes towering overhead and crews toiling dozens of feet below ground mark the spot just off Wisconsin Avenue that will serve as the western end of the Purple Line.
Work on the Bethesda station and the direct elevator connection to the Red Line platform below will soon trigger blasting at the site of the old Apex Building at Wisconsin Avenue and Elm Street.
The Purple Line construction team is about 24 feet deep on what will eventually be a 150-foot shaft for an elevator bank, improved ventilation for the Metro station and the connection to a cavern that will serve as the Purple Line stop’s mezzanine. The shaft will also be the connection for a second entrance to the Bethesda Metro station, far below the Purple Line tracks.
Around 60 feet below ground, Purple Line tunneling project manager Jean-Marc Wehrli said, crews expect to hit bedrock.
That means explosive blasting is planned for the shaft beginning next month.
“We’re trying to blast early in the morning every day, so that’s going to be starting sometime in October, going all the way through probably late 2019,” Wehrli said.
The precise amount of explosive needed for each 5 or 6 a.m. blast will be trucked in each day from West Virginia.
“The amount of explosives we need here to blast this cavern in rock, you’re just not allowed to store such a big amount of explosives here in Bethesda. It’s just too much of a risk for the residents and to commercial buildings around here,” Wehrli said.
Like the work along the entire Purple Line route, this construction is being done right next to and across from existing buildings that house offices, apartments and hotel rooms. The project has promised to remain within tight limits on vibration and noise to prevent any damage to the buildings or Metro line below, as well as to reduce the significant inconvenience of five years of construction work.
“You’re not going to feel anything; you’re probably going to hear a little bit of a rumble,” Wehrli said of the Bethesda blasting.
“Right now we’re only working during daytime, but later, once we hit rock, we’re going to go for a three-shift operation. This means 24 hours a day, five days a week,” he said.
Crews are also separately working on the only other tunneling on the project, near Flower Avenue in Silver Spring.
Purple Line Transit Partners has promised to send out construction alerts ahead of any explosives use. Road closures are growing along the length of the line, mainly for utility relocation and other work required to prepare to install tracks and a rebuilt trail.
The Bethesda station itself will be where the trail under Wisconsin Avenue used to be, in a box underneath a skyscraper that is under construction. That box is scheduled to be completed and handed over to the Purple Line team by March to begin work on the platforms, tracks, escalators and other features.
When the trains eventually pull out toward New Carrollton, they will emerge above ground almost immediately, right after crossing beneath Wisconsin Avenue. The avenue is already carried over the eventual path of the tracks by a bridge that was built to accommodate the Purple Line years ago.
The 16-mile, 21-stop light rail line is not a part of the Metro system, but has key connections to the heavy rail system at Bethesda, Silver Spring, College Park and New Carrollton. The Purple Line is scheduled to open in 2022.