This month, a project a decade in the making wrapped.
On May 8, Section 1 of the Los Angeles D Line Subway Extension Project, formerly known as the Purple Line, opened. The roughly 4-mile addition created three new underground stations, including one beneath Wilshire Boulevard, one of the highest traffic roads in L.A.
Digging two tunnels to build three stations in a densely populated area provided a creative challenge for the Skanska Traylor Shea joint venture, which built the $2.4 billion Section 1. All told, 7,141 construction workers labored on the job.
Here, Geoffrey Bender, project executive of operations at Skanska USA Civil, talks with Construction Dive about the challenges of a 10-year project, working on a transit job in a crowded city and the items the builder unearthed.
Editor’s Note: The following has been edited for brevity and clarity.
CONSTRUCTION DIVE: What kind of planning and coordination is required for a project like this that takes 10 years?
GEOFFREY BENDER: We had four miles but two tunnels, so really eight track miles. The coordination with all of the stakeholders in order to even be able to break ground was a task in itself. I like to tell people about every two years, it seemed like my job was changing.
For example, we had to excavate the first station down in order to launch the tunnel boring machines. Of course, we did a lot of utility work. That was the first phase. The next phase was installing an outline of the station using steel piles a hundred-plus feet deep, which were drilled in.
After a year or so doing that, we started the excavation, and that took about two years of shoring. Then we were finally able to launch the tunnel boring machines. Once they were launched, we then focused on the other two big station excavations.
After all that rough-in work, the tunnel boring is done, the station excavation is done. Then mass concrete starts. Once the mass concrete is done, then we start talking about architectural mechanical finishes and all the ventilation that has to go in. Then after that's all done, we're laying rail, we're putting down the system that actually runs the train. That's how we get to the 10 years.
It's a lot of work that's concentrated into one project.
The project brought the team under Wilshire Boulevard, a high-traffic area. Did that pose challenges for the project?
It was definitely one of the most complex parts. When you talk about Wilshire Boulevard, you got to talk about the urban density and the utility construction and coordination that was required to bring all those different utility services to the people in the area.
We’re talking sewer, electrical, water, gas, telecommunication, they're all under our corridor here, even some oil pipelines. We combated that with a lot of utility mapping verification and how we phased the work.
One of the more complex things was actually what Mother Earth gave us to tunnel in. In the area we were tunneling, we had a very high variety of soil conditions. Typical to central L.A., we had a lot of mixed soils. We had a lot of groundwater.
One odd thing about this job is we tunneled through and we built a station in the tar sands geology. You’ve probably heard of the LaBrea Tar Pits. We had a lot of potential issues with gas and the soil conditions in the offgassing. In the reach that went through the tar sands, we had about 200-plus gas alerts during the mining itself, where we had to clear out the machines, pull everybody out, get approval from CalOSHA in order to go back to work. So that's very different from what you would see on a typical tunneling job.
How long does that process take?
It’s funny. Like everything, when it happened the first couple of times, we had to come out of the tunnel and get cleared by CalOSHA to go back to work. That would take hours. After about the 150th time, it was a 10 minute call. We had seen it so many times before, CalOSHA allowed us to go back to work almost instantly.
In the excavation work, the team found over 500 ice age fossils. What’s it like to come across those during construction?
It was during the station excavations where we found all of the fossils.
We have paleontologists on site with us at all times. The first couple discoveries were a big deal. As we got deeper, unless it was a new type of animal bone, we still kept them, of course, but it wasn't as big of a deal.
Now, I will tell you one of the things here at the La Brea station, we did find a mastodon skull almost completely intact. It was only about 15 feet deep. And because we have paleontologists on site, we actually boxed it up, used a tree box and saved all the earth and everything around the fossil and were able to transport that to our natural history museum here in town.
So which was more of a cause for delays: Fossil discovery or the CalOSHA calls?
It was definitely the CalOSHA calls, just because of the sheer number of them.
