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This month, a project a decade in the making.
Section 1 of the Los Angeles D Line subway extension project, formerly known as the Purple Line, opened on May 8. The roughly 4-mile addition created three new subway stations, including one under Wilshire Boulevard, one of LA’s busiest thoroughfares.
Excavating two tunnels to build three stations in a densely populated area posed a creative challenge for the Skanska Traylor Shea joint venture, which built the $2.4 billion Section 1. In all, 7,141 construction workers worked on the job.
Here, Geoffrey Bender, project operations executive at Skanska USA Civil, talks to Construction Dive about the challenges of a 10-year project, working on a traffic job in a crowded city, and the elements the builder discovered.
Editor’s note: The following has been edited for brevity and clarity.
Immersion in CONSTRUCTION: What kind of planning and coordination is required for a project like this that lasts 10 years?
GEOFFREY BENDER: We had four miles but two tunnels, so really eight miles of track. Coordinating with all the stakeholders to even move forward was a task in itself. I like to tell people that every couple of years, my job seemed to be changing.
For example, we had to excavate the first station to start the tunnel boring machines. Of course, we did a lot of utility work. This was the first phase. The next phase was the installation of a station outline with steel piles about a hundred feet deep, which were drilled.
After a year or so of doing this, we started digging, and that took about two years of shoring. Then we were finally able to start the TBMs. Once they were up and running, we focused on the station’s other two major digs.
After all this rough work, the tunnel is made, the station is excavated. Then the mass concrete begins. Once the mass concrete is done, we start talking about mechanical architectural finishes and all the ventilation that needs to come in. Then, after all that, we’re putting in rails, we’re putting in the system that makes the train work. So we reach 10 years.
That’s a lot of work concentrated on a single project.
The project took the team under Wilshire Boulevard, a high-traffic area. Did this present challenges for the project?
It was definitely one of the most complex parts. When you talk about Wilshire Boulevard, you have to talk about the urban density and the construction and coordination of public services that was required to bring all these different services to the people in the area.
We’re talking sewer, electric, water, gas, telecommunications, they’re all under our corridor here, even some pipelines. We combated this with a lot of utility map verification and how we phased the work.
One of the most complex things was actually what Mother Earth gave us for tunneling. In the area we were tunneling, we had a wide variety of ground conditions. Typical of downtown LA, we had a lot of mixed floors. We had a lot of groundwater.
One strange thing about this job is that we tunneled through and built a station in the tar sands geology. You’ve probably heard of the LaBrea Tar Pits. We had a lot of potential problems with gas and ground conditions at discharge. In the reach that went through the tar sands, we had about 200 gas alerts during the mining itself, where we had to clean the machines, get everybody out, get CalOSHA approval to go back to work. So this is very different from what you would see in a typical tunnel job.
How long does this process take?
it’s fun Like everything, when it happened the first few times, we had to get out of the tunnel and get cleared by CalOSHA to go back to work. That would take hours. After the 150th time, it was a 10 minute call. We had seen this so many times before, CalOSHA allowed us to go back to work almost instantly.
In the excavation work, the team found more than 500 fossils from the Ice Age. What is it like to find them during construction?
It was during the station excavations that we found all the fossils.
We have paleontologists on site with us at all times. The first couple of discoveries were very important. As we got deeper, unless it was a new kind of animal bone, we still kept them, of course, but it wasn’t that big.
Now, I’ll tell you one of the things here at La Brea Station, we did find an almost intact mastodon skull. It was only about 15 feet deep. And because we have paleontologists on site, we actually boxed it up and used a tree box and saved all the soil and everything around the fossil and were able to transport it to our natural history museum here in town.
So what caused more delays: the fossil discovery or the CalOSHA calls?
It was definitely the CalOSHA calls, just because of the sheer number of them.
