DART Expansion

By Larry Trojak, Trojak Communications | September 28, 2010

Provided by Terex Construction

In construction, “the right tool for the right job,” is more a directive than just a catch phrase. Contractors are continually looking for ways to make their workflow smoother, project lengths shorter and specific tasks safer and easier. Having a piece of equipment on hand that makes any — or all — of those happen can change the complexion of any project. For Dowager Construction, a subcontractor on one of the extension projects for the Dallas Area Rapid Transit (DART), the availability of a Terex® PS6000 Site Dumper, a unique, multi-use utility vehicle, turned a potentially troublesome facet of that project into an exercise in efficiency.

DARTing Out of Traffic

There’s little denying that an expansion of rapid transit in the Dallas area is sorely needed. It is reported that North Texans spend, on average, about 61 hours — better than 2-1/2 full days — of every year sitting in traffic. Meanwhile, projections for traffic volume on I-35E, the main artery into and out of the city from the north, show an increase of 45 percent by 2025. To alleviate the problem, DART has committed to building out several parts of the system throughout the city.  Archer Western is the prime contractor on the DART Green Line extension which, when complete, will add 27.7 miles and 20 stations to the system, and run from the historic Deep Ellum section of the city northward to Farmers Branch/North Carrollton. Dallas-based Dowager Construction is installing the utilities along the southeast corridor. According to Madison Smart, the firm’s Project Superintendent, the job is massive but is still only a portion of the overall light-rail expansion.

"There are also ongoing extensions to the Orange and Blue lines," he says. "All told, DART has budgeted $1.67 billion to build out several parts of this project throughout the city. It is, at least for the time being, one of the largest transportation projects in America; this section alone carries a price tag of $375 million. Studies have shown that light rail growth like we are seeing here helps create pockets of specialized developments — both commercial and residential — a real plus for the local economies. It is also believed that the expanded rail line will help join north and south Dallas, areas that have traditionally been divided by the Trinity River. There are a lot of benefits to this expansion."

Under-Track Activity

Because Dallas has literally hundreds of miles of rail lines already in place throughout the city and surrounding areas, DART has acquired rights of way on some of those existing rail lines and is building new rail for the balance. In areas in which new track is being put down, says Smart, efforts have to be made to ensure that groundwater flows away from the track bed.

"That involves installation of an underdrain system and we are doing a huge amount of that type of work on this project — more than we've ever done on a single job," he says. "In fact, by project's end, there will be better than 120,000 feet of underdrain — about 25 miles worth — in place to help draw water away from the rail bed."

The underdrain process involves placement of a layer of aggregate and, according to Smart, given limited access to some areas, that is the facet of the job in which a Terex® PS6000 Site Dumper is paying big dividends.

Tight Confines

While the overall scope of the DART project is massive in length, the work area in which Smart and his crew have to operate is generally quite narrow, creating a unique set of challenges for material movement and placement.

"In some places, the right of way may be only 65 feet to 70 feet wide," he says. "In other areas, the rail runs between ballast walls which might be only 22 feet apart or less. To complicate matters further, within this rail bed area there can be things such as catenary poles, manholes for electrical and subsystem work, and more. We have to get aggregate into these areas in advance of the underdrain and in some cases it can be next to impossible."

Perhaps the most challenging areas, according to Smart, are the newly constructed light-rail stations themselves which, depending upon the design, can either have passenger platforms on both sides or just one in the middle.

"In station areas, the rail section can be as little as 9-1/2 feet wide," he says. "What all of these different areas have in common, however, is the limited amount of work area, and because of that, the Terex PS600 Site Dumper has proven an extremely valuable tool to have around. At less than 8 feet wide, the unit is narrow enough to allow ease of movement and, because the dump bucket swivels 180 degrees, we can get right next to the ditch, turn the bed and dump the aggregate."

Best of Both Worlds

According to Walt Robertson, sales representative for Four Seasons Equipment, which is introducing the vehicles to the Dallas-Fort Worth Metroplex, the Terex PS6000 Site Dumper seems to provide two benefits that usually are self-excluding: capacity and compact size.

"Generally, you have to forsake one for the other," he says. "If you want small size you have to accept a small payload. If you want that bigger payload, you have to give up access to tighter areas. The Terex PS6000 affords contractors like Dowager the best of both worlds: a payload of better than 13,000 pounds and a nice mobile machine. For decades now, site dumpers have been very popular in Europe, due mostly to their smaller job sites. Even though our work areas here in the United States are generally larger, there are situations in which a smaller, yet still productive machine would fit the bill and we are seeing that at the DART site."

Dowager's Madison Smart agrees with Robertson. "Doing the aggregate for the underdrain could have been one of the more challenging aspects of this project. Now, we just ride alongside the ditch dumping material and we aren't hampered by tight spaces, poles, manholes, and the like. It's a perfect fit for this job and I suspect that as others use it — concrete contractors come immediately to mind — they will find it just as valuable."

Smart estimates that Dowager Construction's portion of the DART expansion project will keep them in that area for 24 to 30 months, while the overall project will be ongoing for the next five years or so.