Capture the wind

Mortenson Construction helps Orion Energy harness the wind by constructing 100 wind turbines in central Illinois. The remote location requires a close eye on logistics and a total commitment to safety.

by Clair D. Urbain

What goes around, comes around. Prairie pioneers quickly understood that if they could harness the unrelenting winds that blew across their fields, they could easily pump water and even power other mechanical marvels of the day, assuring a better life on the frontier.

In the new millennium, the same is true, but with a different twist. Instead of spindly windmills catching a breeze only 50' or 60' in the air, behemoth 125,000 lb. wind turbines are perched on 262' pedestals to convert wind into electrical energy. Increasingly, these wind turbines are sprouting up across rural counties, harvesting winds while farmers continue to harvest crops below them.

Mortenson Construction, based in Minneapolis, Minnesota, is no stranger to these types of projects. It is presently working on its 58th wind farm, installing 100 wind generators over 50 square miles in Stark and Marshall Counties in central Illinois for Orion Energy on its Camp Grove Wind Farm.

Working on a construction site that covers more than 50 square miles in rural Illinois presents some interesting logistics challenges and unique safety concerns that Mortenson crews take seriously, says David Dreis, Mortenson’s Energy Group project superintendent on the site. From concrete foundation to rotor blade, Mortenson crews plan every move for safety, quality and efficiency.

What looks simply as a column rising nearly 262' in the air is much more complicated than that. Each turbine has a complex and uniquely designed concrete base to anchor the wind turbine, provide adequate grounding for lightning protection and a way to route the harnessed electrical energy into an underground electrical grid that feeds into a substation, says Dreis.

Foundation work starts with an excavation that is a 54' or 55' square with benched walls. All are sloped as determined by soil type to provide worker safety. Each excavation has ramps for worker egress.

“The towers’ foundations are octagonal and very wide at the bottom. The depth is based on the soil conditions and some of them must be as deep as 9' and up to 50' in diameter at the base. The foundation culminates at a 17'-diameter pedestal at the ground surface,” says Dreis.

“There is a double mat of rebar. The bottom section is at the base of the foundation and the other follows the contour of the base to the surface. They also have an elaborate grounding system that is part of the foundation to help protect the wind turbine from damage caused by lightning strikes. It’s all connected to an embedded plate at the bottom of the unit,” Dreis explains.

Rebar installation
Two crews install rebar: one crew assembles the top mat and bottom mat, then a bolt cage crew places the bolts. The towers are anchored to the foundation with 140 1 7/8" bolts that run the full depth of the foundation. They are held in place at the base and top with a template and are also fixed in position to keep them centered and stable during concrete pouring.

The foundation concrete is a 5,000 or 6,000 psi mix. “We have subcontracted a batch plant and all of its trucks are dedicated to our placements. They know our traffic patterns and we get fast turnaround so the concrete gets placed fresh. We will place about 1,100 cu. yd. a day,” he says.

Once the concrete cures, another crew installs the towers and turbines. “All components come in by truck. The towers come in three pieces as a base, intermediate and top section. The nacelle and hub with blades are shipped individually, assembled onsite and then lifted into position as one unit.

“The base section is lifted into place, then the base is grouted. The intermediate section is set after the grout is placed. Once the grout has reached its design strength, the top section, turbine nacelle and rotor are installed.

“We use a Manitowoc 16000 and a Liebherr LR1400 crane for the base and intermediate section setting. We are also using the Liebherr unit on two of the most remote towers. We will set the base and midsection, then reconfigure it to set the top section, nacelle and rotor,” Dreis explains.

“On the others, we will use the Manitowoc 2250 crane for base and midsections and then use the Manitowoc 16000 to set the top tower section, nacelle and rotor. We use a triple deuce (222) Manitowoc to assemble the hub. The blades are connected to the hub on the ground.

“They can go up fast, but we can be hindered by weather. Rain without lightning is okay, but wind is our biggest challenge. The wind speed and gusts affect the crane’s load capacity, so we have to be always aware of it. We can be delayed for days because of wind. Fall and spring are unpredictable and, in the winter, it’s always windy. Summer is the best time to erect,” he says.

Moving equipment across county roads requires extensive planning. Most of these farm-to-market roads aren’t built to take these heavy loads, so Mortenson had to map every route to every site for deliveries and crane movements.

“We self-perform most of the work, but have a subcontractor handle the electrical portion. We work with two electrical contractors: one for turbine wiring and underground connection work and another for the overhead transmission line and substation work.”

Fast installation
“The conduit is prefabricated so it installs quickly. Crews can do as many as four turbines a day. The conduit comes up through the center of the foundation that provides a run outside the tower to a pad where a transformer sits. The wiring for the nacelle is also prefabricated and is already inside the tower when it is set in place. Only a small whip goes up into the nacelle.

“All wiring from the transformer to the substation is underground. The large-diameter cable that carries the power from the sites to the power grid is buried between 4' and 5' deep. The wind turbines are connected, point to point, in seven underground circuits that feed into the substation,” he says.

“M. A. (Mort) Mortenson Jr., the owner of Mortenson Construction, is unwavering about safety. He firmly believes that if you first take care of safety, quality and efficiency will follow,” Dreis says.

Every worker on any Mortenson jobsite goes through Mortenson’s orientation. It is made up of three segments: the first one, which is the longest, takes almost two hours. It is very site-specific to wind farm construction. The second and third sessions are shorter and reinforce all of the training presented in the first session. “We use a combination of classroom and hands-on training. Sessions are held on the first three weeks the worker is on the job.

“Safety is everything to us. We are a zero-injury company and we really mean zero injuries! We do everything we can to eliminate even the small risks. We start with orientation and follow up with ongoing training. We also practice empowerment. If any worker sees anything that’s an unsafe act or condition, they can stop the job and get it addressed. Most of these are taken care of by the workers or with their team members,” he says.

Jobsite stretch
Unlike most all other jobsites, Mortenson crews start the day with a 10-minute session of stretching and bending. All workers are required to do this exercise that warms up muscles and limbers up joints from head to toe. “We do this to reduce soft-tissue injuries and we haven’t had any. After all, athletes stretch before games, why not workers doing physical labor?” asks Dreis.

After the warm-up exercises, crews go through a 20-minute review of the day’s activities. “They plan their days as a team. They work through a hazard recognition card together, listing tasks to be completed and what needs to be done to do their jobs safely. They review any near misses on tasks as well and discuss them,” says Dreis, who reviews these cards daily.

“To encourage filling out the cards, we have a drawing for a $50 gift card every week. If the hazard analysis card is turned in, any worker’s name on it is eligible for that week’s drawing,” he says.

The hazard analysis card outlines how the team will do the job, forecast risks, and then plan for them. It covers every step of the task. “Just saying ‘be safe’ is not a control measure,” Dreis points out.

“I look at the cards to see if any trends are developing. The cards cover tool inspections, equipment problems, or whether special permits that are needed had been obtained, to name a few. Each team identifies and works through the hazards.

“The cards don’t have to be in perfect English or have perfect spelling, but we do want them to be thought out. Typically, we review 25 or 30 cards a week. They note on the card whether they or the work team corrected the issue or if it’s something I need to get involved with,” he says.

With the variety of tasks taking place, several work crews are spread out over the 50 sq.-mile jobsite. “We have several types of work crews and they change as the job changes. We have excavation, foundation, offload, clean tower, set base/midsection, build rotor, main erection, crane walkers and final grade crews. We also have two-man de-watering crews because we routinely encounter groundwater. We always send at least two guys out per site and each site has at least one radio. No one works alone,” he says.

Mortenson has a first responder system in place. “We have not used it for a company emergency, but we have used it with two local accidents and with one delivery person who thought he was having a heart attack. In all cases, we had medics on the site within 11 minutes from towns that are five or six miles from the site. We have planned for this and set up traffic control. We work closely with local first responders so they know what to expect and where to go. As the job progresses, we conduct mock runs that test our first responder system. Our first one focused on carpenter/laborers, then we conducted another for millwrights and iron workers. As the trades change on the job, we modify the mock run to test the response that would be needed for the type of accident that may occur with that trade,” he says.

Operational in 2008
The crews broke ground in early 2007 and plans are in place to have the turbines producing enough electricity to power up to 45,000 homes by early 2008. The sophisticated units each produce up to 1.5 MW, turning with only 8 or 9 mph winds. The turbines’ blades rotate in the hub to take best advantage of the wind speed. The units will shut off at wind speeds greater than 35 or 40 mph.

With proper planning and commitment to safety, the early-2008 power-up date is definitely achievable.

Click here to see more images of tower construction at the site.

Published in the November/December 2007 issue of Contractor Tools and Supplies magazine.

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David Dreis, Mortenson Energy Group project superintendent at the Camp Grove Wind Farm, works closely with his crew and subcontractors to achieve a zero-injury company. Crews are setting 100 wind turbines across 50 square miles of Illinois farm fields.

About the size of a small motor home, this encell (turbine) is ready to be placed on top of the tower.

Blades are moved and bolted into place onto the rotor. There is enough room inside the rotor for a man to work. The blade frame is steel and the shell is fiberglass.

The electrical connections that carry energy from the turbine encell to the transformer outside of the tower snap together for a tight fit. Each windmill is made up of a three-section tower, encell, hub and rotors.

Crews power wash every component before it’s lifted into place. Here, a top section of the tower gets scrubbed down before the pick.

Mortenson work crews stretch every morning before the day’s safety and work briefing. Goal: eliminate soft tissue injuries.