Driving by the Minnesota Vikings’ massive new practice facility just off I-494 in Eagan, most people can’t help but notice the enormous Norseman-endowed, space-age metal structure rising out of the ground.
Stefan Michno, on the other hand, notices the ground—particularly, the gorgeous green natural grass practice fields that his team has had a hand in creating.
As a project manager on the KA team that is managing the construction of the new 40-acre campus, Michno is primarily focused on the outdoor stadium construction, IPF and outdoor practice fields and site work. While not as visible as the indoor practice facility itself, the practice fields are vital components, requiring a great deal of care to deliver to the Vikings’ exacting performance specifications. Michno filled us in on some of the detail that goes into the creation of the facility’s training fields.
Training Fields at TCO Performance Center
Q: How many training fields are on the site?
A: A total of six fields will be built. Two synthetic turf fields are in the enclosed 94,000 SF indoor practice facility and 6,500-seat outdoor stadium. The remaining four fields are the natural turf NFL regulation-size outdoor training fields and two of the sod fields are heated.
Q: What is the rationale for having both artificial and natural surfaces?
A: It allows players to experience the difference in playing conditions on the various surfaces where they play. The artificial turf matches the specifications of that used at their home field US Bank Stadium, and the natural sod duplicates the surfaces of other NFL stadiums.
Q: What is involved in the process of preparing the practice fields?
A: It’s a multi-step process with a lot of preparation to ensure the fields will have proper drainage. Before the sod is laid, the ground must be prepared. First, the native soil needs to be graded flat and compacted to pass a roll test. Then a drain tile system is installed about two feet under the compacted soil, along with generous amounts of pea gravel. Above that layer goes another four inches of pea gravel, which is also compacted and graded until it is as smooth as glass. Then on top of that goes a ten-inch layer of “root zone” material – comprised of 90% sand and 10 % organics. The irrigation system in the field needs to be fully operational at this time and running to wet the root zone mix and maintain proper soil compaction. Then comes the sod, which is harvested from Graff’s Turf farm in Fort Morgan, Colorado. The sod is brought in rolls inside refrigerated trucks, rolled out, and immediately maintained using fertilizers and irrigation. There are inspections at every step along the way, and it all needs to be perfect.
Q: How long does the soil preparation process take?
A: For the unheated fields, we started in the spring and installed the sod in August. Laying out the sod is a 3-week process for two fields.
Q: What about the heated fields? How are they heated?
A: The heated fields are served by an underground hydronic heating system designed and installed by Harris Mechanical. Over 62 miles of PEX piping is installed on top of the pea gravel section, spaced six inches apart across the field, delivering a 50/50 mixture of heated water and glycol at the bottom of the root zone level. Boilers located in the groundskeeper building heat the fluid mix and a series of pumps deliver the heated mix through to the fields and then back again to the boilers to be reheated and recycled back to the fields.
Q: How warm does this keep the fields?
A: The system is programmed to provide the fluid temperatures and flows necessary to achieve field surface temperatures of 32 degrees Fahrenheit, with a root zone temperature of 55 degrees while experiencing 10 to 15 MPH wind speeds at an ambient air temperature of 10 degrees.
Q: What other special care is required of the sod fields?
A: The sod requires frequent irrigation and fertilization. The irrigation piping was installed at the same time as the drainage tile and is electronically controlled by a master timer that is monitored 24 hours a day. Moisture sensors buried below the grass provide current moisture levels wirelessly to the irrigation system to keep optimal moisture level. Mowing is done several times a week during the growing season.
Q: What about the artificial turf fields? What kind of preparation do they require?
A: They are not as complex as the sod fields. We start with soil correction, compaction and grading of the indigenous substrate. Then we install the drainage system below the subgrade. A geotextile fabric is then laid on top of the subgrade to prevent the mixing of the field aggregate and native soils. Then we install flat drain tile over the geotextile fabric, an 8 inch layer of angular free draining base stone, then 2 inches of topping stone on top of that. Our new turf fields also have a new innovation, an e-layer pad just below the synthetic turf layer to cushion player impacts.
Q: What is the life expectancy of sod vs. artificial surfaces?
A: The artificial turf will last about 10 years. The natural fields will need reseeding and/or minor sod repair every year.
Completion of the TCO Performance Center is scheduled for spring 2018, adjacent to 160 acres of additional mixed-use, world-class fan- and family-friendly environment including healthcare, residential, retail, restaurant, and hotel/conference center spaces.