Business Goes Underground
At various locations in the Midwest and East, companies are converting spent limestone mines to subsurface business parks offering a host of advantages
If you're looking for a pillar of the business community in Kansas City, Missouri, think down way down -- more than 100 feet underground, to be exact, where Hunt Midwest SubTropolis has carved out the world's largest underground business complex in old limestone mines. In Kansas City and elsewhere in the U.S., engineers are working with architects, construction workers, and real estate developers to turn spent limestone mines into state-of-the-art business parks, where miles and miles of passageways stretch with gigantic pillars, painted white and numbered, serving as postal address markers.
When mining of limestone began in the late 1800s, industrialists quarried it with little regard for the shape their excavation left. By the 1950s, however, the goal had changed to that of leaving usable underground space behind. Miners carefully tunneled into hills and bluffs, removing 12-feet thicknesses of stone in grid-shaped patterns up to 150 feet below the earth's surface. Today's result: millions of square feet of space dominated by massive pillars holding up mine roofs. "The underground is a building in itself," says Dave Williams, an architect with Kansas City-based Finkle|Williams Architecture, a firm that works with SubTropolis in designing underground spaces.
The Kansas City area ranks as the leader in subsurface development with over 20 million square feet of commercial and industrial space, more than 10 percent of the total. Some 30 underground business parks populate the area, housing over 400 businesses. To give an idea of scale, SubTropolis covers 913 acres and has 6.5 miles of roads and 2.1 miles of rail corridors. It is owned and operated by Hunt Midwest Real Estate Development, which gets its name from noted industrialist Lamar Hunt, owner of the Kansas City Chiefs NFL team.
Another major player in the business is Meritex Enterprises, a real estate firm based in Minneapolis, Minnesota. Meritex has developed a complex in Lenexa, a Kansas City suburb, in recent years and also has a facility in Nashville, Tennessee.
In addition, Kentucky Underground Storage lies in Wilmore, Kentucky, about 90 miles northwest of Louisville. They store paper records, magnetic data, videotapes, and microforms and specialize in disaster recovery. W.R. Griffin founded the company and passed it on to his five daughters when he died three years ago. Its unique 30-foot ceilings -- most are 12 or 16 feet -- allow it to serve as more of a warehouse facility. Bussen Quarries, Inc., a limestone mining company, owns Bussen Underground Storage in St. Louis County, Missouri east of the city.
Underground space offers several advantages. "We don't have to deal with the elements," Williams says for starters. It provides a naturally cool, protected, and secure environment and saves on construction and energy costs. Limestone is three times stronger per square inch than concrete, allowing for storage of extremely heavy items. With disaster recovery becoming more important since the terrorist incidents of 9/11/01, companies can house computer systems underground to back up their records. In the most secure vaults at Kentucky Underground Storage, a person must go through six layers of security, plus video cameras, before entering.
But even with the advantages, engineers and others must deal with several issues unique to limestone mines to make the spaces safe and desirable. Some companies that develop and market underground parks have engineers on staff, while others bring in outside consultants, and some do a combination of both. Ventilation becomes a primary concern. Bruce reveals, "There's pretty good air flow in most mines because you usually have more than one entrance, and there's a difference in elevation."
To the uninitiated, entrances often rise up unexpectedly, and from a distance, trucks seem to disappear into the hillside. However, some facilities, such as SubTropolis, have multiple well-marked entries smack-dab in the city center. Others are more rural and may have several ways to get in and out but use one main entrance to control who comes and goes.
Varying entrance locations also contribute to fluctuations in temperatures, which typically average a constant 54 degrees F. underground. (Some underground parks hold 5K running races -- runners love the predictable, moderate temperatures). "When you have a difference in temperature from the inside to the outside of the mine, it contributes to air flow," Bruce states. Engineers use steel doors and industrial fans to stop or move the air according to each tenant's needs, he adds.
Check the Roof
Developers use different methods to ensure the rock ceilings aren't shifting. "We have bore holes we can look up into and see the strata in the roof, so we can look for laminations or loose layers," Bruce says. Engineers also use sensitive instruments equipped with warning flags developed to measure earth movement to the thousandth of an inch. "There's natural movement in the earth. If a separation begins in the stone, a flag drops down."
At Meritex Enterprises' Lenexa facility, Operations Manager Ralph Nyquist says he and his crew watch for loose rocks or any changes in the rock walls on a daily basis. Measurements are carefully checked and recorded quarterly as well.
Nyquist says air quality also ranks as important to some tenants such as those that store food products or archive records. "Every month we do air-quality checks," he says, noting particulates, radon, and carbon monoxide as items being monitored. As one way to help ensure its air quality, SubTropolis requires electric forklifts instead of the exhaust-emitting propane-powered variety.
Humidity and temperature control also present engineering and architectural challenges. "You must be able to dehumidify and bring the rooms to temperature," Bruce states, adding that records storage demands keeping humidity levels within one to two percent over the course of a year and maintaining a constant temperature.
Ironically, subsurface development has evolved as a win-win situation for limestone mine owners and subsurface developers, with each scratching the other's proverbial back. The two main supplies used to construct individual buildings in underground business parks, cement and concrete blocks, are made from limestone, and these constitute the primary uses for the sedimentary rock. "Basically, down here it's concrete floors, concrete block walls, sprinkler systems, lights, and doors and then you're in business," Nyquist quips. The irony doesn't escape Dave Williams. "They're building their buildings by digging them out," he says. But the stone's use in construction is certainly nothing new, as lime, or calcium carbonate, has been used in construction for over 3,000 years.
In the U.S. and United Kingdom, limestone is widely available and relatively inexpensive, so it is excavated and crushed for use in concrete and asphalt production and a host of other everyday uses. Many Kansas City-area buildings, roads, and highways including the runways at Kansas City International Airport were built using rock removed from the SubTropolis mine. Limestone also is used to refine sugar, manufacture glass, make paint and brown paper bags, coat chewing gum, and as an ingredient in toothpaste. Powdered limestone takes on environmental uses in neutralizing acidic lakes and rivers, soils, and gases from industrial processes.
Fire Protection Learned the Hard Way
Today's underground storage facilities operators keep close tabs on items stored there. They are suitable for light industry without chemical use, warehouse space, records storage, and offices. "We don't store anything flammable," Nyquist proclaims. If a fire were to break out, he says local fire officials would respond within about three minutes because technology in place automatically monitors the premises and alerts authorities.
Other fire protection measures are taken as well, often in combination with other functions. Portal and ventilation fans are set up to alleviate smoke or fire. Individual tenants have the ability to manually control pressurization and exhaust, and smoke corridors have been placed carefully throughout the facility. A centralized computer monitors SubTropolis' state-of-the-art fire sprinkler systems, and security officers patrol the site around the clock. At Kentucky Underground Storage, each storage vault for archival records has its own smoke and motion detectors and closed-circuit cameras. At Bussen Underground Storage in the St. Louis area, the warehouse has safety features for fire and smoke detection, carbon monoxide detection, and fresh air ventilation.
Although the former limestone mines are so massive they are, well, cavernous, those in the underground business don't like the word "cave" used in conjunction with them. "People automatically will say 'You're out in the caves.' But we like 'underground,'" Nyquist says. "This is not like the environment of a cave." Whatever you call them, underground business parks have proven a worthy alternative to the above-ground variety and even offer a few advantages. And not everybody can tell their friends or family they work underground ... in pleasant surroundings.
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