Army projects at Fort Hunter-Liggett use modular precast systems for effective, low-cost installations in remote, high-altitude locations.
Full of mountains, rivers and forests – and dotted with airstrips and live-fire ranges – U.S. Army Garrison Fort Hunter Liggett is the largest Army Reserve installation and the eighth largest in the Army. Its 165,000 acres of unencroached territory offer ideal maneuver areas for today's training needs, supporting year-round joint, multi-component, and interagency training for the Global War on Terrorism, up to Battalion Plus armored task force maneuver.
The communication installations for the base are located in a number of remote, mountaintop locations. Mission facility renovations can be costly, so a creative solution was needed to install new, state-of the-art facilities to serve the 170,000-acre coverage area for land mobile radio systems, according to Keith Gray, an engineer with 20 years of facilities experience and director of the Network Enterprise Center (NEC) at Fort Hunter Liggett.
With that in mind, Gray considered the use of durable, self-operating structures or by altering existing facilities to meet unit training and communications requirements. This avoided the costs of dealing with repairs and upgrades, and helped focus resources on training opportunities.
After researching options, Gray recommended the construction of seven small, transportable buildings in remote locations of up to 5,000 feet above sea level. Requiring enclosures as small as 12 feet by 20 feet and as large as 20 feet by 50 feet, the NEC team specified seven new structures to hold communications equipment, battery packs, solar-powered electrical service running DC systems including air-conditioning systems to protect sensitive electronics. They would also support the large antennae used to receive and relay signals, says Jon W. (Wes) Treder, with the electrical contractor Electricraft, Inc.
In order to build the complex yet small structures, Gray recommended modular precast systems that could be built off-site and trucked up the remote dirt roads by excavators. For this reason, every panel or piece of the enclosures – floors, walls and roof sections – had to weigh less than 5,000 lbs. each. "We used a model 320 hydraulic excavator, equipment trailers and bulldozers to get the sections up the mountains," says Rick Williamson, plant manager for Rockway Precast, Inc., the Las Vegas-based contractor that prepared the prefabricated buildings. "We were able to transport all of the buildings to their locations in one day."
The larger buildings were assembled from about 40 panels, all fully prewired and ducted, which took about six days to finish. The smaller buildings, which usually arrive at a site with crane access in one piece, were assembled from 11 panels in less than seven hours, says Williamson.
"We have technical requirements for our shelters, which we give to vendors, and basically left the rest up to them," says Gray. "The buildings are basically a tilt-up slab system, and the shelters had to be broken down into sections weighing under 10,000 pounds each for towing by the bulldozer, because the road's gradient was so steep."
Developed using Easi-Set pre-engineered, transportable buildings (an Easi-Set Worldwide licensed product) made of precast concrete, the shelter kits require minimal site preparation. The system did not need foundations or footings: instead, the installing team prepared a level, 6-inch layer of sand and crushed stone on a suitable sub-base for proper support and drainage.
The roof and floor panels are post-tensioned for strength and durability, while also delivering a level of airtightness and moisture control greatly exceeding that of regular precast concrete. To achieve these performance criteria, a continuous wire strand in a greased plastic sheath is incorporated in both the roof and floor at the time of casting; the strand is post-tensioned, placing the concrete in compression. This results in 40 percent more resistance to punch and shear impacts than similar, conventionally reinforced designs. The precast elements are virtually impermeable to moisture or vapor penetration without the need for roof membranes or sealers.
Easi-Set precast panel assemblies resist such challenges as wildfires, hurricane-level wind loads up to 150 mph, and earthquake shocks for Seismic Zone 4. They are also blast resistant, offering added protection for the base. Yet the prefabricated assemblies also offer basic detailing that improves the performance of the building: a turn-down roof and door guards to protect from exposure to driving rain, a raised aluminum threshold with an integral neoprene seal, and a step-down floor perimeter to prevent moisture from entering the building at floor level. While many types of finishes are available, such as brick and stucco, the buildings have a simple, exposed-aggregate look that matches the area's natural stone colors.
The logistics for the building installations was straightforward, according to the military engineering team. "As an Army training base, Fort Hunter Liggett had to shut down exercises while we were putting the buildings up," says Rockway Precast's Williamson. "We planned to execute the building program in eight weeks: one building per week, with one week off."
Using the equipment trailers and bulldozers, the panels were trucked up the dirt mountain roads and set into place by the excavator operator. In some cases, there were obstacles – such as old antenna towers and guy-wires – that required extra maneuvering. "Since 2001, our team has set a lot of buildings, but this was the first time where we had to use a track hoe rather than a crane to put the panels in place. Fortunately, the operator was phenomenally talented," says Williamson.
After the buildings were installed and checked, the electrician would take care of the interiors and finish the new communication buildings.
Best of all, the buildings provided maximum security for Army equipment while requiring minimum site preparation. They were delivered on time, set quickly and correctly, and within just a few hours the building was ready for our HVAC and electrical. For Fort Hunter Liggett, the new buildings were among the most straightforward and cost-effective projects ever undertaken on the large base.
Other recent works include four solar microgrid projects by the U.S. Army Corps of Engineers Sacramento District, one of six pilot installations selected by the U.S. Army to be net-zero energy. "The net zero initiative is going to provide energy security for this installation and it's also a priority for the Army," said Col. Donna Williams, garrison commander for Fort Hunter Liggett. Among the key reasons for the 1-megawatt installation: the susceptibility to frequent power outages at Fort Hunter Liggett, according to Bob Roy, project engineer with the Corps' Sacramento District. "That interrupts the ability to train the troops indoors and outdoors," he explains.
Similarly, the new Easi-Set building dotting the area's impressive mountainsides will ensure that there is continuity of communications capability, ensuring less downtime for one of the nation's largest and busiest training bases.
Project Facts: Fort Hunter Liggett
Buildings: 7 new buildings
Project type: Military communications support
Location: Monterrey County, California
Project challenge: Mountaintop locations with limited access
Precaster: Rockway Precast, Las Vegas
Number of panels: 11 per shelter
Panel type: Standard 10'x12'
Panel finish: Exposed aggregate
Installation period: 8 days
Manufacturer: Easi-Set Worldwide