Fort Meade, MD --
As near-peer competitors project their power into the vast expanse of the Arctic, the U.S. Air Force is positioning the world’s only fifth-generation combat-ready fighter aircraft there – the F-22 Raptor at Elmendorf Air Force Base, Alaska, and soon the F-35 Lightning II at Eielson AFB.
The DoD’s Eielson AFB regional growth plan will bring $500 million in infrastructure, including hangars, housing, maintenance facilities and simulators to prepare for an influx of the 3,500 airmen that will support the F-35 mission.
All will be built in the unforgiving environment of Interior Alaska.
Most of Alaska sits on a thick bed of frozen soil, rock and sediment called permafrost, however that permafrost is thawing.
Monica Velasco, U.S. Army Corps of Engineers’ chief of the Alaska District’s Construction Branch is responsible for the 20 construction projects for the F-35 Lightning II bed-down at Eielson AFB.
“One of the things we have on this facility, in particular, is we have permafrost. Several of our construction projects are being built on top of permafrost…there are different engineering solutions for how we deal with permafrost,” Velasco said.
In parts of Alaska, the permafrost is already starting to thaw. The heat generated by construction can cause permafrost to thaw further, damaging the new construction to the point of condemnation.
Not accounting for the amount of permafrost beneath the surface and the stability of its temperature, would spell disaster for future infrastructure. When permafrost is present, the U.S. Army Corps of Engineers has three options; thaw the permafrost, freeze the permafrost and keep it frozen, or excavate all of the soil.
Velasco explained that, you need to keep the permafrost stable or the foundation of infrastructure will eventually sink. She said the permafrost must either be thawed completely or frozen completely and kept frozen.
Before building the F-35 missile maintenance facility on Eielson AFB, civil engineers inserted pipes in a grid pattern down to the thawing permafrost over the entire build site.
Hot water is pumped through the pipes to completely thaw the permafrost layer. As the water cools, it is pumped back to the surface to be heated again. The engineers continue to monitor the ground temperature throughout the weeks making sure the permafrost is thawing evenly and completely across the site.
Once the permafrost is completely thawed, they remove the pipes and compact the soil before construction. After the building is constructed, the heat from the building will ensure the soil below doesn’t freeze again.
Sometimes thawing permafrost or excavating is too expensive, and it is more cost-effective to keep the permafrost frozen. That’s where a thermosyphon comes in.
Overlooking the rolling hills of the Tanana Valley, Alaska sits dozens of earth-covered magazines, large concrete bunkers topped with grass-covered earth, holding bullets, bombs and missiles to support the critical Arctic mission and keeping our airmen trained and ready to defend the U.S. and its allies.
For the future basing of F-35s, they needed more of these bunkers to safely store the fighter’s various modern munitions. However, deep permafrost and ice-laden soils were slowly thawing beneath the construction site, creating an unstable building foundation.
Geotechnical and civil engineers recommended a flat-loop thermosyphon system to stabilize the ground beneath the site.
According to Brian W. Schlumbohm, a F-35A technical writer/editor for the Alaska District’s U.S. Army Corps of Engineers, 25 feet below the ground, the thermosyphon structure utilizes the natural behavior of carbon dioxide gas with which it is filled.
Due to the extreme cold, temperatures of Alaska Interior winters, the CO2 gas condenses and collects on the inside of the pipes as a liquid in the above-ground, exposed portion of the thermosyphon.
The liquid CO2 then runs down to a grid of pipes, 25 feet below the surface, where it absorbs heat from the surrounding soil The extracted heat from the soil, in turn, causes the CO2 to once again turn it back into a gas, which will rise back up the thermosyphon to be cooled again. All of this occurs naturally due to the physical characteristics of thermal dynamics without the need for electricity or a motor to force the cooling.
On top of the pipe grid is a four-inch layer of foam insulation which prevents the warmer ground above from affecting the permafrost.
Using a thermosyphon system allows for a cost-effective method of maintaining a stable surface without having to change the special design of the bunkers to contain explosions that can cause a chain reaction to the other earth-covered magazines nearby.
In order to manipulate permafrost, you must first understand its properties.
The U.S. Army Corps of Engineers Engineer Research and Development Center operates the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel Research Facility near Fairbanks. The tunnels act as active laboratories, allowing scientists to monitor and study permafrost in its natural state.
“Permafrost has everything to do with living, working, and building in the sub-Arctic and Arctic region,” said Gary Larsen, operations manager at the CRREL.
Kept at a frigid 26 degrees Fahrenheit, the permafrost tunnels were dug into the side of the hill on a 16-acre parcel of land in Fox, Alaska from 1963 to 1969 for the study of permafrost, geology, ice science, and mining and construction techniques specific to permafrost environments.
Engineers originally used the tunnels to evaluate underground excavation techniques in permafrost.
It was during the excavation process that the tunnel’s’ usefulness as a natural laboratory for natural science and engineering study became apparent. The tunnel’s’ frozen walls expose a cross-section of undisturbed, constantly frozen, fossil-rich silt, sand and gravel.
Also exposed in the tunnels are ice wedges, cave ice and ice lenses. Frozen in time are bison, mammoth and horse fossils. Plant remains are still green in some places. Beatles, mites, flies, moths, butterflies and snail shells pepper the walls of the 300-foot long tunnels.
“The main research that occurred here early on was permafrost engineering. There were questions that we didn’t know, how does permafrost react to building foundations and roads…the science either helps you thaw it or refreeze it. If you have thaw-stable permafrost, which means there’s a lot of gravel in the permafrost when you thaw that out, it will stay stable forever because it will not refreeze under the current climate that we have now,” Larsen said.
The expansion of the tunnels was started in 2011 to support vital research that was limited by the smaller existing tunnels. The tunnels will be a test bed for advancing capabilities in geophysical and remote sensing standoff detection and improved engineering techniques to account for the changing state of permafrost.
The new tunnel still under excavation, 60 meters to the south of the existing tunnels, has provided more access to ice feature, and bones, and a larger view of how permafrost is changing in a warming climate.
Lt. Gen. Thomas A. Bussiere is the commander, Alaskan North American Aerospace Defense Command Region, North American Aerospace Defense Command; commander, Alaskan Command, U.S. Northern Command; commander, Eleventh Air Force, Pacific Air Forces, at Joint Base Elmendorf- Richardson, Alaska.
As the senior military officer in Alaska, He is responsible for the integration of all military activities in the Alaskan joint operations area and synchronizing the activities of more than 22,000 active duty and reserve forces from all service branches.
“The joint team in Alaska is extremely capable and professional and I have no doubt in my mind that we’ll be able to meet any challenge head on,” Bussiere said.
“The changing environment both in the Arctic and in Alaska based on climate change is providing the unique challenges, whether that’s coastal erosion or decreased permafrost. There will be challenges for the infrastructure that will have to be addressed, whether that’s along the coastline or with our installations, but I’m confident that the engineering professionals in the Air Force and the DoD would be able to address that.”