By Capt. Christopher Edlund, LEED AP, M.SAME, USAF, and Diedrich Prigge, Ph.D.
New research is underway to analyze the climate and anthropogenic effects on the permafrost ground at Department of Defense installations in the Northern Tier. Recently, a team from the Air Force Institute of Technology (AFIT) partnered with the U.S. Army Corps of Engineers Cold Regions Research and Engineering Laboratory (CRREL) to install two long-term permafrost monitoring stations at Eielson AFB, located near Fairbanks, Alaska.
Eielson was chosen as a preferred site due to the F-35 beddown activities ongoing. With over $500 million in construction planned for the next three fiscal years, the base is a prime location to monitor how construction activities and facility operations will impact the permafrost soil in similar regions.
UNDERSTANDING THE CONCERN
Permafrost, which is the frozen soil underlying the seasonal freeze-thaw layer of soil, exists in large quantities in Alaska, Greenland, and other far north locations around the world. Since permafrost depth, extent, and moisture content vary widely, it is important to know how the substance is changing in order to help plan for future facility design in similar locations.
Building on top of permafrost poses unique challenges and must be a consideration in foundation design. It is also well documented that permafrost is changing at an accelerating rate. As a result, an inadequate understanding of permafrost soil dynamics can lead to costly facility repairs and, ultimately, mission degradation.
CRREL engineers have worked extensively to monitor the aftermath of melting permafrost at several facilities on Thule AFB, Greenland. They were able to use this experience to inform the Eielson effort.
The AFIT-CRREL team conducted two ground surveys to optimize the locations of the ground monitoring stations at Eielson. Using Electrical Resistivity Tomography (ERT), the engineers assessed two intersecting transect lines near the south loop of Eielson’s taxiway. This location will see the bulk of new construction for the F-35 beddown. The ERT results allowed the team to positively identify the existence of permafrost, and to choose two locations for monitoring changes.
After locations were established, two data loggers were placed on site. The data from the monitoring stations will show where the seasonal freeze/thaw line occurs, and whether or not the top of the permafrost soil layer is shifting.
The first monitoring station was placed directly adjacent to the south loop taxiway, in an area with a vulnerable permafrost zone. The permafrost has already experienced significant degradation due to the installation of utilities, facilities, and pavement through Eielson’s history. Planned construction of new aircraft maintenance and storage facilities will also change the way stormwater runoff is handled at the south loop.
Instead of flowing north into drainage ditches, the new taxiway design will direct stormwater into swale structures to the east of the taxiway and parking apron. The new facilities, in addition to the runoff changes, may affect the degradation rate of permafrost. The AFIT team will monitor the ground temperature at this location to quantify the anthropogenic, or “human caused,” degradation to permafrost.
Analysis of findings from Eielson may lead to a data-driven approach to be used at other remote Air Force installations across Alaska and the Arctic.
A second monitoring station was installed in a permafrost-stable area farther east. The station will serve as a control point, where permafrost changes will be primarily affected by the changes in climate over the coming years. Comparing the two stations will allow engineers to estimate the affects to permafrost caused by facilities versus the affects contributed by a changing climate.
ENSURING FIRM FOOTING
Leveraging the equipment and experience at CRREL with research interest driven by the Air Force Civil Engineer Center, AFIT hopes to emphasize the strategic opportunities for improved facility design of future facilities in the Northern Tier.
Analysis of findings from Eielson may lead to a data-driven approach to be used at other remote Air Force installations across Alaska and the Arctic. With a formula for facility construction and maintenance strategies, the possibility of a more secure north continues to improve.
Capt. Christopher Edlund, LEED AP, M.SAME, USAF, is a Graduate Student, and Diedrich Prigge, Ph.D., is Assistant Professor, Air Force Institute of Technology. They can be reached at christopher.edlund@afit.edu; and diedrich.prigge@afit.edu.
[Article first published in the November-December 2017 issue of The Military Engineer.]
