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Mount Commonly Used |
Stability |
Cost |
Install Time |
Labor |
Substrate |
Site Impact |
 |
 SCIGN mount |
 med-high |
 $6,700-16,000 |
 1-4 d |
 1 |
U |
high |
The geodetic thermopile monument allows installation of high-precision GPS/GNSS instruments for measuring tectonic signals in areas characterized by permafrost. The monument was designed for EarthScope’s Plate Boundary Observatory (PBO) and has been installed at three sites in northern Alaska (AB18, AB45, and AB46). The monument consists of a single 4" (4.5" OD), 20’-long pillar containing pressurized, two-phase carbon dioxide to prevent thawing at the monument’s base; this pile is set ~16’ deep into the ground and coupled to the permafrost with a slurry of sand and water, which freezes in 1-10 days after installation. The portion of the monument in the active surface layer is wrapped in insulation to prevent deformation of the monument due to freeze-thaw activity; this portion of the hole is back-filled with soils saved from the drilling. Thermopile-monumented PBO sites AB45 and AB46 show reasonable multi-year stability.
Check out PBO Installs First of Four Permafrost GPS Stations in Alaska.
Site AB18 of EarthScope’s Plate Boundary Observatory (PBO).
Pros
can be installed in permafrost
Cons
labor and tool intensive (requires a drilling rig and crew)
expensive (can be $6,700 to $16,000, depending on drilling)
can be time intensive (requires 1-4 days)
may not be able to install in some remote locations... depends upon ease of site access
large construction disturbance footprint
Design and Construction
A drilling contractor is required to install this monument.
Documents
Final thermopile design report from Duane Miller Associates LLC in .pdf format:
Thermopile fabrication diagram from Arctic Foundations, Inc. in .pdf format:
Installation Photos
An oversized vertical hole is drilled approximately 18 feet into the substrate.
The 20’-long pile is lowered into the hole.
The pile is set into the permafrost with potable water or a mix of water and sand.
Approximate Cost
$6,700-16,000 total, depending principally on drilling (distance and mode by which drill rig needs to travel to and from the site). Monument cost is $1700, drilling costs have ranged from $5,000 to $14,000 depending on whether there was a local drill rig available vs. needing to e.g. ship a drill rig to the site by cargo aircraft.
This cost is for the monumentation only; the antenna mount (e.g. SCIGN mount) is not included.
Materials
thermopile
10-mil visqueen (polyethylene wrap) to wrap the top 4.0-5.0’ buried portion of thermopile
water (provided by drillers
threaded adapter (if using SCIGN mount)
Tools
drill rig capable of drilling a 6.0"-diameter boring
hoist or boom truck for lowering thermopile into boring
shovels for backfill around thermopile
level
pipe wrench
compass
tape measure
Mount Commonly Used
The SCIGN mount is the antenna mount used to date with the thermopile monument, although it is only required when using the SCIGN radome. Otherwise, any other leveling mount, such as the SECO 2072-series antenna mount, is acceptable.
Send questions or comments to Support (support
unavco.org).