Permafrost is a common thread among soils in northern climates. Permafrost soils fluctuate seasonally as the active layer, a roughly 1 meter thick section at the ground surface thaws each summer, creating dynamic hydrologic and thermal conditions. From the fall months through spring, the active layer freezes once again, creating a continuous depth of frozen soil, which in some locations can reach hundreds of meters in depth.
Construction in northern regions presents unique challenges with respect to engineering and design in permafrost soils. For example, on Alaska’s North Slope, a relatively flat coastal plain that spans more than one hundred miles to the north of the Brooks Range, permafrost is a given and must be considered with any form of building or transportation. For instance, when designing a warehouse, drilling pad, roadway or camp, design elements will likely include a foundation elevated and insulated above the tundra that accounts for the seasonal hydrologic flux as well as potential thermal conduction that may impact underlying permafrost soils.
In many cases, flat-loop thermosyphons are built into the foundation. In Alaska, thermosyphon systems are mostly supplied by Arctic Foundations, Inc. These loops are closed and charged with a two-phase working fluid that cycles with the gradient present between the relatively warm soil and the cold atmosphere.
With observed and anticipated warming climatic conditions, added measures of passive and active foundation cooling through the use of thermosyphons are becoming more and more common as the risk and expense of damage to infrastructure and the underlying tundra becomes greater and greater. However, full risk management is not complete until the condition of the tundra and the foundation can be observed and known at any and all times. Operationally, ‘warm’ permafrost can hover a few degrees below freezing, where the margin for error is small and the risk of damage to expensive infrastructure too great.
BeadedStream LLC is an Alaska-based designer and manufacturer of customizable temperature monitoring systems that integrate with foundations built on permafrost soils. BeadedStream’s digital, multi-point Temperature Acquisition Cables (TACs) can operate independently or connect with building automation systems. These systems are designed to provide near-real time temperature data during all phases of construction and are primarily used to monitor foundations throughout the life of the building. In this way, contractors, engineers, architects and building owners can:
- Verify that building methods and design have maintained frozen soils through all construction phases, and for the life of the building.
- Monitor foundation temperatures to ensure that soil temperatures are safe; receive alerts when they are not.
- Maintain risk mitigation by having the ability to respond pro-actively to thermal changes within the foundation.
Designs that do not consider permafrost soils risk direct thermal conduction from the structure to the ground, resulting in unprecedented thaw and subsequent settlement of the foundation. In turn this can lead to damage of the structure and incur the high cost of remediation in remote arctic environments. Adding elements to the design that mitigate heat flow and allow monitoring and analysis of the building foundation temperatures are critical for successful arctic infrastructure.