Permafrost Engineering in Alaska

By Don Reid, Adam Price, Sabine Eisma, Casey Wagner and Logan Wallace

Permafrost Engineering in Alaska

•Basic Alaskan Geography and Geology

•Permafrost features and distribution

•Permafrost Engineering Attributes

•Foundations in Permafrost

•Water Prospecting in Frozen Soils

Alaskan Geology

• Formation of Alaska

• Ice Age

• Seismic Activity

• Ice Fields

• Mountains and Minerals

• Aleutian Mountain Chain

http://www.alaskadenalitours.com/alaska_natural_history/alaska_geology.html

Formation

• Alaska formed ~125 million years ago

• Two hypotheses on formation– Merging of 7 plates

– Formed From Merger of Pacific and N. American Plates

http://www.alaskadenalitours.com/alaska_natural_history/alaska_geology.html

Cold Past

• Pleistocene Ice Age– 2.5 mya – 9 kya

– Alaska connected to Asia by landbridge due to lowered sea level (el. -350 feet)

http://www.alaskadenalitours.com/alaska_natural_history/alaska_geology.htmlhttp://www.alaskageography.com/essays/geology.htm

Seismic Activity

• ~4% of all energy released by earthquakes has Alaskan origin.

• Caused by the Pacific Oceanic plate slipping under the North American Continental plate

• Mostly focused around south central Alaska

ttp://geology.com/novarupta/

Ring of Fire

http://www.usgs.gov/

Alaskan TectonicsEastern Segment

Central Segment

http://3rdrock.gly.uga.edu/petrology/redoubt/plates.gif

Ice Fields

• Land areas completely covered in ice, year round.

• Cover 28,80 square miles

• 4.9% of Alaska

ttp://www.usgs.gov/global_change/glaciers/default.asp

Mountains and Islands

• 20% of Alaska’s land area is over 4,500 feet above sea level

• Mountain ranges split Alaska into 5 sections:– The Interior– The Arctic– The Aleutian Islands– Southeast Alaska– South-central Alaska

• Alaska is rich in minerals• Some of the many minerals deposits found in Alaska:

Gold, copper, silver, mercury, platinum, tin, coal.

http://www.alaskageography.com/essays/geology.htm

Aleutian Islands

• In the Ring of Fire

• Highly active - 26 of the 57 Volcanoes have erupted since 1970

• Volcanic arc is fed from the subduction of the Pacific plate sinking beneath the North American plate

• No trees and little to no vegetation

http://www.alaskageography.com/essays/geology.htm

Permafrost

• Definition: Ground that has been continuously below the freezing point of water for two successive winters and the intervening summer

• Below layer of “active” sporadically frozen soil.

http://gsc.nrcan.gc.ca/permafrost/whatis_e.php

http://www.wunderground.com/climate/permafrost.asp

Permafrost Formation

• Earth has a fairly constant temperature gradient (approximately 3 degrees Celsius per 100 meters).

• As surface temperatures go below freezing, permafrost can form to varying depths.

http://www.uspermafrost.org/

http://gsc.nrcan.gc.ca/permafrost/whatis_e.php

Distribution of Permafrost

• Generally continuous north of Fairbanks and discontinuous in southern portions of Alaska.

https://uascentral.uas.alaska.edu/online/ALST300-JD1/homesite?term=Spring-2009;behavior=UAS

Surface Formations

• “Patterned Ground” - A phenomenon on the active layer caused by freeze/thaw cycles. Freeze cycles churn and sort finer grain soils to the surface.

http://www.physicalgeography.net/fundamentals/10ag.html

Surface Formations

• Pingos – Frozen subsurface lake surrounded by permafrost. The density of the permafrost does not give way, forcing the expanding ice up, creating a blister like formation beneath the active layer.

http://www.uspermafrost.org/

Pingo

http://www.aktrekking.com/Brooks.html

Mechanical Properties of Permafrost

http://www.wunderground.com/wximage/viewsingleimage.html?mode=singleimage&handle=akalaska&number=15

Characterization of PermafrostUse soil grain characteristics, crystalline structure of ice, temperature ratio of interstitial ice to soil grains to determine mechanical properties

Source: Nelson et al, “Cold Regions Engineering.” U. of Wash. 2008

Elastic Modulus

• Vary Widely, but higher in frozen soils

• Brittle, stiff, “rocklike.”

• Wave speed is greater (stress waves and seismic waves)

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Strength

• Ice Poor Soils– Dominated by coarse grained or dense fine-grained

soils – Generally, strength is about the same as un-frozen

soils (Can be slightly lower): τ = cf + σn tanϕ

• Ice Rich Soils– Dominated by loose fine-grained soils– Bulk Density under 1000 kg/m3

– Strength dominated by cohesion of interstitial ice– τ = cf + σn tanϕf

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Basic Effect

Source: Nelson et al, “Cold Regions Engineering.” U. of Wash. 2008

Creep

• “Slow progressive movement of a loaded frozen soil without volume change.” (Smith, p 3-33)

• Slow liquid movement• Short term (Primary) Creep: Strain Rate starts

high, decreases.• Secondary Creep: Long term, low. Constant

strain rate.• Tertiary Creep: Accelerating Strain Rate. Can

be short. Soil is considered to have failed.Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Sample Issues with Permafrost

• Frost Heaving– The freeze cycle of the active layer presses against the

permafrost layer, forcing the freezing soil to expand upward.

• Thawing– Building constructed on permafrost can offset the

thermal balance causing thawing of the permafrost layer. Permafrost thawing results in settling, undermining foundations and structures.

• Excavation Difficulties

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Excavation Difficulties

• Permafrost excavation is similar to that of intact rock masses.

• Typical soil excavation techniques are inadequate

• Some permafrost excavation options– Heated water bladders thaw the soil before excavation

– Steam jets

– Explosives

– Jackhammers

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

http://en.wikipedia.org/wiki/Permafrost

Permafrost and Foundations

Rice, Building in the North, 4th Edition, Anchorage: Alaska Science & Technology Foundation

Frequent Foundation Problems

• Up-heave caused by cyclic thawing and re-freezing of soils.

• Thawing of soils around foundation is caused by either heat leaking from the foundation or by seasonally varying temperatures.

• Frost-Jacking: Poles/piles become unstable when bottom few feet is not placed in permanently frozen soil.

Andersland and Ladanyi (1994), Frozen Ground Engineering, 2nd Edition, John Wiley and Sons, Inc. for ASCECoduto, Foundation Design, 2nd Edition, New Jersey: Prentice Hall 2001

Solutions• Excavation and backfill

- used to change unsuitable soils(Fine-grained or poorly drained)into suitable soils, like coarse sand and gravel.

• Wooden Piles- anchored or not anchored,depended on the size of the activelayer. -Should be placed well intothe permanently frozen layer andshould have a elevation of about5 feet above ground level.-Should be wrapped in a “low friction” plastic sleeve covering the depth of the active layer to prevent frost jacking

Rice, Building in the North, 4th Edition, Anchorage: Alaska Science & Technology Foundationhttp://www.letmecolor.com/wp-content/uploads/2008/05/hydraulic_excavator_coloring_page_12133.gif

Foundation Temperature Control

To prevent thaw/freeze problems, soils around foundation are kept cold by

° Ventilation

° Mechanical Refrigeration

° Insulation

Rice, Building in the North, 4th Edition, Anchorage: Alaska Science & Technology Foundation

More Solutions…

• Post and Pad Footing - mostly used by people who build their own homes. Easy to build, cheap and easy adjustable.

Rice, Building in the North, 4th Edition, Anchorage: Alaska Science & Technology Foundation

Permafrost and Water Supply in Alaska's North

• Alaska has an abundance of surface water sources such as lakes and rivers. The run- off rates are very high along the Pacific coast, dropping off significantly in the central and northern parts of the state. In the north, rivers and lakes freeze to their full depth in winter so are not practical water sources.

• 83% of Anchorage public water supply is from surface water.

• 100% of Fairbanks public water supply is from ground water. (USGS Alaska Annual Data Report 2005)

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Groundwater in Permafrost

• A. Suprapermafrost - Water above the permafrost (in the active layer). In the Arctic region, the active layer is 1~6 feet. Very little water accumulates in this layer, and what does is often contaminated and is frozen in winter.

• B. Intrapermafrost- Water within the permafrost layer- In order to stay in the liquid phase, water within permafrost layers must have high concentrations of dissolved solids. The water pockets are constantly changing and there is, as yet, no economically feasible way to access this source.

• C. Subpermafrost- Water below the permafrost layer. This is the most dependable place to find high quality water in large quantities. In general, the deeper the source, the warmer the water will be and therefore the least likely to freeze during extraction.

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

Groundwater in Permafrost

http://www.amap.no/mapsgraphics/go/search/q/%22Terrestrial%20environment%22%20OR%20%22permafrost%22

Subpermafrost Water• Alluvial- below very thick alluvial deposits where the permafrost layer is

not too thick. • Layered- Stratified bedrock may have water filled layers (aquifers) that

have considerable yield. Wells should be situated along the axis of a syncline and the deepest, warmest one is likely to be the most productive.

• Fissured- Subpermafrost water in joints caused by tectonic forces or weathering. Joints caused by tectonics are quite deep and are rare in Northern Alaska. Those caused by weathering are much more common and can contain significant quantities of water. They are generally a lot shallower and therefore may be frozen in winter in areas where the permafrost is thin.

• Solution Channels- Found in areas of high limestone content. Also known as Karst water, it is found in the cavities in eroded carbonate bedrock In Northern Alaska, karst landscapes exist in the Brooks Mountains and the White Mountains.

Source: Muller, Siemon W. ,"Frozen in Time” ASCE 2008

Other Water Sources

• Very deep lakes are plumbed in winter and the water stored in heated tanks.

• In small, remote settlements in the far north, such as Arctic islands, glacier and river ice is used as the only source of water.

Source: Smith, D.W. Ed “Cold Regions Utilities Monograph” ASCE, 1996.

End

http://www.fbuzz.com/pgallery/v/nature/lakes/ColdMountainLakeAtDusk-Skarstad-Norway.jpg.html