Download Permafrost Engineering

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
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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.html
http://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 Tectonics
Eastern 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:
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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 Permafrost
Use 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
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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
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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 refreezing 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 ASCE
Coduto, Foundation Design, 2nd Edition, New Jersey: Prentice Hall 2001
Solutions
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Excavation and backfill
- used to change unsuitable soils
(Fine-grained or poorly drained)
into suitable soils, like coarse
sand and gravel.
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Wooden Piles
- anchored or not anchored,
depended on the size of the active
layer.
-Should be placed well into
the permanently frozen layer and
should have a elevation of about
5 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 Foundation
http://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
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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