Appendix_R_-_FY13_Dormitory_Permafrost_ _Geotechnical_Investigation.pdf

Addendum II Thule Air Base

FY13 Dormitory Permafrost and Geotechnical Investigation

August 13, 2012

ERDC-CRREL

Approved for public release; unlimited distribution

Addendum II

FY13 Dormitory Permafrost and Geotechnical Investigation

Kevin Bjella, MSc., P.E.

Cold Regions Research and Engineering Laboratory - CRREL

Engineer Research and Development Center – ERDC

U.S. Army Corps of Engineers - USACE

Building 4070, Fort Wainwright, Alaska 99703

August 13, 2012

Prepared for:

New York District

Army Corps of Engineers

US Army Corps of Engineers ®

US Army Cold Regions Research and Engineering

Preface

This report and field work were completed by Kevin Bjella, Research Civil Engineer, U.S. Army Cold Regions Research and Engineering Laboratory (CRREL), and performed under MIPR #W16ROE-1069- 3123.

The author gratefully acknowledges the assistance of Dr. Edel Cortez (CRREL) for his review of this report, and Marc Beede (CRREL) for his valuable field assistance. The author would also like to thank Greenland Contractors personnel for their support during the field work of this project.

For more information contact:

Kevin Bjella 907-361-5171 kevin.bjella@us.army.mil

This report reflects the personal views of the author and does not suggest or reflect the policy, practices, programs, or doctrine of the U.S. Army or the Government of the United States. The contents of this report are not to be used for advertising or promotional purposes. Citation of brand names does not constitute an official endorsement or approval of the use of such commercial products.

Figure 1. Borehole locations around Bldg. 101. and temperature measurement location across

Crescent Road to the south.

Grid 2

N

BH-4

BH-2

BH-3

BH-1

Soil Temperature Measurement Location

1. CONCLUSIONS AND RECOMMENDATIONS

The subgrade soils below the active layer and down to 5.0-m to 6.0-m are extremely ice-rich. A conventionally constructed, at-grade heated structure, with any type of foundation, would transfer an adverse amount of heat energy into the soil, causing considerable differential thaw-settlement. Most recent MILCON projects at Thule (Medical Bldg., FY05 Dorm, FY12 Dorm) have utilized pre-cast concrete footer and column foundations. The footer is buried below the bottom level of the active layer, and this provides a continuously frozen embedment for the footer and the bottom of the column. This foundation technique is expensive due to the cost to excavate over 2.0-m of hard frozen glacial till and gravel, which must be done under the entire structure.

Placed steel pipe pile foundations are also an alternative. The holes for pile installation would be spot drilled with the appropriate sized drilling rig, and the piles are then backfilled with a sand slurry mixture.

Because bedrock is inferred to exist at a relatively shallow depth, from approximately 5.5-m to 8.0-m across the site, drilling will most likely encounter this bedrock within a feasible distance to install an adfreeze/end bearing piles that do not solely rely on frozen ground for bearing capacity. Alternatively, if competent bedrock is not encountered within a feasible depth, an adfreeze pile can be installed. The

Adfreeze pile obtains the load carrying ability through the adfreeze bond between the hole annulus and the pile surface.

Both the pile and column/footer designs elevate the structure above grade, and they have a few advantages when placed on ice-rich permafrost. Firstly, they allow for elevation of the structure above grade, providing air circulation between the bottom of the first floor and the surface, and this significantly decreases or eliminates the amount of heat transfer from the building to the foundation soils. Secondly, this requires that the superstructure, which transfers the load from the building to the posts, be designed to withstand differential settlement in a more robust manner than with a continuous footing type foundation.

Additionally, in the event of minor thaw settlement, they also provide access for re-leveling.

One disadvantage to the adfreeze-only pile foundation, and the footer and column foundation, is the uncertainty of climate change. How conservative should the design be to insure longevity with warming permafrost and deepening active layer?

1.1 Alternative I – Buried Footer and Column Foundation

The general construction method should insure that the foundation footers are placed in such a manner within the compacted fill pad that the permafrost table is absolutely protected from thaw conditions and is assured to refreeze to above the footer, at least one to two footer thickness (tf). This insures that the footer will never be impacted by destructive freeze-thaw cycling, and weakening of the load bearing compacted fill. Placement of rigid board insulation provides thermal resistance, insuring a maximum depth of thaw to above the footers (Figure 2). The following design is recommended with alternatives:

• Excavation and discard of the active layer soils. This requires a minimum of 1.5-m to 1.8-m of soils to be removed below the surface.

• After the active layer soils have been removed, visual observations are required to insure that none of the specific locations where footers will be placed consist of massive ice (wedge ice or relict ice). If massive ice is located within the footprint of the footer, over-excavation and complete removal of this ice is required before select fill placement. This will eliminate the destructive effects of creep settlement of the massive ice.

• Placement and compaction of NSF select material (< 3% fines passing 0.02 mm) to at least two footer thicknesses on the top of the permafrost, compacted to 95% optimum density (ASTM

D1557 Modified Proctor), and should extend beyond the perimeter of the structure by 2.5Lf.

• Placement of the footers.

• A thickness of NFS material should then be placed and compacted to 95% optimum density

(D1557), from the bottom of the footer, to a minimum twice the footer thickness above the footer.

The fill will extend beyond the perimeter of the structure a minimum of 2.5Lf.

• Rigid board polystyrene insulation should then be carefully placed together under the entire structure at a minimum depth of 0.6-m below final grade, and extending beyond the perimeter a minimum of 2.0Lf. The insulation shall be two layers of 5cm thick XPS insulation butt together and overlapped.

• Continue placement with NSF material compacted 90% optimum density (D1557) to the final grade, insuring that the rigid board insulation does not shift during placement. Final thickness of compacted fill above insulation shall be a minimum of 0.6m. This fill will extend beyond the perimeter of the structure a minimum of 2.5Lf.

• The columns extending from the structure to the footer should be insulated, and thermally decoupled from the structure if possible to prevent thermal bridging.

*The following excavation depths and replacement thicknesses assume the pre-construction grade is equal to the final grade. Because this project site is slightly sloping, care must be taken to insure that all active layer soils are removed, regardless of the elevation of the final grade.

Figure 2. Alternative II general foundation plan. Not to scale.

A previous geotechnical investigation for the FY05 Dormitory, within 60-m of this project site, reported that the Standard Penetration Tests (SPT) (ASTM 1586) produced blow counts (N values) in excess of 100 per 15.2cm for 27 of 31 intervals tested in five boreholes. Seven of the intervals required greater than 120 blows per 15.2cm, and four of the intervals required 200 blows per 15.2cm (Baker, 2004). The blow counts indicate the instantaneous strength of these soils is extremely high, and this would be expected from large particle size sediments such as gravels and larger, cemented in an icy matrix. However, the moisture contents indicate thick intervals of sediments containing excess ice.

Mechanically, this indicates many of the soil particles are not in contact, therefore long term loading will deform the ice and particles visco-elastically. Therefore the design of the foundation on ice-rich soils should be governed by long term strength. The long term strength of ice-rich soils is a function of time and temperature, and the maximum temperature expected at the ice-rich soil and NFS fill interface was calculated to be -2.2°C utilizing the Modified Berggren equation and also TEMP/W two-dimensional soil temperature modeling software.

Laboratory measurement of short term and long term strength is a time consuming process, and requires the delivery of intact frozen samples to the laboratory. Therefore it was determined to omit those tests. A conservative empirical estimation often used in-lieu of laboratory data is given by Johnston

(1981). This estimation is based on compilation of data from ice-rich soils and from investigators, both

North American and Russian. It can be seen that the long term strength is a function of the temperature of the ice-rich soils:

σf = 35 + 28(0-Ts) (kpa) (4.2) where:

σf = long term (50 year) shear strength

0-Ts = the temperature at the critical depth (always positive)

By assuming the shear strength is near zero due to the ice content, Terzaghi’s equation for shallow square foundations can be reduced to:

..FS

q fc f σ = (4.3) qf = bearing capacity of the soil (kpa)

Nfc = 5.14 is a shape factor for circular or square foundations σ = long term shear strength of the soil

S.F. = is the factor of safety

For a calculated maximum temperature at the permafrost fill interface of -2.2°C, and a factor of safety of 3.0, we obtain an allowable bearing capacity of 165 kpa. This solution does not specifically determine the amount of settlement that will occur, however, because the footers will be placed on a thick layer of compacted fill, the ultimate load that is transferred from the fill to the permafrost should not exceed the above value, it is our opinion that creep settlement will be negligible and within normal tolerances for foundation such as this.

1.2 Earth Work

1.2.1. Alternative I – Footer and Column Foundation.

The earthwork for the footer and column foundation will require that the active layer soils should be removed and not re-used as structural fill material. This will equate to a minimum 1.5-m to 1.8-m thickness across the entire site and should extend beyond the perimeter of the building by 2.5Lf, where Lf is the largest horizontal dimension of the footer. These active layer soils are non-consolidated and contain a percentage of fines that exceed the maximum value of 3% (Baker, 1984), which classifies them as frost susceptible soils. If they are to be used, it should only be for non-structural fill applications, and preferably not within 2.0-m of the structure at any location.

It is assumed that footers and columns will arrive as soon as possible via ocean going vessel, which probably cannot occur until sea ice conditions allow in late June, or if icebreaking of the channel occurs.

Excavation of the active layer soils can take place any time prior to the arrival of the footers and columns, however, extreme care should be taken to not allow for thaw of the design elevation of the permafrost/fill interface. It is recommended that excavation proceed to approximately 0.5-m above the design permafrost/fill interface until the foundation materials have arrived or are about to arrive. It is also recommended that a CRREL representative be available during the excavation to ascertain the areas requiring over-excavation of massive ice (wedge or relict ice).

All the fill material shall be clean, select fill gravel allowing for dense compaction, and possessing no more than 4% fines. The fill will extend beyond the perimeter of the building as noted above and may be gradually sloped away from the building at 2:1 horizontal to vertical. Positive drainage away from the perimeter of the building preventing surface flow beneath the structure is required. Care should be taken to insure that no down-wind topographic lows occur that may allow for accumulation of drifted snow which will not be removed under normal snow removal procedures. The accumulated snow will serve as a very efficient thermal insulator, and winter heat extraction will be reduced in those areas allowing for diminished temperature decrease in the subsurface.

1.3 Long Term Temperature Monitoring

For structures located on permafrost, long term temperature monitoring is important for analyzing the performance of the foundation system and aid future engineering decisions. It is recommended that for either foundation alternative, a minimum of six thermistor strings be installed from the surface down to an appropriate depth. For Alternative I, vertical installation of 2.5cm diameter PVC pipe, shall be completed by drilling after the compaction of the fill material. The joints of the PVC pipe will be cemented and capped on the bottom for water tightness. The thermistor strings are then inserted into the

PVC.

For adfreeze pile foundations, at least two strings should be located down the entire length of the pile, while the other four may be obtain a shallower depth and be located away from the piles. For the footer and column foundation, all the strings should extend down to the bottom of the excavation, with some located near the columns, and some located away. When a final decision is made regarding the foundation type, the temperature monitoring design can be determined.

Addendum I

May 5, 2012

ERDC-CRREL

Addendum

FY13 Dormitory Permafrost and Geotechnical Investigation

Kevin Bjella, MSc., P.E.

Cold Regions Research and Engineering Laboratory - CRREL

Engineer Research and Development Center – ERDC

May 5, 2012

Regions Research and Engineering Laboratory (CRREL), and performed under MIPR #W16ROE-1069- 3123.

The author gratefully acknowledges the assistance of Dr. Edel Cortez (CRREL) for his review of this report, and Marc Beede (CRREL) for his valuable field assistance. The author would also like to thank Greenland Contractors personnel for their support during the field work of this project.

For more information contact:

Kevin Bjella

This report reflects the personal views of the author and does not suggest or reflect the policy, practices, Figure 1. Borehole locations around Bldg. 101. and temperature measurement location across

Crescent Road to the south.

Soil Temperature Measurement Location

1. CONCLUSIONS AND RECOMMENDATIONS

conventionally constructed, at-grade heated structure, with any type of foundation, would transfer an adverse amount of heat energy into the soil, causing considerable differential thaw-settlement. Most recent MILCON projects at Thule (Medical Bldg., FY05 Dorm, FY12 Dorm) have utilized pre-cast concrete footer and column foundations. The footer is buried below the bottom level of the active layer, and this provides a continuously frozen embedment for the footer and the bottom of the column. This foundation technique is expensive due to the cost to excavate over 2.0-m of hard frozen glacial till and gravel, which must be done under the entire structure.

Placed steel pipe pile foundations are also an alternative. The holes for pile installation would be spot drilled with the appropriate sized drilling rig, and the piles are then backfilled with a sand slurry mixture.

Because bedrock is inferred to exist at a relatively shallow depth, from approximately 5.5-m to 8.0-m across the site, drilling will most likely encounter this bedrock within a feasible distance to install an adfreeze/end bearing piles that do not solely rely on frozen ground for bearing capacity. Alternatively, if competent bedrock is not encountered within a feasible depth, an adfreeze pile can be installed. The

Adfreeze pile obtains the load carrying ability through the adfreeze bond between the hole annulus and the pile surface.

Both the pile and column/footer designs elevate the structure above grade, and they have a few advantages when placed on ice-rich permafrost. Firstly, they allow for elevation of the structure above grade, providing air circulation between the bottom of the first floor and the surface, and this significantly decreases or eliminates the amount of heat transfer from the building to the foundation soils. Secondly, this requires that the superstructure, which transfers the load from the building to the posts, be designed to withstand differential settlement in a more robust manner than with a continuous footing type foundation.

Additionally, in the event of minor thaw settlement, they also provide access for re-leveling.

One disadvantage to the adfreeze-only pile foundation, and the footer and column foundation, is the uncertainty of climate change. How conservative should the design be to insure longevity with warming permafrost and deepening active layer?

1.1 Alternative I – Buried Footer and Column Foundation

The general construction method should insure that the foundation footers are placed in such a manner within the compacted fill pad that the permafrost table is absolutely protected from thaw conditions and is assured to refreeze to above the footer, at least one to two footer thickness (tf). This insures that the footer will never be impacted by destructive freeze-thaw cycling, and weakening of the load bearing compacted fill. Placement of rigid board insulation provides thermal resistance, insuring a maximum depth of thaw to above the footers (Figure 2). The following design is recommended with alternatives:

• Excavation and discard of the active layer soils. This requires a minimum of 1.5-m to 1.8-m of soils to be removed below the surface.

• After the active layer soils have been removed, visual observations are required to insure that none of the specific locations where footers will be placed consist of massive ice (wedge ice or relict ice). If massive ice is located within the footprint of the footer, over-excavation and complete removal of this ice is required before select fill placement. This will eliminate the destructive effects of creep settlement of the massive ice.

• Placement and compaction of NSF select material (< 3% fines passing 0.02 mm) to at least two footer thicknesses on the top of the permafrost, compacted to 100% optimum density (ASTM

D1557 Modified Proctor), and should extend beyond the perimeter of the structure by 2.5Lf.

• Placement of the footers.

• A thickness of NFS material should then be placed and compacted to 95% optimum density

(D1557), from the bottom of the footer, to a minimum twice the footer thickness above the footer.

The fill will extend beyond the perimeter of the structure a minimum of 2.5Lf.

• Rigid board polystyrene insulation should then be carefully placed together under the entire structure at a minimum depth of 0.6-m below final grade, and extending beyond the perimeter a minimum of 2.0Lf. The insulation shall be two layers of 5cm thick XPS insulation, butt together and overlapped.

• Continue placement with NSF material compacted 90% optimum density (D1557) to the final grade, insuring that the rigid board insulation does not shift during placement. Final thickness of compacted fill above insulation shall be a minimum of 0.6m. This fill will extend beyond the perimeter of the structure a minimum of 2.5Lf.

*The following excavation depths and replacement thicknesses assume the pre-construction grade is equal to the final grade. Because this project site is slightly sloping, care must be taken to insure that all active

Figure 2. Alternative I general foundation plan. Not to scale.

reported that the Standard Penetration Tests (SPT) (ASTM 1586) produced blow counts (N values) in excess of 100 per 15.2cm for 27 of 31 intervals tested in five boreholes. Seven of the intervals required greater than 120 blows per 15.2cm, and four of the intervals required 200 blows per 15.2cm (Baker, 2004). The blow counts indicate the instantaneous strength of these soils is extremely high, and this would be expected from large particle size sediments such as gravels and larger, cemented in an icy matrix. However, the moisture contents indicate thick intervals of sediments containing excess ice.

Mechanically, this indicates many of the soil particles are not in contact, therefore long term loading will deform the ice and particles visco-elastically. Therefore the design of the foundation on ice-rich soils should be governed by long term strength. The long term strength of ice-rich soils is a function of time and temperature, and the maximum temperature expected at the ice-rich soil and NFS fill interface was calculated to be -2.2°C utilizing the Modified Berggren equation and also TEMP/W two-dimensional soil

Laboratory measurement of short term and long term strength is a time consuming process, and requires the delivery of intact frozen samples to the laboratory. Therefore it was determined to omit those tests. A conservative empirical estimation often used in-lieu of laboratory data is given by Johnston

(1981). This estimation is based on compilation of data from ice-rich soils and from investigators, both

North American and Russian. It can be seen that the long term strength is a function of the temperature of

By assuming the shear strength is near zero due to the ice content, Terzaghi’s equation for shallow square q fc f

Nfc = 5.14 is a shape factor for circular or square foundations safety of 3.0, we obtain an allowable bearing capacity of 165 kpa. This solution does not specifically determine the amount of settlement that will occur, however, because the footers will be placed on a thick layer of compacted fill, the ultimate load that is transferred from the fill to the permafrost should not

1.2 Earth Work

1.2.1. Alternative I – Footer and Column Foundation.

The earthwork for the footer and column foundation will require that the active layer soils should be removed and not re-used as structural fill material. This will equate to a minimum 1.5-m to 1.8-m thickness across the entire site and should extend beyond the perimeter of the building by 2.5Lf, where Lf is the largest horizontal dimension of the footer. These active layer soils are non-consolidated and contain a percentage of fines that exceed the maximum value of 3% (Baker, 1984), which classifies them as frost susceptible soils. If they are to be used, it should only be for non-structural fill applications, and preferably not within 2.0-m of the structure at any location.

It is assumed that footers and columns will arrive as soon as possible via ocean going vessel, which probably cannot occur until sea ice conditions allow in late June, or if icebreaking of the channel occurs.

Excavation of the active layer soils can take place any time prior to the arrival of the footers and columns, however, extreme care should be taken to not allow for thaw of the design elevation of the permafrost/fill interface. It is recommended that excavation proceed to approximately 0.5-m above the design permafrost/fill interface until the foundation materials have arrived or are about to arrive. It is also recommended that a CRREL representative be available during the excavation to ascertain the areas requiring over-excavation of massive ice (wedge or relict ice).

All the fill material shall be clean, select fill gravel allowing for dense compaction, and possessing no more than 4% fines. The fill will extend beyond the perimeter of the building as noted above and may be gradually sloped away from the building at 2:1 horizontal to vertical. Positive drainage away from the perimeter of the building preventing surface flow beneath the structure is required. Care should be taken to insure that no down-wind topographic lows occur that may allow for accumulation of drifted snow which will not be removed under normal snow removal procedures. The accumulated snow will serve as a very efficient thermal insulator, and winter heat extraction will be reduced in those areas allowing for diminished temperature decrease in the subsurface.

1.3 Long Term Temperature Monitoring

For structures located on permafrost, long term temperature monitoring is important for analyzing the performance of the foundation system and aid future engineering decisions. It is recommended that for either foundation alternative, a minimum of six thermistor strings be installed from the surface down to an appropriate depth. For adfreeze pile foundations, at least two strings should be located down the entire length of the pile, while the other four may be obtain a shallower depth and be located away from the piles. For the footer and column foundation, all the strings should extend down to the bottom of the excavation, with some located near the columns, and some located away. When a final decision is made regarding the foundation type, the temperature monitoring design can be determined.

Si ev e

D ia m m m Ta re

Re ta in ed

P an

Re ta in ed g R et ai ne d Pa ss

P as s

3/ 4"

7.

0.

.7

.0

0.

.0

4.

1.

6.

.7

.3

0.

.7

3.

5.

.7

.8

0.

.0

0.

7.

.8

.2

0.

.7

0.

6.

7.

.7

.5

0.

.3

0.

0.

0.

.3

9.

0.

.7

0.

6.

6.

.5

.1

0.

6.

Pa n

2.

7.

.7

6.

To ta l

4.

0.

10203040506070809010

Percent Passing

FY

D or m

B

H Sa m pl e #1

G ra ve l

D

0.

S an d

.4

D

0.

F in es

6.

D

1.

Cu

.2 Cc

0.

010203040506070809010

0.

0.

Percent Passing

Pa rt ic le S iz e (m m

FY

D or m

B

H Sa m pl e #1

ERDC/CRREL LR 12-02

January 5, 2012 i

ERDC-CRREL Letter Report LR 12-02

Geotechnical Investigation

Kevin Bjella, MSc., P.E.

Cold Regions Research and Engineering Laboratory - CRREL

Engineer Research and Development Center – ERDC

January 5, 2012 ii

Regions Research and Engineering Laboratory (CRREL), and performed under MIPR #W16ROE-1069- 3123.

The author gratefully acknowledges the assistance of Dr. Edel Cortez (CRREL) for his review of this report, and Marc Beede (CRREL) for his valuable field assistance. The author would also like to thank Greenland Contractors personnel for their support during the field work of this project.

For more information contact:

Kevin Bjella

This report reflects the personal views of the author and does not suggest or reflect the policy, practices, iii

TABLE OF CONTENTS

1. INTRODUCTION

1.1 Scope and Purpose

1.2 Project Description

2. SITE CONDITIONS

2.1 Physical Setting

2.2 Site Description

2.3 Climate

2.4 Soils

2.5 Geology

2.6 Glaciology

2.7 Permafrost and Ground Ice

2.7.1. Matrix and Segregated Ice

2.7.2. Wedge Ice

2.7.3. Relict Ice

2.8 Active Layer

3. FIELD EXPLORATION

3.1 Borehole Drilling

3.2 Ground Penetrating Radar (GPR)

3.3 Laboratory Testing

3.4 Subsurface conditions

3.4.1. Drilling data

3.4.2. GPR data

3.4.3. Synthesis of Subsurface conditions

4. CONCLUSIONS AND RECOMMENDATIONS

4.1 Alternative I – Pile Foundation

4.2 Alternative II – Buried Footer and Column Foundation

4.3 Earth Work

4.3.1. Alternative I – Pile Foundation

4.3.2. Alternative II – Footer and Column Foundation

4.4 Long Term Temperature Monitoring

iv

APPENDIX A

APPENDIX B

APPENDIX C

BIBLIOGRAPHY

1. INTRODUCTION

1.1 Scope and Purpose

This report presents the results of the permafrost and geotechnical investigation of the proposed location for the FY13 Dormitory, at Thule Air Base (TAB), Greenland. This work was performed under

Military Interdepartmental Purchase Request (MIPR) W16ROE-1069-3123.

The scope of this work was to investigate the subsurface soil and rock conditions at the proposed footprint of the new dormitory, present those findings, and make recommendations for the foundation design. Ground penetrating radar (GPR) was performed in April 2011, and subsurface drilling was performed in July and August 2011.

1.2 Project Description

The US Army Corps of Engineers, New York District (CENAN) is tasked with the construction of a

3-story, 48-person dormitory at the Air Base. The proposed building is composed of a steel super-structure with insulated metal panel cladding, pitched metal roof, and a total square footage of 3250 sq.

meters. The anticipated life span of the structure is not specified.

2. SITE CONDITIONS

2.1 Physical Setting

The Air Base (Pituffik) is situated in the NW trending valley of Pitugfiup kugssua (North River).

This 12 km long valley is ice free, and drains the Greenland Ice Cap on the east, to North Star Bugt on the west. North Mountain bounds the lower reach of this valley on the north, with hilly terrain northward to

Wolstenholme Fjord. South Mountain bounds the lower reach of this valley on the south, with a relatively flat plateau southward to Parker Snow Bugt. The region is void of vertical vegetation and is restricted to low herbs, grasses, dwarf shrubs, mosses and lichens. Generally the surface in the valley surrounding the

Air Base has been disturbed by construction activities, and few undisturbed areas exist where surface soils and vegetation can be seen as they existed prior to the Air Base construction in 1951. As the valley rises in elevation toward the inland ice cap, the vegetation gives way to a very rocky, boulder strewn landscape.

2.2 Site Description

The project site is bound by 1st Street to the south west, Crescent Road to the south east, and an unnamed street to the north east that leads from the Fire Station to Northstar Inn. The site is currently occupied by Building 101 with numerous above-ground utility connections. These include insulated piping and electrical cables, which limited access to the north, and northwest of the site to drilling and

GPR. The site is on a high bench of the North River, with a slope towards the west and northwest. The

North River is approximately 250-m to the north. Building 101 sits on top of local fill material, averaging

1.5-m in thickness.

2.3 Climate

The climate at Thule AB is arctic marine, modified by the proximity to the inland ice cap. The mean annual air temperature (MAAT) is -11.0°C with occasional hurricane force winds. The average air thawing degree days (ATDD) for 1953 to 2008 is 428°C, and the average air freezing degree days

(AFDD) for the same period is 4414°C. The approximate length of the thawing season is 125 days from mid May to mid September. Air thawing and freezing indexes are a seasonal summation of the average number of degrees above freezing (thaw index) or below freezing (freeze index) for each day of the season. These indices are a convenient method to compare variation in climate from year to year, and for input into models for the prediction of thaw and freeze depth.

The indices are plotted in Figure 1 for the period from 1952 to 2011 of daily surface data from

Station #042020 Pituffik (Thule AB, Greenland), obtained through the U.S. National Climatic Data

Center. Some intervals of data were not available. Based on these indices, the thaw index has exceeded the average of 428 degree days C for the last 7 years, and the summer of 2009 was the third warmest since

1952. The average freeze index of 4414 degree days C has not been obtained for the last 9 years, and a possible trend towards warmer winters can be seen. A statistical analysis was not performed, however, if this trend is confirmed it would coincide with other Arctic observations which trend towards warming winters with approximately stable summers (IPCC, 2007).

Figure 1. Freezing Degree Days, Thawing Degree Days, and Mean Annual Air Temperature

(MAAT) plotted for 1952 to 2011.

2.4 Soils

The soil is predominately glacio-fluvial in origin, deposited during glacial occupation and retreat.

Therefore the soils range from silt size, to cobble and boulders but are predominantly gravel size. Particle size and ice content is often localized due to this depositional process, and a particular interval may not be traceable to within meters. However, in proximity to the North River, alluvial deposition has reworked the glacio-fluvial sediments and often provides greater continuity to the intervals, and this appears to be the case at this project site. The project site is located at a high terrace of the North River, therefore alluvial reworking of the sediments is expected. The temperature of the soil measured at a CRREL site near the

-16

-14

-12

-10

-8

-6

-4

-2

1951 1956 1962 1967 1973 1978 1984 1989 1995 2000 2005 2011

D eg re e

D ay s °C

Year

Thule AB Air Temperature Indices

AFD

D

ATD

D

0.5

1.5

2.5

3.5

-7.5 -5.0 -2.5 0.0 2.5 5.0 7.5

D ep th (m

Temp °C airfield, with barren fill for surface material, is shown in Table 1. Based on the results of four other

CRREL temperature measuring sites at TAB, the temperatures at the proposed site are not expected to deviate from those at the site near the airfield.

Table 1. Subsurface temperatures and plot for Sept. 20th, 2011.

2.5 Geology

The glacially sculpted geology of the region is dominated by an alternating sequence of sedimentary rocks, termed the Thule Supergroup. More specifically, the Upper Thule Supergroup is sediments comprised of the Narssarssuk Group and the Dundas group (Dawes, 2006). These siliciclastic redbeds and pale carbonaceous sediments are visible in the glacially eroded slopes of North and South Mountain, Dundas Fjeld, and Saunders Ø. The lithified sediments are essentially un-deformed, however half-grabben structures are numerous, displaying vertical displacements of tens to hundreds of meters. A regional swarm of basic dykes and sills are noted in this group, with a prominent exposure of Diorite having been cut for the TAB runway.

Depth (m) Temp °C

0.3 6.5

0.9 4.1

1.5 -0.5

1.8 -1.5

2.7 -4.0

3.0 -4.2

3.7 -5.1

This strata generally dips to the south-southwest at shallow angles, with the strike trending west-northwest, consistent with the trend of the North River Valley. This dipping strata is easily imaged with ground penetrating radar, and near the North River the bedrock surface, which is buried under glacial and alluvial sediments, can be seen dipping away from the river towards the south. Slate bedrock was encountered approximately 800-m upstream of the project site, on approximately the same terrace level and on the same side of the river as the project site. The depth to this bedrock was 4-m to 5-m. Due to the alignment of the river with the strike of local bedrock structure, it hypothesized that this bedrock terrace exists at the project site as well. Prominent exposures of the slate sequences can be found in the valley and leading up to, and at the BMEWS site. The layers are approximately 2 mm in thickness, dark colored, and smooth. Weathering provides ready detachment at the bedding boundary, and exposures are easily disturbed by hand and foot traffic. Borehole drilling into the weathered shale bedrock exposes clay size material embedded with angular shale fragments < 1.0 cm, and this will grade to pure clay with very low moisture (ice content).

2.6 Glaciology

The glacial history of the region described by Funder (1990) suggests that during the late

Pleistocene, multiple glacial advances covered the Pituffik Valley. The greatest extent of glaciation and the earliest recorded in the existing sediments, the Agpat Glaciation, extended westward beyond Saunders

Ø. The extent of the following inter-glacial is undetermined, but the ice is hypothesized to have retreated to Wolstenholm Fjord. The following glacial advance, the Narssarssuk Glaciation, filled Pituffik Valley and extended southwestward terminating on the plateau to the south of the valley, with the following inter-glacial hypothesized to have retreated to Wolstenholm Fjord. The next and last glacial advance, in the early Holocene, failed to progress from Wolstenholm Fjord, and no further advances in the valley are noted.

Due to the multiple glacial events, a large amount of till and outwash sediment overlie the sedimentary bedrock within Pituffik Valley. The glacial sediment thickness varies from 6-m to 18-m, with progressively thickening depth moving towards the North River drainage and existing ice cap margin, and thinning depth with a particle size grading to beds of sand when approaching the beaches of North Star

Bugt. Glacial tills of larger cobble and erratic are evident in the valley. Therefore the Air Base is situated on a varying thickness of glacial sediments, with an average of 3-m to 10-m at the airfield.

During the glaciations, alluvial sediments have been deposited along the channel of the North River. This deposition has re-worked the outwash and till into more stratified layers of silts, sands and gravels. These would be located up to the highest benches of the North River, to include the proposed location of the

FY13 Dormitory.

2.7 Permafrost and Ground Ice

A periglacial environment has existed in the High Arctic, through the Pleistocene and Holocene, and continues today, including the Pituffik Valley. During glacial retreat the sediments and rock are exposed to low temperatures, allowing for the establishment of permanently frozen ground (permafrost) and associated ground ice features. In the High Arctic such as Pituffik, the permafrost is continuous in lateral extent, and is estimated to be more than 300-m in depth. This permafrost was created epigenetically, where the rock and sediments were placed in near full thickness, then subsequently permanently frozen.

Ice exists in the permafrost and is the primary concern for the engineering of foundations for structures. If allowed to thaw, the greater the amount of ice present, the lower the shear strength of the soil will be upon thawing. This lower shear strength results in differential thaw settlement, and must be accounted for in design. Currently the permafrost temperature, at the depth of zero annual amplitude, is approximately -

10°C (Bjella, 2010).

2.7.1. Matrix and Segregated Ice

The freezing process during creation of the permafrost can create excess ice in the soil if the proper conditions exist. From a conservative standpoint, it is generally assumed that soils are saturated when they become permanently frozen. Therefore the 10% volume expansion that occurs to fresh water upon freezing will cause individual soil particles to be moved apart by this matrix ice. Fine grained soils contain more water (ice) at saturation than do coarser grained soils. Also, if fine grained soils (soils capable of wicking water) exist along with an additional supply of water, ice will be created at the freezing front, developing what is termed segregated ice. This creates near horizontal layers or lenses of ice millimeters to centimeters in thickness, and centimeters to meters in length. During the sediment deposition, either glacial or fluvial, the amount of water available was variable. Therefore it is not uncommon to find very high ice content soils directly above, below, or adjacent to soils with lower ice content.

2.7.2. Wedge Ice

Cold temperatures in the winter contract the surface soils and allow cracks to develop in the soil that are meters deep, tens of meters in length, and millimeters in width. Surface water in the spring and summer migrates into the cracks and freezes, creating a thin vein of ice. This location of ice intrusion is a zone of weakness, and the process will repeat at the same location for hundreds and thousands of years with the resultant ice vein becoming an ice wedge. These wedges can be meters in depth, one to two meters in width, and meters to tens of meters in length. Most often the wedges will interconnect into polygon shapes that are meters in diameter, and these shapes can be seen at the surface because of the mechanical distortion of the surface that occurs along with the ice intrusion. The Pituffik Valley has a high occurrence of wedge ice and the probability is very high for its existence at the project site.

2.7.3. Relict Ice

During glacial retreat, the margin of the ice sheet is very dynamic with glacial till being exposed and deposited, large volumes of water flowing off the ice sheet carrying outwash, and ice fracturing and being deposited on top and in loose piles of sediment. This fractured ice can be deposited and buried with sufficient expediency to prevent the ice from melting prior to the subsequent permafrost creation.

Therefore chunks of ice, termed relict ice (Corte 1962), can exist in the permafrost and in a very random manner. The North River channel however, moves such large volumes of water and sediment, that the probability of relict ice surviving in the benches that are now exposed near the river, and at the proposed

FY12 Dormitory location, is relatively low.

2.8 Active Layer

The active layer is the near surface soils that undergo the annual process of thawing in the summer and complete refreezing during the winter. The maximum thaw depth is the top of the permafrost table.

The depth of annual thaw is dependent on vegetative cover, soil type, soil moisture, and solar aspect. For

Pituffik Valley the active layer ranges from 30 cm depth in vegetative areas under thick organic cover, to

1.5-m to 2.0-m in non-vegetated areas. It is very common to find a thick sequence of segregated ice at the base of the active layer, and water perched on the top of the permafrost. This is due to the permafrost acting as an aquitard, and the collected water generally exceeds saturation of the soil.

3. FIELD EXPLORATION

3.1 Borehole Drilling

A total of four (4) boreholes (Fig. 2) were completed at the proposed site from August 1 to August 2, 2011, and all boreholes were logged by the author. The drill rig utilized was a Geoprobe 7822 DT, combined rotary and direct push technology (DPT) machine. This combined ability was specifically chosen to allow for direct ‘undisturbed’ sampling of the fine grained frozen soils and ice, while having the ability to quickly convert to air rotary or down-the-hole hammer, to allow penetration of ice-cemented gravels and larger cobble and boulders. Borehole logs are presented in Appendix A.

The MC5 Macro Corer DPT rod and barrel system utilizes a 5.7cm diameter, 1.5-m sample barrel that allows for sample capture into a clear acrylic sample tube. If conditions are favorable, 1.5-m of recovery is possible with minimal thawing of the samples due to friction. DPT is a misnomer as the barrel is not pushed into the soil, but rather it is hammered into the soil at very high frequency. After retrieval the plastic tube is cut lengthwise into halves to allow for sampling and logging. With above freezing ambient air temperatures the sample will begin to thaw, allowing for a visual approximation of ice-rich vs. ice-poor intervals. Full recovery occurred in all intervals, in all the boreholes excepting the lower two intervals in BH-2 at 60% and 70% respectively. Refusal was encountered during DPT sampling in one interval of BH-3, and in two intervals of BH 4. Changing to air rotary with tri-cone roller bit allowed for penetration of the resistive zone, then DPT was resumed to obtain continuing samples.

The air rotary drilling system consisted of NWJ rod (7 cm diameter) with tri-cone roller bit engagement. The compressed air was supplied by a Thule Air Base provided, Atlas Copco XAHS-1146 screw compressor, with 540 l/s flow at 20 bar. As mentioned previously, two intervals of DPT refusal occurred in BH-4, and for the lower interval it was decided to continue with the air rotary as far as possible to ascertain if bedrock would be encountered. A high amount of loud scratching and bouncing of the drill system occurred, and this was accompanied by a moderate penetration rate of 3.0 cm/min.

Drilling conditions and advance rates such as this indicate that ice-rich frozen gravels are being drilled.

Figure 2. Borehole locations around Bldg. 101.

3.2 Ground Penetrating Radar (GPR)

Ground penetrating radar surveys were conducted at the proposed site April 23 and April 28, 2011. A

Geophysical Survey System (GSSI) SIR-3000 GPR was utilized with 200 MHz, and 400 MHz antennas.

The 200 MHz antenna provided the best resolution vs. depth of imaging, and all the images illustrated in this report are of that frequency unless noted. The surveys were performed in April while the active layer was completely frozen to insure no attenuation from liquid water would affect the signal. Berms and drifts of snow prevented creating a larger grid extending around the back of the building, and no snow removal was performed in this area.

Two grids were laid out in two areas adjacent to the existing Building 101. Grid #1 was 50-m x 5-m, and was positioned on the southwest side of the building, in the parking area running parallel to the building, and 1st Street (Fig. 3). The western corner of the grid was created as the origin (0-m,0-m), and the eastern corner of the grid (50-m x 5-m) is adjacent to the south corner of the building. Along the Y-axis, 1m intervals were located; and along the X-axis, 2m intervals were located. Grid #2 was located along the southeast side of the building (Fig. 3). This grid was 20-m x 4-m, with (0-m,0-m) located southeast of the eastern corner of Grid #1, and (20-m, 4-m) located at the eastern corner of the building

(Fig. 3). Along the Y-axis, 1-m intervals were located; and along the X-axis, 2-m intervals were located.

Both grids were surveyed in the same manner starting at (0,0) and surveying along the X-axis to the end of that line. The next line was advance 1m along the Y-axis and surveyed in the same direction, and this was repeated across the grid. The survey was then run orthogonal to the previous lines, starting at

(0,0) and moving along the Y-axis. For both grids the Y-axis lines were run at 10-m intervals and were all run in the same direction. Selected radargrams, Figures 9 thru 12, are shown in Appendix B.

Figure 3. Grid layouts for GPR surveys at Bldg 101.

Grid 1

(0m,0m)

(0m,0m)

3.3 Laboratory Testing

During logging, samples were obtained from specific intervals of interest. The samples were field logged, bagged and sealed. Later that day they were weighed and placed in a sample oven at 110°C

(ASTM D2216), which was available at Thule. Moisture content was then determined after sample drying by dividing the weight of the moisture, by the weight of the dry sample, and is expressed as a percentage.

Particle size distribution has not been performed on the samples obtained from these boreholes. It is recommended that a particle size distribution be obtained from Baker (2004) for FY05 Dormitory, and be used as an approximation of the soils at this site. The samples used for the moisture content analysis were retained and shipped to our laboratory and a particle size analysis can be performed if required.

Due to the difficult logistics from Thule AFB, it was decided that the shipping of intact frozen samples to our laboratory could not be counted upon, therefore no dry unit weights were measured. For the geotechnical investigation at the FY05 Dormitory site 75-m from this project site (Baker, 2004), one dry unit weight was measured at 1034 kg/m^2 with a moisture content of 31%. Another investigation conducted near the airfield (Shannon and Wilson, 1983) measured eight dry unit weights with an average of 1872 kg/m^2 and an average moisture of 16%. Salinity of the soils was not tested for this site. Baker

(2004) revealed that although Thule Air Base is in close proximity to the sea, there are not elevated salinity levels at this location between the North River and the airfield. No strength measurements were conducted on bedrock samples.

3.4 Subsurface conditions

3.4.1. Drilling data

A total of four subsurface borings were completed during this investigation (Fig. 2). The boring logs are located in Appendix A, and selected photos of the cores are shown in Figures 13 thru 26 in Appendix

C. Building 101 is located on man-placed fill, and the surface elevation at each boring was approximately the same. The natural surface elevation beneath the fill material gradually decreases moving from southeast to northwest. All four of the borings were performed to give detailed information from the surface down to refusal, and BH-4 was drilled to penetrate beyond the DPT refusal depth, and ascertain the thickness and material being encountered. Soil moisture (ice content) was visually examined and logged for each 1.5-m Macro core recovered, and 12 specific samples were measured analytically from key intervals. The gravimetric moistures for 5 of the 12 samples were greater than 50%, and these samples were taken from between 3.0-m and 5.5-m, indicating a very ice-rich zone starting just below the active layer extending down to at least 6.0-m in BH-1, at least 6.0-m in BH-2, at least 4.5-m in BH-3, and down to 6.0-m in BH-4. This correlates with the borings conducted for the FY12 Dorm (Bjella 2012a).

The stratigraphy encountered in this high ice content zone is variable, and the individual specific layers are not easily correlated to adjacent boreholes. It was expected that these sediment horizons would be heterogeneous within relatively short distances and smaller scales (tens of centimeters), specifically with regard to gravel size, sand size, and ice content. Generally speaking however, the soils within this horizon are silty gravels with some sand constituent, they frequently contain segregated clear ice at varying depths, and generally they are gray indicating a lack of oxidation due to a reduced environment after permafrost creation. No wedge ice was encountered in any of the borings, however this is not meant to suggest that ice wedge complexes do not exist at this site. On the contrary, it is expected that ice wedge complexes do exist at this site, as was discovered in the investigation for the FY12 Dorm (Bjella, 2012a) and the Consolidated Engineering Facilities investigation (in press).

Below the 5.5-m to 6.0-m depth in BH-4, it was found that drilling resistance increased dramatically, with the DPT. Moisture samples were taken in this interval in BH-4 where the moisture at 7.0-m and 7.5-m was 12.3% and 12.5% respectfully. Less ice is correlated to stiffer drilling with the DPT. Full recovery occurred in all intervals of all the boreholes, excepting the lower two intervals in BH-2 at 60% and 70% respectively. Refusal was encountered during DPT sampling in one interval of BH-3, and in two intervals of BH 4. Changing to air rotary with tri-cone roller bit allowed for penetration of the resistive zone, then

DPT was resumed to obtain continuing samples.

The two locations for DPT refusal in BH-4 were 6.1-m and 7.8-m.