Changho Choi, PhD., PE Joonyong Lee, Tae-Hyung Kim, Sung-Gyu Ko

Korea Institute of Construction Technology

IWM 2014 Krakow, Poland June 12, 2014

Design Parameters of Micropile in Permafrost Sandy Ground

Contents

1. Research overview

2. Research objectives

3. Experimental test

4. Test results

5. Conclusion and future work

6. Why micropiles?

1) Engineering Characteristics of Frozen Ground - Classification of frozen ground

a. Seasonal frozen ground – Freezing during winter season at the surface

b. Permafrost – Frozen ground regardless of season

- Ground temperature of permafrost

Permaf rost layer

Unf rozen layer

Act ive layer

Ground Temp. Distribut ion of Permaf rost

1. Research Overview

4

1. Research Overview 2) Definition of Adfreeze Bond Strength

- Adfreeze bond (adfreezing) : Bonding of frozen soil and other materials

- Adfreeze bond strength : Maximum stress measured during tangential

failure between frozen soil and other materials

Pi l e

So i l

Ice Bonding of Ice bar and tongue

is a kind of ADFREEZING

Design Parameter for Pile Foundation in Frozen Ground

Design Step

Bearing Capacity Estimation Uplift Force Check Creep

Loading condition

Weight+ Down drag force due to thawing

< Adfreeze Strength

Uplift adfreeze bonding force due to freezing

< Weight + Adfreeze Strength

Creep settlement

Check

Weight P

P I L E

3) Pile Design in Frozen Ground

1. Research Overview

Summer

adQ

Down drag force due to ground

thawing

Adfreeze bond strength

dfQ

Winter

Uplift adfreeze force due to

ground freezing

Adfreeze bond strength adQ

adQ

Material Type rs

Steel 0.6

Concrete 0.6

Uncreosoted Timber 0.7

Corrugated Steel 1.0

6

2. Research Objectives 1) Weaver and Morgenstern(1981) fsa r ττ ×=

2) In this study

Soil types and freezing temperature were not considered

Suggest a reasonable method to characterize the shear strength of the frozen soils and the adfreeze bond strength with different normal stress and freezing temperature conditions.

Obtain rs with different soil types and freezing temperature condition and compare it past research

Provide a key parameters for design of pile in cold regions

1) Freezing Chamber

- Temp. Control upto -20 degree Celsius with ±1 degree precision

- Size of chamber : 2000mm(W)×3000mm(L)×2500mm(H)

10/34

3. Experimental Test

2) Direct Shear Device for Frozen Soils - Working Temperature for the all parts : Max -30℃

- Horizontal Displacement Speed : 0.5mm/min

- Shear Box size : 100mm×100mm×40mm (Height)

- Working Temperature for the all parts : Max -30℃

- Horizontal Displacment Speed : 0.01mm/min

- Shear Box size : 100mm×100mm×40mm (Height)

10/34

3. Experimental Test

0

20

40

60

80

100

0.01 0.1 1 10

Pas

sing

Per

cent

age

(%)

Particle Diameter (mm)

Joomoonjin Sand

Weathered Granite

3) Soil Properties - Use two type of soils; 1) standard sand (Joomoonjin Sand), 2) weathered

granite soil which is classified as SW with 10% of #200 passing particles

J.M. W.G

Gs 2.65 2.67

emax 0.997 1.227

emin 0.596 0.418

D50 0.56 0.71

Cu 1.53 6.07

Cc 0.94 1.29

USCS SP SW

#200 0 ~10

Dr(%) 77 76

S(%) 100 67

w(%) 24 15

3. Experimental Test

10

3. Experimental Test 4) Shear Strength Test Procedure

- Fill the shear box with three layers (controlled with weight of soil for each

layer) and compact with three different compacting devices

- Saturate the specimen in water tank for 24hrs, place on the shear device

inside chamber and then freeze it to target temperature for 24hrs.

Compactor Compactor Compactor

Three Layer Compactors

11

3. Experimental Test 5) Adfreeze Bond Strength Test Procedure

- Specimen is prepared by inserting the aluminum pedestal at the bottom of

shear box and fill the half of shear box with soils

- Again, saturate the specimen in water tank for 24hrs, place on the shear

device inside chamber and then freeze it to target temperature for 24hrs.

i) Inserting the aluminum ii) Filling with sand iii) Compaction

12

3. Experimental Test 6) Failure shape of shear strength and adfreeze bond strength test

After failure

Top Bottom

13

4. Test Results Freezing

Temperature (℃)

Vertical Stress (kPa)

Joomoonjin Sand Weathered granite soil Shear Strength

(kPa) Adfreeze Bond Strength(kPa)

Shear Strength (kPa)

Adfreeze Bond Strength(kPa)

0 100 82 42 263 81 0 200 146 69 291 137 0 300 236 88 355 210 -2 100 1624 239 543 123 -2 200 1781 323 667 231 -2 300 1941 430 863 298 -5 100 2824 665 1469 330 -5 200 3160 816 1690 389 -5 300 3519 915 1912 464

-10 100 4596 1150 2350 660 -10 200 5137 1294 2577 864 -10 300 5456 1445 2921 895 -15 100 - - 2916 961 -15 200 - - 3050 1056 -15 300 - - 3293 1105

Both shear strength and adfreeze bond strength of two soils increases as the temperature went down and normal stress increased.

Both shear strength and adfreeze bond strength of Joomoonjin sand were smaller than those of weathered granite soil at 0℃, whe re a s tho s e o f Jo o mo o mjin s a nd we re la rge r tha n tho s e o f we a the re d gra nite s o il be lo w - 2 ℃ .

This wa s due to diffe re nt ic e binding c a pa c ity with s o il pa rt ic le s , a nd wa s s tro ngly a ffe c te d by a highly c o mple x inte ra c t io n be twe e n the s o lid s o il s ke le to n a nd the po re ma trix, c o mpo s e d o f ic e a nd unfro ze n wa te r.

14

4. Test Results

0

1000

2000

3000

4000

5000

6000

7000

-15 -10 -5 0

Stre

ngth

(kP

a)

Temperature (℃)

Shear strength of frozen soilAdfreeze bond strength

τf(T)=-22.97T 2-683.37T+82.00R2=0.97

τa(T)=-1.44T 2-125.85T+41.00R2=0.99

0

1000

2000

3000

4000

5000

6000

7000

-15 -10 -5 0

Stre

ngth

(kP

a)

Temperature (℃)

Shear strength of frozen soil

Adfreeze bond strength

τf(T)=-5.06T 2-254.45T+263.49R2=0.99

τa(T)=0.21T 2-57.57T+81.06R2=0.97

0

1000

2000

3000

4000

5000

6000

7000

-15 -10 -5 0

Stre

ngth

(kP

a)

Temperature (℃)

Shear strength of frozen soilAdfreeze bond strength

τf(T)=-25.94T 2-791.02T+236.00R2=0.99

τa(T)=-5.46T 2-190.75T+88.00R2=0.99

0

1000

2000

3000

4000

5000

6000

7000

-15 -10 -5 0

Stre

ngth

(kP

a)

Temperature (℃)

Shear strength of frozen soil

Adfreeze bond strength

τf(T)=-10.75T 2-358.63T+355.45R2=0.99

τa(T)=0.0014T 2-61.31T+210.19R2=0.98

◎ Joomoonjin Sand

100 kPa

◎ Weathered Granite

100 kPa

300 kPa 300 kPa

Adfreeze bond strength showed a similar pat tern to shear strength characterist ics, even though increment of adfreeze bond strength due to temperature and normal stress condit ions was dif ferent f rom that of shear strength.

Shear strength of two frozen soils increased dramatically unt il - 10℃, but increase rate of those converged between - 10℃ and - 15℃.

0.0

0.2

0.4

0.6

0.8

-15-10-50

r s(=τ a

/τf)

Temperature (℃)

100 kPa200 kPa300 kPa

15

4. Test Results

0.0

0.2

0.4

0.6

0.8

-15-10-50

r s(=τ a

/τf)

Temperature (℃)

100 kPa200 kPa300 kPa

◎ Joomoonjin Sand ◎ Weathered Granite

• The coefficient rs decreases at temperature range between 0 and -5 degrees Celsius, and the ratio becomes constant as temperature decreases below -5 degrees Celsius.

• This indicates that the temperature condition has an influence on the proportional coefficient in initial freezing condition.

• Also, the normal stress condition has an influence on the proportional coefficient in initial freezing condition in case of weathered granite soil.

0

0.2

0.4

0.6

0.8

1

0 100 200 300 400

r s(=τ

a/τf)

Normal Stress (kPa)

Result of this study(Joomoonjin sand)Result of this study(weathered granite soil)Weaver and Morgenstern(1981)Ladanyi and Theriault(1990)

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4. Test Results ◎ Coefficient rs from this study and previous studies at -2℃

• Both shear strength and adfreeze bond strength characteristics of frozen soils are governed by the intrinsic material properties such as grain size, ice and water content, air bubbles, and by externally imposed testing conditions such as temperature, freezing time, and strain rate.

• This means that field environmental conditions should be considered in determination of shear strength and adfreeze bond strength characteristics.

• In this study, direct shear testing inside of a large-scale freezing chamber was conducted in order to analyze the shear strength and adfreeze bond strength characteristics with varying freezing temperatures and normal stress with two soil types, and the relationship between the adfreeze bond strength and shear strength of frozen soils was analyzed in terms of ratio rs.

• The test equipment described in this paper provides a promising approach to obtaining foundation design parameter, adfreeze bond strength, in frozen ground.

• According to our test results the previous proportional coefficients describing the relationship between shear strength and adfreeze bond strength should be used in care to obtain true adfreeze bond strength characteristics in all conditions.

• For pile design in frozen ground, it is recommended to compare the design parameters from several research results and obtain the most suitable one for the field conditions.

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5. Conclusion and Future Works

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Material Fractal Dimension

Steel 1.08-1.09

Concrete 1.07-1.12

cement paste 1.033

Mortar 1.060

Fractal Dim. For Constr. Mat. (Brandt and Prokopski, 1993)

5. Conclusion and Future Works

Df = 1 Df = 2 ≤ ≤

Ste e l

C o n c re te

m (Weaver and Morgenstern, 1981)

fsa r ττ =

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6. Why Micropiles?

• This research work can be generally applied for foundation design in permafrost area such as Siberia, north Canada, etc.

• S. Korea has built a new Antarctic research station, JanBoGo research base in this Feb. and there is a need to small pile construction technology because the transportation of construction machine is key issue. That is why micropile method has got interest.

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세계 지도, Route 표시

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Korea- Paris(12hr)- Sant iago(15hr)- Punta Arenas(4hr) – Anta rc t ic Chile

Ba s e - King Se jo ng Ko re a Sta t io n (1hr)

6. Why Micropiles?

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6. Why Micropiles? -

KSJ

JangBoGo

22

6. Why Micropiles? -

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6. Why Micropiles? -

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6. Why Micropiles? -

Elevated Building

25

6. Why Micropiles?

26

Gentoo Penguin

27

Who is Bad Guy?

Thank You!

Pu(=πdLf)≤ P+Wp+Pt+Ps Lf : depth of frozen layer in active zone Lt : depth of thawed layer in active zone Le : depth of permafrost zone Wp : weight of foundation P : downward load Pt : downward skin friction force of thawed layer in active zone Ps : downward skin friction force of permafrost zone Pu : upward skin friction force of frozen layer in active zone τu : adfreeze bond strength of frozen layer in active zone

P+Wp+Pd ≤Ps(=πdLe τa) La : depth of active layer Le : depth of permafrost zone Wp : weight of foundation P : downward load Pd : downward skin friction force of active layer Ps : upward skin friction force of permafrost zone τa : adfreeze bond strength of active layer

2. Pile Design in Frozen Ground