ralph rollins, performed geotechnical … rollins, performed geotechnical investigations for over...

Ralph Rollins, performed geotechnical investigations for over 5000 structures

I took Soil Mechanics class from my Father

Rachel Rollins is a Civil Engineering student

Rachel took Soil Mechanics class from her Father

Granddaughter, Ella, shows early interest in soil behavior…

Pile Foundations in Liquefied Soil

Kyle M. Rollins

Civil & Environmental Engineering Department Brigham Young University

Provo, Utah, USA

Liquefied Sand

Stiff Clay

Piles in Level Ground

Stiff Clay

Non-Liquefied SandLiquefied Sand

Non-Liquefied Sandon-Liquefied Sandon-Liquefied SandLiquefied Sandquefied Sandquefied Sand

Stiff Clayff Clayff Cl

Piles in Sloping Ground

24.96 m 75.02 m 75.24 m

176.14 m

Rio Estrella Bridge, Costa Rica, 1991

H

Lateral Load Analysis for Piles with p-y Curves

Non-linear springs

p

p

p

p

p

y

y

y

y Interval

y

y

y

y

y

1

2

3

4

5

y

Passive Force on Bridge Abutments

Liquefaction

Lateral Spread Displacement Driven by Passive Force

Modeling Lateral Spreading Free-Field Displacement Profile

Non-liquefied

Liquefied Zone

DH

Forc

e

Displacement

Research Sponsors

Eight State DOTs FHWA NSF PDCA ADSC

“One good test is worth a thousand expert opinions.” Werner Von Braun

Designer of Saturn V Moon Rocket

Healthy Skepticism for Tests A theory is something nobody believes, except the person who proposed it. An experiment (test) is something everybody believes,

--Albert Einstein

performed it except the person who

“The trouble with quotes on the internet is that it’s difficult to discern whether or not they are genuine.” --Abraham Lincoln

Elevation View of Test Site

40 ft

Liquefied Sand

Non-Liquefied Sand

15 ft

3x3 Pile Group 3 ft Drilled Shaft

High-Speed Hydraulic Ram

Think you used enough dynamite there Butch?!?

Treasure Island Naval Station

Test Site

Site Characterization

Field Testing Cone Penetration Testing (CPT, Visioncone) Standard Penetration Testing (SPT) Dilatometer Testing (DMT) Pressuremeter Testing (PMT) Shear Wave Velocity Testing Radar Tomography

Lab Testing Atterberg Limits Grain Size Distribution Undrained Strength Testing

0 2 4 6 8 10 12 14

CPT Cone Resistance, qc1 (MPa)

MeanMean-SDMean+SD

0 10 20 30

SPT Blow Count, N1(60)(Blows/300 mm)

0 20 40 60 80 100

Relative Density, Dr(%)

From CPT

From SPT

Interpreted Soil Profile

0

1

2

3

4

5

6

7

8

9

10

Dept

h Be

low

Exc

avat

ed S

urfa

ce (m

) Interbedded Fine SandandSilty Sand(SP-SM)

Fine Silty Sand (SM)

Gray Silty Clay (CL)

Sand (SP)

Fine Sandw/ Shells(SP)

Test Section Layout

Pilot LiquefactionTest Site

Single Pipe Pilevs H Pile

2x2 Pile Groupvs 0.6 m CISS

3x3 Pile Groupvs 1.0 m CISS

Blast Charge Pattern

Blast Holes

Bored Pile Driven Pile Group

Piezometers

Placing the Explosive Charges

Results from Pilot Liquefaction Test Pattern of 16 explosive charges (1 lb at 12 ft depth) acceptable. Liquefied test volume 20 ft thick, 36 ft wide and 50 ft long. Ru > 0.8 can be maintained for 4 to 6 min. Pressure transducers can survive blast and measure residual pore water pressure. Vibration levels will not cause damage

Single Pile Test

Load vs Deflection Curves for Single Pipe Pile

-100

-50

0

50

100

150

200

250

-50 0 50 100 150 200 250Displacement (mm)

Load

(kN)

Non-LiquefiedLiquefied

--4400

-20

0

20

40

6600

80

111000000

RRuuu (%%

)

0 120 240 360 480 6000 120 240 360 480 60

Time (sec)

-50

0

50

100

150150

200

0 120 240 360 480 600

Time (sec)

Load

((kN

)

τ = (σ - u) tan

Comparison with Lab Tests

Boulanger et al (UC-Davis)

Moment Before & After Liquefaction

-2

0

2

4

6

8

10

12

-100 0 100 200 300 400 500

Moment (kN-m)

Dept

h Be

low

Exc

avat

ed G

roun

d (m

)

Before Liquefaction

After Liquefaction

Generalized p-y Curves

Generalized p-y Curves

Ru≈100%

Ru≈ 60-70%

Computed vs Measured

Response

Undrained Strength Approach for Liquefied Sand

Horizontal Displacement, y

Hor

izon

tal R

esis

tanc

e/Le

ngth

, P

Ultimate Strength based on Residual Strength

Soft clay curve shape

Residual Strength for Liquefied Sand

P-multiplier Approach for Liquefied Sand

Horizontal Deflection, y

Hor

izon

tal F

orce

/Len

gth,

p

Non-Liquefied Sand Curve

Liquefied Sand Curve using P-multiper of 0.1 to 0.3

0 25 50 75 100 125 150 175 200 225 250Deflection at Load Point (mm)

0

10

20

30

40

50

60

70

Pile

Loa

d (k

N)

Markers = Measured Values Relative to Zero Pile Head Load

P-Mult = 0.3 Sr Average P-Mult = 0.1 Calculated

Sr Lower Bound

Comparison of p-y Curves for Liquefied Sand

No Soil Resistance

Bending Moment Comparisons Undrained Strength Approach

Measured Developed p-y Curves Pile Only (no soil resistance)Average Lower-bound

Residual Undrained Shear Strength Approach

0 50 100 150Bending Moment (kN-m)(A) Pile Load = 15.0 kN

Dep

th B

elow

Loa

d Po

int (

m)

0

11

10

9

8

7

6

5

4

3

2

1

Dep

th B

elow

Gro

und

Surf

ace

(m)

0 100 200 300Bending Moment (kN-m)(B) Pile Load = 30.5 kN

Dep

th B

elow

Loa

d Po

int (

m)

Dep

th B

elow

Gro

und

Surfa

ce (m

)

0 200 400 600Bending Moment (kN-m)(C) Pile Load = 60.0 kN

Dep

th B

elow

Loa

d Po

int (

m)

Dep

th B

elow

Gro

und

Surfa

ce (m

)

Measured Developed p-y Curves Pile Only (no soil resistance)P-mult = 0.3 P-mult = 0.1

Sand P-Y Curve with P-multiplier Approach

0 50 100 150Bending Moment (kN-m)(A) Pile Load = 15.0 kN

Dep

th B

elow

Loa

d Po

int (

m)

0

11

10

9

8

7

6

5

4

3

2

1

Dep

th B

elow

Gro

und

Surfa

ce (m

)

0 100 200 300Bending Moment (kN-m)(B) Pile Load = 30.5 kN

Dep

th B

elow

Loa

d Po

int (

m)

Dep

th B

elow

Gro

und

Surfa

ce (m

)

0 200 400 600Bending Moment (kN-m)(C) Pile Load = 60.0 kN

Dep

th B

elow

Loa

d Po

int (

m)

Dep

th B

elow

Gro

und

Surfa

ce (m

)

Bending Moment Comparisons P-multiplier Approach

Different p-y Curves for Liquefied Sand

Horizontal Displacement, y

Hor

izon

tal R

esis

tanc

e/Le

ngth

, P

Liquefied Sand Based on Soft Clay Curve

Liquefied SandSuggested by Treasure Island Testing

Equation for p-y Curves in Liquefied Sand

where: A = 3 x 10-7 (z + 1) 6.05 B = 2.80 (z + 1) 0.11 C = 2.85 (z + 1) -0.41 z = depth in m = σ’o/γw Published in Jan. 2005 ASCE GGE Journal Incorporated in LPILE and GROUP programs

p = A(By)C for Dr ≈ 50%

Note: p in kN/m and y in mm.

Conclusions from Single Pile Tests

Controlled blasting technique provides a new method for evaluating liquefaction behavior in-situ. Lateral resistance develops due to negative pore pressure at large deflections. P-y curve shape is concave up and significant movement required to develop p. P-y curve shape stiffens with depth and as water pressure decreases. Equations developed to produce p-y curves and which produce good agreement with measurement.

Pile Diameter Effect

4 Pile Group vs 2 ft CISS Pile

Cast-in Steel Shell

(CISS) Pile

2200 kN Actuator

Sub-Frame

Driven Piles

Load Frame

4 Pile Group Video

9 Pile Group vs 3 ft CISS Pile

Cooper River Bridge Charleston, South Carolina

New Bridge-Completed July 2005

Longest Cable-stayed bridge in North and South America

Typical Soil Profile

Sandy soils susceptible to liquefaction

0

5

10

15

20

Dep

th (m

)

Cooper Marl (CH)stiff to very stiffAvg. N=15, 40%<w<50%50%<LL<150%, 20%<PI<80%

Silty Sand (SM) and Clayey Sand (SC) Avg. N=7, w=30%

Sand (SP), fine, loose to medium dense, Avg. N=12

Sandy Clay (CH), soft, w=106, LL=104, PI-69

Sand (SP), loose, fine, Avg. N=6, 0.5 to 28% Fines

Sand (SP) to Silty Sand (SM), Loose, fine, Avg. N=5

CPT Profile & Relative Density Interpreted Soil Type

0

5

10

15

0 10 20 30D

epth

(m)

Cooper Marl (CH)

Silty Sand (SM) and Clayey Sand (SC)

Sand (SP)

Clay (CH)

Sand (SP)

Sand (SP) to Silty Sand (SM)

Relative Density

0

5

10

15

0 20 40 60 80 100

Dr (%)

MPS-7GT-1LTB-1

Friction Angledegrees)

0

5

10

15

30 32 34 36 38 40 42 44

MPS-7GT-1LTB-1

Test Site Location

Test Site

Mt. Pleasant

Charleston

Blasting and Piezometer Layout

BYU Piezometer

AFT Piezometer

Druck Piezometer

Blast Holes

Load Direction

1st Ring1.83 m R 2nd Ring

7.32 m R3rd Ring10.36 m R

4th Ring14.63 m R

5th Ring17.68 m R

A107.92 m

AD31.83 m

A76.40 m

A83.35 m B7

4.88 m A910.97 m

A114.88 m

A124.88 m

AD17.92 m

AD21.83 m

A53.35 m B6

4.88 m A610.97 m

A19.30 m

B26.40 m

B33.35 m

B41.83 m

B54.88 mA310.97 m

Inner Blast Ring3.96 m R

Outer Blast Ring4.57 m R

MP1

Piezometer

Blast Holes

Test Set-Up

8.5 ft Test Shaft

2 – 500 kip Hydraulic Actuators Reference

Beam

Vertical Pore Pressure Distribution

0

2

4

6

8

10

12

0% 20% 40% 60% 80% 100% 120%

Excess Pore Pressure Ratio, Ru

Dept

h (ft

)

Inner Ring(1.83m)Middle Ring(7.32m)Outer Ring(10.36m)

Load-Displacement Curves

-3000

-2000

-1000

0

1000

2000

3000

4000

5000

-2 0 2 4 6 8 10 12 14 16Deflection (cm)

Load

(kN)

Pre-blastFirst BlastSecond Blast

Moment versus Depth Curves -5

0

5

10

15

20

25

30

35-5000 0 5000 10000 15000

Moment (kN-m)

Dept

h (m

)

1285 kN, pre-blast, cycle11294 kN, f irstblast, cycle11293 kN, secondblast, cycle1

(a) Cycle 1 from all three tests

Depth of Liquefied Sand

Equation for p-y Curves in Liquefied Sand

where: A = 3 x 10-7 (z + 1) 6.05 B = 2.80 (z + 1) 0.11 C = 2.85 (z + 1) -0.41 z = depth in m Pd = adjustment factor for pile diameter

p = Pd A(By)C

Note: p in kN/m and y in mm.

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=0.2m

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=1.5m

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=2.3m

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=3.0m

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=4.6m

0 50 100 150y (mm)

0

25

50

75

100

125

p (k

N/m

)

z=6.1m

Pile Diameter Effects on p-y Curves 0.9 m Pile 0.324 m Pile with Pd = 5.56

Comparison of Computed and Back-Calculated p-y Curves

-200

-100

0

100

200

300

400

0 1 2 3 4 5 6 7Deflection, y (cm)

p (k

N/m

)

Charleston (1 m, Ru=69%)

Computed (Pd=9, Ru=95%)

-200

-100

0

100

200

300

400

500

0 1 2 3 4 5 6 7Deflection, y (cm)

p (k

N/m

)

Charleston (5.9 m, Ru=85%)


Sand

(Dr=50%)

0

200

400

600

800

1000

1200

1400

0 1 2 3 4 5 6 7Deflection, y (cm)

p (k

N/m

)



Silty Sand

(Dr=35%)(Dr=45%)

0

500

1000

1500

2000

2500

0 1 2 3 4 5 6 7Deflection, y (cm)

p (k

N/m

)



Silty Sand

(Dr=35%)(Dr=45%)

0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6 7Deflection, y (cm)

p (k

N/m

)

Charleston (13.2 m, Ru=??)


Sand

(Dr=50%)

Adjustments to p-y Curve for Diameter

0

2

4

6

8

10

0 1 2 3

Pile Diameter, d (m)

P d -

Mul

tiplie

r for

Dia

met

er

TestsEquation

P d = 3.81ln (d) + 5.6

Treasure Island

Charleston

Comparison of measured moments and deflections with those computed by LPILE

-5

0

5

10

15

20

25

30

35-10000 0 10000 20000 30000

Moment (kN-m)

Dept

h (m

)

LPILE Moments

Moments derivedfrom Curvatures

-5

0

5

10

15

20

25

30

35-5 0 5 10

Deflection (cm)

LPILE Deflections

Deflections derivedfrom CurvaturesMeasuredDeflection

Applied Load = 1840 kN

-5

0

5

10

15

20

25

30

35-10000 0 10000 20000 30000

Moment (kN-m)

Dept

h (m

)

LPILE Moments


-5

0

5

10

15

20

25

30

35-5 0 5 10

Deflection (cm)

LPILE Deflections



-5

0

5

10

15

20

25

30

35-10000 0 10000 20000 30000

Moment (kN-m)

Dept

h (m

)

LPILE Moments


-5

0

5

10

15

20

25

30

35-5 0 5 10

Deflection (cm)

LPILE Deflections



Conclusions Regarding Pile Diameter Effects

Resistance increases non-linearly with pile diameter. Simple multiplier can reasonably account for diameter effects on p-y curves in liquefied sand.

Soil Density Effects

Comparison with Centrifuge Test Results(Wilson, 1998)

Dr ≈ 55%

Dr ≈ 35-40%

Comparison with Large Shake Table Tests(Suzuki and Tokimatsu, 2003)

Dr=60% Dr=35%

Test Layout at Tokachi, Hokkaido Test (Ashford et al, 2006)

Soil Profile at Tokachi Test Site (Ashford et al, 2006)

Back-Calculated p-y Curves Tokachi Test (Ashford et al, 2006)

P-y curves for loose sand (Dr = 15-25%, (N1)60= 2 to 6 ) were essentially flat Suggests no residual shear strength following liquefaction Generally consistent with predicted residual strength

Hybrid p-y Curve (Franke and Rollins, ASCE JGGE April 2013)

p

y

TILT curves (Rollins et al 2006) Residual Strength Curve

(N1)60=10-12

Residual Strength Curve (N1)60=6

Hybrid p-y Curve (Franke and Rollins, ASCE JGGE April 2013)

Provides reasonable agreement with: Centrifuge Tests Large Shake Table Tests Blast liquefaction Tests

Typical error of ± 20% on moment and displacement Accounts for sand density and pile diameter effects

Schematic of Statnamic Test

Test Foundation

Statnamic Sled

Load Piston Combustion Chamber

Statnamic Load Testing After Liquefaction

100 Ton Statnamic Rocket Sled

8.5 ft Diameter Shaft, 150 ft deep

Charleston Statnamic Testing

Load vs Deflection Curves

-1000

0

1000

2000

3000

4000

5000

6000

7000

-20 0 20 40 60 80 100

Deflection (mm)

Load

(kN)

Load Test 3Load Test 2Load Test 1

Computation of Equivalent Static Force

Fstn = ΣMiai + ΣCivi + Fs

or

Fs = Fstn - ΣMiai - ΣCivi

Equivalent Static Response

Comparison with Static Response

-600

-400

-200

0

200

400

600

800

1000

1200

-1.0 0.0 1.0 2.0 3.0 4.0 5.0Deflection (in)

Load

(kip

s)

Static

Equivalent Static from Statnamic

Conclusions Regarding Dynamic Tests

Equivalent static resistance is consistent with measured resistance Liquefied soil provides additional resistance due to damping Damping ratios of about 30 to 35% for this case

Loss of Side Shear & Downdrag

Bearing Stratum

Liquefiable Soil

Non-Liquefiable Soil

End-Bearing

Side Shear

Applied Load

SSSSSSSSSSSSSSSSSSSSiiiiiiiiiiiiiiiiiiiddddddddddddddddddddeeeeeeeeeeeeeeeeeeee SSSSSSSSSSSSSSSSSSSShhhhhhhhhhhhhhhhhhhheeeeeeeeeeeeeeeeeeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrrrrrReduced Side Shear Liquefied Soil

Negative Side Shear

Project Objectives

Evaluate loss of skin friction during liquefaction Determine development of negative skin friction during liquefaction and reconsolidation Develop simplified procedure to account for effects

Downdrag during Liquefaction

Bearing Stratum

Liquefiable Soil

Non-Liquefiable Soil

End-Bearing

Side Shear

Applied Load

SSSSSSSSSSSSSSSSSSSSiiiiiiiiiiiiiiiiiiiddddddddddddddddddddeeeeeeeeeeeeeeeeeeee SSSSSSSSSSSSSSSSSSSShhhhhhhhhhhhhhhhhhhheeeeeeeeeeeeeeeeeeeeaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrrrrrrrrrrrrReduced Side Shear Liquefied Soil

Negative Side Shear

Dragload & Settlement for Liquefaction

Non-liquefied Soil

Liquefied Sand

Non-liquefied Soil

Positive Skin Friction

Negative Skin Friction

Settlement

Depth

Soil Settlement

PileSettlement

Load

Qp

QT

QT

Qp

Neutral Plane

Maximum Compressive Force

Vancouver Canada Test Site

MasseyTunnel

Downdrag Test Site (Canlex)

Vancouver

Geotechnical Soil Profile

Interpreted Soil Profile

0

2

4

6

8

10

12

14

16

18

20

22

Dept

h (m

)

Fine Sand(SP)

Sandy Silt/Silt(SM/ML)

Fine Sand(SP)/

Silty Sand(SM)

Sand(SP)

Cone Tip Resistance, qc

(MPa)0 5 10 15 20

Fricton Ratio, Rf(%)

0 1 2 3 4 5 6 7

Relative Density, Dr

0.00 0.25 0.50 0.75 1.00

Pore Pressure, u (kPa)

-50 50 150 250

Pile

Equivalent SPT (N1)60 is 10 in target zone and 17 near pile tip

Downdrag Test Set-up

-20

-10

0

10

20

30

40

50

60

70

80

Dep

th (f

t)-6

-3

0

3

6

9

12

15

18

21

24

Dep

th (m

)

Strain GaugesPiezometersBlast Charges

Loose Liquefied Sand

Silty Sand/Clayey Silt

Clean Sand

DenserNon-Liquefied Sand

Hydraulic Rams

Reaction Frame

Test Pile Reaction PilesReaction Piles

Silty Sand/Clayey Silt

Clean Sand `

`

Reaction Frame `

DenserNon-Liquefied Sand

Test Pile Reaction PilesReaction Piles

`

Loose Liquefied Sand

` `

Blast Liquefaction Video

Re-loading due to pile settlement

0

100

200

300

400

500

600

0 1000 2000 3000 4000 5000Time (sec)

Load

(kN

)

160 kN or 36 kips

Before Blast 2 min. After Blast 10 min. After Blast

Before Liquefaction

11 in

After Liquefaction

11 in

Pore Pressure Generation

0.00

0.20

0.40

0.60

0.80

1.00

1705 1710 1715 1720 1725 1730

Time (sec)

Exce

ss P

ore

pres

sure

Rat

io, R

u

21 ft

28 ft

35 ft

42 ft

55 ft

Re-loading due to pile settlement

0

100

200

300

400

500

600

0 1000 2000 3000 4000 5000Time (sec)

Load

(kN

)

160 kN or 36 kips

Side Shear Transfer

0

5

10

15

20

0 100 200 300 400 500 600 700Load in Pile (kN)

Dept

h (m

)

Just before blastingJust after blastingEnd of settlement

Liquefied Zone

≈ 160 kN Re-loading produces positive

friction

Schematic View of Behavior

o

Fs= Ktan σ´ As = βσ´As

Before Liquefaction

u = static water pressure

o o


Fs= βσ´As

Immediately After Liquefaction

Δu = σ´ β = 0 relative to σ´

≈ 0 o

o


Fs= βσ´As

During Reconsolidation

Δu is decreasing to zero β ≈ 0.5β before liquefaction

o

Pile Settlement

Increased load in pile from dragload was carried by increased side resistance below the liquefied zone Increased dragload led to 7 mm (0.27 in) of pile head settlement However, for a constant applied load with negative skin friction from the top, settlement would be about 1.7 inches.

New Zealand – Downdrag Tests

Blast holes around10 m diameter ring(1.2 kg charge @ 4.5 and 8 m)

Piezometers

0.6 m Test Piles

Sondex Tube

CFA Pile Installation

Blast Liquefaction Video

Blast Liquefaction

New Zealand – Downdrag Tests

0

5

10

15

20

25

0 0.5 1 1.5De

pth

(ft)

Unit Side Friction (ksf)

Positive FrictionNegative Friction

References (Piles in Liquefied Sand) ROLLINS, K.M., Gerber, T.M., Lane, J.D. and Ashford. S.A. (2005). “Lateral Resistance of a Full-Scale Pile Group in Liquefied Sand.” J. Geotechnical and Geoenvironmental Engrg., ASCE, Vol. 131, No. 1, p. 115-125. Weaver, T.J., Ashford, S.A. and ROLLINS, K.M. (2005) “Lateral Resistance of a 0.6 m Drilled Shaft in Liquefied Sand.” J. Geotechnical and Geoenvironmental Engrg., ASCE Vol. 131, No. 1, p. 94-102. ROLLINS, K.M., Hales, L.J., Ashford, S.A. and Camp, W.M. III (2005). “P-Y Curves for Large Diameter Shafts in Liquefied Sand from Blast Liquefaction Tests.” Geotechnical Special Publication No. 145, Seismic Performance and Simulation of Pile Foundations in Liquefied and Laterally Spreading Ground, Ed. Boulanger, R.W. and Tokimatsu, K., ASCE, p. 11-23. ROLLINS, K., Bowles, S., Brown, D., Ashford, S, (2007). “Lateral Load Testing of Large Drilled Shafts After Blast-Induced Liquefaction”. Procs. 4th Intl. Conf. on Earthquake Geotechnical Engrg., Springer, Paper 1141 (CD-Rom). ROLLINS, K.M., Bowles, S., Hales, L.J., and Ashford, S.A. (2008). “Static and Dynamic Lateral Load Tests in Liquefied Sand for the Cooper River Bridge, Charleston, South Carolina.” Procs. 6th National Seismic Conference on Bridges, Charleston, South Carolina, Federal Highway Administration, CD-Rom, 12 p.

References (Passive Force) Cole, R.T and ROLLINS, K.M. (2006). “Passive Earth Pressure Mobilization During Cyclic Loading.” J. Geotechnical and Geoenvironmental Engrg., Vol. 132, No. 9, 1154-1164. ROLLINS, K.M. and Cole, R.T. (2006). “Cyclic Lateral Load Behavior of a Pile Cap and Backfill.” J. Geotechnical and Geoenvironmental Engrg., ASCE, Vol. 132, No. 9, 1143-1153. ROLLINS, K.M. and Sparks, A.E. (2002) “Lateral Load Capacity of a Full-Scale Fixed-Head Pile Group.” J. Geotechnical and Geoenvironmental Engineering, ASCE, Vol. 128, No. 9, p. 711-723. ROLLINS, K.M., Sparks, A.E., Peterson, K.T. (2000) “Lateral Load Capacity and Passive Resistance of a Full-Scale Pile Group and Cap.” Transportation Research Record 1736, Transportation Research Board, p. 24-32

References (Downdrag) ROLLINS, K.M. and Strand, S.R. (2006). “Downdrag Forces due to Liquefaction Surrounding a Pile.” Proc. 8th National Conference on Earthquake Engineering, Earthquake Engineering Research Institute, 10 p.

(Come Ski Utah)

Brigham Young University Campus

Downdrag Settlement Procedure 1. Identify liquefiable layer and compute

liquefaction-induced settlement vs. depth profile.

2. Assume a depth to the neutral plane 3. Compute downward force at neutral plane

from axial load plus force from neg. friction 4. Compute upward force from positive friction

and mobilized end-bearing force 5. If in equilibrium you’re ok, otherwise go back

to 2 and revise your assumption.

1. Settlement vs. depth profile

Layer Settlement = εv*Δz

Total Settlement = Σεvi*Δzi

Find Volumetric Strain (Tokimatsu and Seed 1987)

2. Assume depth of neutral plane

N Positive Side

Friction

Negative Side Friction

3. Downward Force P=536 kN (120k)

95 kN (21 k)

Fs = β σ’ As βliq = 0.5βnon-liq

78 kN (18 k)

78 kN (18 k)

4. Upward Force P=536 kN (120k)

95 kN (21 k)

βliq = 0.5βnon-liq

78 kN (18 k)

78 kN (18 k)

18 kN (4 k)

592 kN (133 k) Fs = β σ’ As

Qp (Function of Displacement)

Displacement at Pile Toe

Stoe = Sneut- ΣPavgiΔzi/(AE)pile

Pavg2

Pavg1 Δz1

Δz2

Stoe=35 mm

Toe Resistance

Stoe

Q

Qmax

π (1-ν)QmaxB 4AEs

Where: A = pile cross sectional area Es = soil elastic modulus = 8 N (tsf) B=Pile Diameter, ν= poisson’s ratio

4. Equilibrium P=536 kN (120k)

95 kN (21 k) 78 kN (18 k)

78 kN (18 k) 18 kN (4 k)

592 kN (133 k)

Qp = 177 kN (40 k)

787 kN (177 k)

787 kN (177 k)

OK!

σ = 177k/14.7 in2 = 12 ksi < 50 ksi yield strength

5. Pile Head Settlement Stop = Sneut+ ΣPavgiΔzi/(AE)pile Stop = 45 mm or 1.8 inches

Load Distribution with Constant Load

0

2

4

6

8

10

12

14

16

18

20

22

0 100 200 300 400 500 600 700 800 900 1000

Load in Pile (kN)

Dep

th (m

) Liquefied Zone

Before Liquefaction

After Liquefaction

Liquefied Zone

ralph rollins, performed geotechnical … rollins, performed geotechnical investigations for over...

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