ralph rollins, performed geotechnical … rollins, performed geotechnical investigations for over...
Post on 16-Mar-2018
216 Views
Preview:
TRANSCRIPT
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%)
Computed (Pd=9, Ru=95%)
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
)
Charleston (8.3 m, Ru=81%)
Computed (Pd=9, Ru=95%)
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
)
Charleston (10.1 m, Ru=69%)
Computed (Pd=9, Ru=95%)
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=??)
Computed (Pd=9, Ru=95%)
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
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 = 2950 kN
-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 = 3950 kN
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
Schematic View of Behavior
Fs= βσ´As
Immediately After Liquefaction
Δu = σ´ β = 0 relative to σ´
≈ 0 o
o
Schematic View of Behavior
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 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
top related