Recent Developments in the Axial, Lateral and Torsional ...Recent Developments in the Axial, Lateral...

Recent Developments in the Axial, Lateral and Torsional Response of Drilled Shaft

Foundations

Armin W. Stuedlein, PhD P.E.Associate Professor

Geotechnical Engineering

Presentation Outline

Motivation and global objectives Project 1: Axial and Lateral Response of Shafts w/ High Strength

Bar and Steel Casing Project 2: Torsional Response of Shafts Axial and Lateral Response Experimental field test program Salient aspects of integrity test results Performance of Shafts to loading Torsional Response Experimental field test program Performance of Shafts to Loading Preview of forthcoming numerical model Summary and conclusions

Motivation and Global Objectives: Project 1Investigation of High Strength Bar and Steel Casing

• Research objectives driven by ODOT Bridge Design Group, with addition of ADSC WCC member firm suggestions

• Main Concern: Seismic. Increased seismic loads necessarily require increased steel reinforcement using current design specifications

• The density of steel in the rebar cage can cause difficulty during concreting, leading to voids and loss of cover

• Objectives:• Evaluate the use of high strength (80 ksi) steel • Evaluate use of permanent steel casing in design for flexure, lateral

load transfer• Evaluate use of hollow bar as dual purpose elements (structural, CSL

access), compare to TIP Thermal Wires

• Axial Load Transfer:• Develop t-z and q-z curves for Willamette Valley soils• Compare t-z and q-z curves between uncased and cased shafts• Compare t-z and q-z curves to FHWA recommendations

• Lateral Load Transfer:• Develop p-y curves for Willamette Valley soils• Compare p-y curves between uncased and cased shafts, and against

typical p-y curves available in commercial software• Compare development and location of plastic hinge across

experimental shafts

Motivation and Global Objectives: Project 1Investigation of High Strength Bar and Steel Casing

• Research objectives driven by ODOT Traffic Structures and Bridge Design Groups – Improve their understanding of torsional load transfer

• For DOTs, torsional loading typically due to:• Wind loading on cantilevered signs• Seismic loading of skewed bridges and flyovers

• Concerned about the lack of design guidance:• Very little full-scale test data exists• NO full-scale load transfer data exist (prior to this work)• No significant assessment of the accuracy of torsional load transfer

models exist• No reliable tools / software for modeling load transfer

available

Motivation and Global Objectives: Project 2Torsional Response of Drilled Shaft Foundations

[ Experimental Field Test Program ]

ShaftDrill

Diameter(in)

Casing Wall

Thickness(in)

Actual Volume of Concrete

(yd3)

Internal and External Steel

(%)

MIR 36 N/a 21.0 2.00

HSIR 36 N/a 20.0 1.50

CIR 36 0.5 17.4 7.20

CNIR 37 0.5 17.3 5.33

Four shafts considered:•MIR: the baseline shaft, constructed with 2% internal steel (60 ksi)

•HSIR: constructed with 1.5% internal steel (80 ksi)

•CIR: cased shaft, 37” OD with 0.5” wall; with 2% internal steel (60 ksi)

•CNIR: cased shaft, 37” OD with 0.5” wall; with 0.15% internal steel (60 ksi); drilled with 37” auger

MIR HSIR

Experimental Field Test ProgramTest Shafts and Experimental Variables

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7

• Compare opening size in reinforcement cage (HSIR in foreground, MIR upper left corner).

• Hollow bar capped at base of shaft.

Experimental Field Test ProgramHSIR: high strength with hollow bar

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8 0 10 20 30 40 50 60 70 80

0

10

20

30

40

50

60

70

80

90

0

5

10

15

20

25

30

Dep

th (f

t)

Dep

th (m

)

Distance (ft)

Stiff to very stiff, silty CLAY to clayey SILT

0 20 40qt (tsf)

Stiff to very stiff, silty CLAY to clayey SILT with a thin SAND lens

Uncased Shafts

Cased ShaftsCPT-1

West, A East, A'CPT-5CPT-3 CPT-4

0 20 40 60 80

0 20 400 20 40 0 20 400 20 40qt (tsf) qt (tsf) qt (tsf) qt (tsf)

?

?

CPT-2Atterberg Limits (%)

Stiff sandy SILT and medium dense silty SAND

with gravel

Subsurface Conditions

Construction: June 2015

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9

Completed Shafts10-month Aging prior to Axial Loading

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10

MIR HSIRCNIR CIR

[ Integrity Tests Results ]

Integrity Tests and ResultsCrosshole Sonic Logging (CSL) Tests

• Advantages:• Widely accepted, standardized• Relatively quick, cheap• High resolution data

• Disadvantages:• Provides indicated in straight-line path

of wave (only)• Need to wait 7 to 10 days, then window

closes after ~21 to 28 days• No indication of concrete cover

thickness / quality

• CSL through hollow bar:• Theoretically should provide no

disadvantage• Threads should improve bond at

concrete/steel interface

Integrity Tests and ResultsCrosshole Sonic Logging (CSL) Tests

• Comparison of the p-wave signal received indicate clear difference in signal quality

• Signal through hollow bar is clear, undamped, regular• Signal through PVC is erratic, muddled• Observations reflected in the “waterfall” plots

-1000

-750

-500

-250

0

250

500

750

1000

0 50 100 150 200 250 300 350 400 450 500

Cros

shol

e Si

gnal

(mill

ivol

ts)

Time (microseconds)

CIR - PVC TubesHSIR - Hollow Bar

Integrity Tests and ResultsThermal Integrity Profiling (TIP) Thermal Wires

• Advantages:• Data captured in 12 to 48 hours following concreting

• Processing time short

• High resolution – measurements on one-foot intervals

• Can produce diameter profile – critical for instrumented shafts and interpreting measured strains

• Less cage congestion – no access tubes

• Disadvantages:• Care is necessary when handling cage – wires may be pinched or cut

• Care is necessary when torching cage stabilizers

• Shorter history with use

• Fewer specialists available with necessary expertise

• Information at base of shaft ??


• Shaft MIR shown here as example

• Time to reach peak heat of hydration: 46 hours

• Shaft diameter consistently larger than 36” auger dia.

• Cage is slightly off-center, as indicated by Wires 3 and 4 (slightly cooler)

• Off-centering ~3/4” max, but concrete cover > 3”


12 15 18 21 24Inferred Shaft Radius (inches)

Rei

nfor

cem

ent C

age

Ground Surface

-10

0

10

20

30

40

50

60

75 100 125 150

Embe

dmen

t Dep

th (f

t)

Mean Temperature (oF)

MIRHSIRCIR

Ground Surface

Dril

led

Sha

ft

(a) (b)

Steel casing

Sonotube

• Near surface temperature differences attributed to “form” used above ground

• Temperature variations in uncased shafts very similar, but indicates definitive differences

• One inch smaller radius for HSIR

• Temperature and inferred shaft radius for CIR indicates gap between soil and shaft

• Implications for load transfer

[ ]Overview of Axial and Lateral Loading Test Results

Axial Loading Tests

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18

Axial Loading Tests: Response at Shaft Head

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0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 100 200 300 400 500

Shaf

t Hea

d D

ispl

acem

ent (

in)

Applied Load, Q (kips = 1,000 lbf)

CIR

CNIR

0.00

0.05

0.10

0.15

0.20

0 250 500 750 1000 1250 1500

Shaf

t Hea

d D

ispl

acem

ent (

in)


MIR

HSIR

Cased Shafts

Uncased Shafts

• Uncased shafts: nearly identical initial response, High-strength Shaft performed better despite having slightly smaller diameter

• 1400 kips at 0.15” • Cased Shafts: significantly

less capacity than uncased• Shaft CNIR was drilled with

37” auger, same as casing OD; Shaft CIR used 36” auger - substantial effect

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 250 500 750 1000 1250 1500

Shaf

t Hea

d D

ispl

acem

ent (

in)


MIR

HSIR

CIR

CNIR

Axial Loading Tests:Load Transfer

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• Significant bending incurred in all four tests

• Load transfer attempted to be corrected for load transfer

• Cased shafts perform in a very stiff, rigid manner

• Effect of construction sequence and gap between casing and borehole apparent

• TIP can be used to identify need for post-grouting remediation

MIR HSIR

CIR CNIR

Axial Loading Tests: t-z response

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21

UNCASED SHAFTS• Mostly hardening-type response

• Auger-induced belling at mid-shaft produced largest response

CASED SHAFTS• Much lower average shaft resistance

• CIR (smaller

MIR HSIR

CIR CNIR

auger) produced peak and softening

Cased Shafts: shallow t-z curves affected by bending and gapping

Lateral Loading Tests: Preliminary Results

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CIR CNIR

MIR HSIR

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• Initial response similar between cased and uncased shafts• Plastic hinge developed at about 200 kips for uncased shafts• Cased shafts perform well to 8”, no indication of hinge• CNIR stiffer

than CIR, surprising…

0

100

200

300

400

0 5 10 15 20

Shea

r For

ce (k

ip)

Applied Lateral Displacement (in)

MIR

HSIR

CIR

CNIR


-10

0

10

20

30

40

50

60

-5 0 5 10 15 20 25

Dep

th (f

t)

Displacement (in)

HSIR @ 45.8 kips

HSIR @ 71.4 kips

HSIR @ 105 kips

HSIR @ 186 kips

HSIR @ 229 kips

HSIR @ 231 kips

Ground Surface

-5 0 5 10 15 20 25Displacement (in)

CNIR @ 48.9 kips

CNIR @ 72.9 kips

CNIR @ 108 kips

CNIR @ 190 kips

CNIR @ 245 kips

CNIR @ 403 kips

Ground Surface


CIR @ 48.9 kips

CIR @ 72.9 kips

CIR @ 108 kips

CIR @ 190 kips

CIR @ 245 kips

CIR @ 403 kips

Ground Surface


MIR @ 45.8 kips

MIR @ 71.4 kips

MIR @ 105 kips

MIR @ 186 kips

MIR @ 229 kips

MIR @ 231 kips

Ground Surface

April 23, 2017

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• Lateral deflection profiles near-finalized• p-y curves not yet developed, will be generated using strain gages

and lateral deflection profiles • Cased shafts are significantly stiffer, HSIR stiffer than the baseline

shaft MIR; CNIR stiffer than CIR

MIRHSIR CIR CNIRDefinitive Hinge at

3.5D Point of bending at 8.5D

Also at 8.5D

Definitive Hinge at

3.5D

2.9” 2.7” 2.5” 2.0”9.7” 18.4” 3.6” 3.1”


[ ]Project 2: Torsional Response of Drilled Shafts

Motivation for Work

• In the Pacific Northwest, wind speeds are not trivial

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• December 2014: Peak gusts of 144 km/hr

• October 1934: Peak gusts of 145 km/hr

• October 1962: Peak gusts of 258 km/hr

In Kansas, Max wind gust speed recorded July 11, 1993: 162 km/hr, not trivial

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Experimental Program: Subsurface Conditions

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7 8 9 10 11 12

Dep

th (m

)

0 20 400 20 40 0 20 40 0 8 16 24qt (MPa) SPT-Nqt (MPa) qt (MPa)

??

? ? ?

?Sand to

Silty Sand

stiff to very stiff, Silty Clay to Clayey Silt

medium dense, Sand to Silty

Sand

Distance (m)

EDS

TDS TDSFB

CPT-3 CPT-1CPT-2 B-2014-1Southwest, A Northeast, A'

?

B-2014-2

0 50 100Water Content and Atterberg

Does the silty sand layer (Dr = 75% and ~1m thick) contribute significant torsional resistance?

Experimental Program: Test Shafts

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28

• Design signal pole and pole structure: SM3 (ODOT Standard Dwgs. TM651, TM653)• Design axial load: 4.75 kN• Shear: 10.5 kN• Moment: 187.6 kN-m• Torque: 112.4 kN-m

• ODOT design procedure: Using Broms (1964), in consideration of lateral resistance (only), choose shaft length that provides FS = 2.15

• Torsion not considered directly… (??!!)

Experimental Program: Loading Tests

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Quasi-Static Loading

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[ ]

Experimental Program: Quasi-Static

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TDS

TDSFBApplied Rotation at Head vs. Developed Torque

0

50

100

150

200

0 2 4 6 8 10 12 14

Torq

ue, T

(kN

-m)

Rotation, θ (deg)

TDS

TDSFB

0

50

100

150

200

250

0.0 0.5 1.0 1.5 2.0

Torq

ue, T

(kN

-m)

Rotation, θ (deg)

TDSFB: MeasuredTDS: MeasuredTDS: Extrapolated


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Torsional shear strain profiles: with depth

0.9 1.0 1.1 1.2 1.3 1.4-1

0

1

2

3

40 10 20 30 40 50

Diameter, D (m)D

epth

(m)

Absolute Shear Strain, ε45°(microstrain)

0.021° 0.048°0.071° 0.086°0.092° 0.103°

D

0.9 1.0 1.1 1.2 1.3 1.4

0 10 20 30 40 50

Diameter, D (m)

Absolute Shear Strain, ε45°(microstrain)

0.02° 0.08°0.24° 0.51°1.07° 1.75°

(b)

D

50+ Unreliable Gages

TDS TDSFB


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Torsional Load Transfer Observed over Tributary Areas: with Depth

0 7 14 21

-1

0

1

2

3

4

5

0 50 100 150 200 250 300

qt (MPa)

Dep

th (m

)

Torque (kN-m)

Ground Surface

Unreliable Gages

CPT

TDS TDSFB


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Torsional Load Transfer Observed over Tributary Areas: with Rotation

0

30

60

90

120

Uni

t Sha

ft R

esis

tanc

e, τ

(kPa

) 0 to 0.18 m 0.18 to 1.1 m1.1 to 2.1 m 2.1 to 3.1 m3.1 to 4.1 m Extrapolated

(c)

0

30

60

90

120

0.0 0.5 1.0 1.5 2.0

Uni

t Sha

ft R

esis

tanc

e, τ

(kPa

)

Rotation, θ (deg)

0 to 0.18 m 0.18 to 1.1 m1.1 to 2.1 m 2.1 to 3.1 m3.1 to 4.0 m

(d)

0.08

5E-4

)

)

Shaft in SAND

Shaft in Clayey SILT

All of shaft in Clayey SILT

TDS

TDSFBU

nitS

haft

Res

ista

nce

(kPa

)

θ/rs = 1.08E-4θ + 2.45E-4

R² = 0.991

θ/rs = 1.82E-2θ + 2.54E-4

R² = 0.981

0.0E+0

4.0E-4

8.0E-4

1.2E-3

1.6E-3

θ/τ

Observed from 3.1 to 4.1 mObserved from 2.1 to 3.1 mOmitted

(a)

Uni

tSha

ftR

esis

tanc

e(k

Pa)

0

10

20

30

40

50

60

70

0.00 0.02 0.04 0.06 0.08

Uni

t Sha

ft R

esis

tanc

e, τ

(kPa

)

Rotation, θ (deg)

Observed from 3.1 to 4.1 m

Observed from 2.1 to 3.1 m

Hyperbolic Fit

(b)

Hyperbolic Model Fitting (TDS)

ba

bars

Skipping the summary…but thanks to colleagues

and the Sponsors!

April 23, 2017

35

[ ]Colleagues• Prof. Andre Barbosa• Qiang Li, OSU PhD Student

Recent Developments in the Axial, Lateral and Torsional ...Recent Developments in the Axial, Lateral...

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