bullock bidirectional testing

www.fugro.comwww.loadtest.com

Deep Foundation Uncertainty and Bi-Directional Static Load

TestingPaul J. Bullock, PhD

Fugro Consultants Inc.Loadtest


Deep Foundations

Precast Concrete

H-pile

Cast-in-Place

Pipe

Timber


Which Deep Foundation Type?

• Type of Load (axial, lateral, torsion)

• Magnitude of Load• Project Size & Complexity• Site Conditions• Environmental Conditions• Local Availability & Price• Familiarity (engineer, client) & complacency• Foundation Cost Controlled by Uncertainty

(conservative design plus safety factor)

EngineeringDecisions


Deep Foundation Design Uncertainty

• Site Variability• Axial, lateral, depth to bearing stratum• Strength, stiffness, test quality• Typically test < 0.01% of site

• Design Method: RN = Rside + Rbase

• Calibration, empiricism, codes, resistance or safety factors based on uncertainty

• Construction Quality• Contractor experience• Quality of supervision


Reduce Cost by Reducing Uncertainty:

• Informed design (integrated investigation: geophysics + insitu testing + sampling)

• Design verification (static & dynamic testing)• Optimization (redesign)

• reduce length, size, number• change type (driven, drilled, anchor)• reduce cost and construction time ($$)• FLT’s experience - savings 5X test cost

• Quality control testing to assure performance & reduce remediation cost


Integrated Ground Investigation

• Measure ground properties for design• More time characterizing site → more reliable design• Staged approach - progressively more targeted• Geophysical techniques provide overview • Insitu testing (CPT/DMT) calibrates geophysics, reduces

sampling disturbance and laboratory testing uncertainty• Insitu profiling (CPT) identifies thin layers missed by

drilling and sampling program• SPT not so great (drilling disturbance, variable energy)• Sampling and testing to characterize problem zones• Does not have to cost more, and can cost less• Preliminary pile tests included to prepare better plans?


Horizontal Distance, m

Dep

th, m

Sand

Silty Clay

ClayeySand

Sounding Stopped at 33.5 m

Silty Clay

ClayeySand

0 2010CPT 03 qc, MPa

0

5

10

15

20

Sand

Clay

SiltyClay

Sand

ClayeySand

Refusal

0 2010CPT 01 qc, MPa

Dept

h, m

Tim

e, n

s

CPT 01

CPT 03

GPR Example

UF Insitu Test Site


ElectroresistivityElectrical Resistivity Tomography Profile


Electromagnetic ConductivityElectromagnetic Conductivity Profile


Sand Overburden

Weathered Bedrock

More Competent

Bedrock

Bedrock Mapping

Seismic Refraction Tomography


Insitu Cone Penetrometer Test (CPT)

• Robust push-in tool (ASTM D5778)

• Profiles penetration resistance

• Estimates soil type

• Undrained shear strength (clay)

• Friction angle (granular soils)

• Footing settlement, bearing pressure, pile capacity

• Compaction quality control

• Depth to cavities or bearing stratum

• Optimize borehole program


CPT Platforms


CPT Measurements / Soil Type


Marchetti DilatometerPush-in Flat Blade

Minimizes Penetration Disturbance

(ASTM D6635)

Measurements:• Insitu Lateral

Stress• Modulus• Shear Strength• Depth Profile

(every 20 to 30 cm)Drill Rig

CPT Rig


Marchetti DilatometerUses:• Settlement• Slope Stability• Lateral Stress

(walls, tunnels, excavations)

• Compaction Control• Dissipation Testing,

cH


Top-down Static Load Test (ASTM D1143)

Design Optimization requires load to failure plus instrumentation


Kentledge CollapseDue to platform/ground failure

from FPS Load Testing Handbook 2006


Reaction Beam CollapseDue to tension bar failure

from FPS Load Testing Handbook 2006


Bi-Directional Osterberg Cell Testing• Specialized jack in pile uses

bearing to mobilize side shear

• Developed by Dr. Jorj Osterberg and AEFC

• LOADTEST Inc. founded 1991 (purchased by Fugro in 2008)

• First “O-cell” tests on driven steel pipe piles 1987

• >2000 O-cell tests to date, mostly drilled shafts (300+/yr)

• ~ 30 driven piles since 1987 (12”-66”, 52 tons – 1,480 tons)


P = F+Q

Conventional Test

F

Q

F

F1

Q

F2

Q

Osterberg Cell Test

O = F = Q = P/2 O = F1 = (F2+Q)

O

O

Pile Provides Reaction

Reaction System

P


O-cell Features

• Robust for installation

• Aligned with pile axis

• Special seal for eccentricity

• Water used for hydraulic fluid

• Rated at 10,000 psi

• Calibrated by AEFC (NIST Traceability)

• Linear & Repeatable

• Strain gauges also confirm load

24” PHC Korea


O-cell Instrumentation

• O-cell Pressure monitored by gauge and transducer

• Pile Top Movement

• O-cell Expansion Transducers

• O-cell Top Telltales

• Pile Bottom Telltales

• Embedded Strain Gauges

• Embedded Pile Compression Transducers


Pumps

Drilled Shaft O-cell Test Setup

The contractor can demobilize, saving time and money


Typ. O-cell Test – No Reference Beams

Leica digital levels monitor targets on top of shaft directly.Accuracy actually improved (Sinnreich, Simpson, DFI Journal, 2009).


Driven Pile O-cell Test Setup• ASTM D1143

Quick Test (new standard coming)

• 20 Loads to failure

• 8 min load intervals (identify creep limit)

• All instruments monitored by datalogger

• Real-time load vs. deflection plot

• Reference beams replaced by electronic levels


Load Transfer from O-cell & Strain Gauges

+465

+475

+485

+495

+505

+515

+525

+535

+545

+555

+565

+575

0 500 1,000 1,500 2,000 2,500

Elev

atio

n (

ft )

O-cell Load ( kips )

Top of Shaft

Bottom of Shaft

1L-1 1L-3 1L-5 1L-7 1L-9

S. G. Level 6

S. G. Level 5

S. G. Level 2

S. G. Level 3

O-cell Load

1L-11 1L-13 1L-171L-15 1L-19


Side Shear from Load Transfer

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0 0.5 1.0 1.5 2.0 2.5

Mob

ilize

d N

et U

nit S

ide

Shea

r ( k

sf )

Upward Average Shear Zone Displacement ( in )

S.G. Level 6 to Zero ShearS.G. Level 5 to S.G. Level 6S.G. Level 3 to S.G. Level 5S.G. Level 2 to S.G. Level 3O-cell to S.G. Level 2


O-cell SizesO-cell Size Rated Capacity Max. Test Load

6” 100 tons 200 tons

9” 225 tons 450 tons

13” 438 tons 875 tons

16” 700 tons 1400 tons

20” 1125 tons 2250 tons

24” 1550 tons 3100 tons

26” 1950 tons 3900 tons

34” 3000 tons 6000 tons

• Cells typically welded to load plates• Cells can be grouped together• 6” stroke standard, 9” stroke available


Drilled Shaft O-cell Plate Assembly

Weld Top and Bottom Plates to the O-cell

Weld O-cell Assembly to Rebar Cage


Lifting the Cage and O-cell Assembly

Attach O-cell to Cage, lift carefully, place in shaft excavation


Attaching O-cells to bottom plate

Multiple O-cell Assemblies


Multiple O-cell Assemblies

Attaching O-cells to top plate


Other O-cell Assemblies

O-cells placed at 2 levels to isolate distinct shaft elements

Rebar cage not required (save money and time)


O-cells in CFA / ACIP Piles


Maximum size/loads tested to date

Pile Diameter, mm 600 750 900 900

Pile Length, m 38 40 35 36

O-cell Diameter, mm 405 540 660 2x540

Mobilized Load, MN 17.5 32 32 46

O-cells in CFA / ACIP Piles


Las Vegas

O-cells in Barrettes


Alfaro’s Peak, Manila, Philippines

O-cells in Barrettes


Barrettes - St. Petersburg, Russia

• 60 m deep

• 90 MN capacity


O-cells in Driven PilesO-cell cast into or welded

to pile before drivingO-cell grouted into pile

after driving

66” Cylinder Pile, Harrison County, MS30” PSC Pile, Morgan City, LA


Example: 18” Steel Pipe Piles, MASaugus River Bridge Pines River Bridge• Delmag

D62-22• Refusal

10 blows per 0.5”

• 142 tons O-cell Load

• 0.28 tsf Side Resistance Failure (0.3”)

• 80 tsfEnd Bearing (not failed)

• 284 tons Capacity

• DelmagD36-13

• Refusal 10 blows per 0.5”

• 215 tons O-cell Load

• 0.39 tsf Side Resistance Failure (0.3”)

• 122 tsfEnd Bearing (not failed)

• 430 tons Capacity


FL Research Pile Setup

• Five 18” PSC Piles• PDA Tests• Long-term, staged

static tests (25)• Osterberg Cell in tip• Strain Gages• Telltales• Piezometers• DMT Stress Cells Osterberg Cell

Cast Into Pile,with XXS Pressure Pipe to Top

PileSideShear

Pile End Bearing

O-cell® TopTelltales Inside PVC Pipe

O-cell® Bottom Telltale (through center of pressure pipe)

Friction Collarfor Gage Support O-cell®

Tee

(not to scale)

Dilatometer Cell (L)& VW Piezometer (R)on Pile Face

VW Strain Gage(in pairs, tied to prestress strands)

Hydraulic Pumpwith Gage& Piezometer

Wireline & Scale


FL Research Pile Setup: O-cell


0 50 100 150 200 250 3000

500

1000

1500

2000

2500

Aucilla, Static TestAucilla, Dynamic Test

1 min

15 min

60 min

1727 days

Elapsed Time, t (days)

Pile

Sid

e Sh

ear

QS

(kN

)

Bullock et al. (1995) in FL18” PSC, O-cell at bottom

FL Research Pile Setup – Arithmetic Plot

= 225 tons


0.001 0.01 0.1 1 10 100 10000

500

1000

1500

2000

2500

Aucilla, Static TestAucilla, Dynamic Test

1 min

15 min

60 min

QS0 =1021 kN (at t0 = 1day )

mS = 293.4 kN

Elapsed Time, t (days)

Pile

Sid

e Sh

ear

QS

(kN

)


(EOID Capacity plotted at 1 min)

FL Research Pile Setup – Log-linear Plot

= 225 tons


where: A = Dimensionless setup factorQS = Side shear capacity at time tQS0 = Side shear capacity at reference time t0fS = Unit side shear capacity at time tfS0 = Unit side shear capacity at reference time t0t = Time elapsed since EOD, dayst0 = Reference time, recommended to use 1 daymS = Semilog-linear slope of QS vs. log t

Note: “A” is correlated to soil type (0.1 to 0.8) anddescribes the capacity increase per log cycle of time (relative to the reference capacity)

1log1log00000

tt

Qm

ttA

ff

QQ

S

S

S

S

S

S

Non-dimensional side shear setup:


0.001 0.01 0.1 1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2Aucilla, Dynamic Test

Aucilla, Static Test

A = (mS / QS0) = 0.30R2 = 0.99

1 min

15 min

60 min

Elapsed Time Ratio, ( t / t0 ) with t0 = 1 day

Pile

Sid

e Sh

ear

Rat

io, (

Qs /

Qs0

)


+30%

+30%

+30%

Σ = +90% in 1 day(or 9X 1 min capacity)

1-3d+14 %

1-7d+25%

1-28d +43% orabout half ofEOD-1d change

FL Research Pile – Non-dimensional Plot


Example: Morgan City, LA - 30” PSC• HPSI 2500, 300 bpf• 30” PSC, 18” Void, 143 ft long• Pile Setup Clay/Sand• 950 ton O-cell

369 tons at 1wk

416 tons at 3 wks

464 tons at 5 wksMax. O-cell Load 493 tons

Buoyant Pile Weight 29 tons


Example: Busan, Korea - 24” PHC• Prestressed Spun High Strength Conc.• 24” OD, 16” ID, 103 ft long, 46 ft sections• Sand / Clay / Sand• 875 ton O-cell, 7 Strain Levels, Grouted

Buoyant Pile Weight 16 tons Max. Side Shear 456 tons

Unit Side Shear 0.14 to 1.98 tsf

Max. O-cell Load 472 tons (944 ton test)

Max. End Bearing 155 tsf


Example: Harrison County, MS - 66” Cylinder

• Conmaco 300, 128 bpf EOID• 66” OD, 54” ID, 108 ft long• Silt / Sand / Dense Sand• 3000 ton O-cell, 4 Strain Levels

Buoyant Pile Weight 114 tons Max. Side Shear 626 tons

Unit Side Shear 0.23 to 4.10 tsf

Max. End Bearing 45 tsf

Max. O-cell Load 740 tons (1480 ton test)


O-cell Tests World-Wide

1-1011-2021-30>30

0

Upcoming/In progress

Key


Carquinez Bridge, Vallejo, CA Benicia-Martinez Bridge

O-cell Application: Bridges

Sheik Zayed Bridge, UAE My Thuan Bridge, Vietnam


Cooper River, SC Jiangsu Sutong, China

O-cell Application: Bridges

Confederation, PEI/NB Panama 2nd Bridge


O-cell Applications: Buildings

Venetian Hoteland Casino,

Las Vegas, NV

One Raffles Quay,

Singapore

Four Seasons Hotel Miami, FL


O-cell Applications: Buildings UAE

23 Marina Tower Al Rafi Towers

Infinity Tower


• Test drilled shafts (wet/dry), CFA piles, driven concrete or steel piles, barrettes

• Separates side shear & end bearing• Very high load capability (321MN, St. Louis)• Direct loading of rock socket• Cost, safety, and space advantages• No additional reaction system needed• Doubles effective jack load• Post-test grouting for production piles

O-cell Static Load Test Advantages


Efficient O-cell Test Applications

• End bearing side resistance (use ultimate!)• Restricted site access (remote location, existing

structures, environmentally sensitive, water)• Prove capacity distribution (end bearing vs. side

resistance, unit side resistance)• Accelerated construction schedule• Large test loads required• Site safety restrictions (personnel & equipment)• Repeated tests (setup)• Multiple test piles (but only one test frame)• Compare with total cost of conventional testing


• Pile preselected for testing• Maximum load limited by the weaker of the

end bearing or side shear (add top load?)• Top of pile not structurally tested • Subtract buoyant weight of pile above O-cell

to calculate side resistance• Must construct equivalent top load

movement curve• use the sum of measured behavior• use the sum of modeled behavior• use finite element or t-z approach

O-cell Test Limitations


Typical O-cell Test Result

(1 MN = 112.4 tons)

2,700 tons


Equivalent Top-Load Curve


Equiv. Top-Load + Elastic Shortening





• reduce length, size, number• change type (driven, drilled, anchor)• reduce cost and construction time ($$)• FLT’s experience - savings >5X test cost

• Quality control testing to reduce cost of post-construction remediation


25 4445

46

9574

123

94

75

25

109 88

89

40

28 29

127

128

105

104

35

37

31

M/E=25

106

38

Ratio of Measured / Estimated Capacity

128 = LOADTEST Project Reference no.

Schmertmann &Hayes

M/E

1

5

10

15

Soft to Hard Soils Intermediate Hard Rock

One of FLT’s first major discoveries! (How designers handle uncertainty

i.e. lower expectations lead to higher costs)


25 4445

46

9574

123

94

75

25

109 88

89

40

28 29

127

128

105

104

35

37

31

M/E=25

106

38

1

5

10

15

Wasted value due to uncertainty and complacency

Ratio of Measured / Estimated Capacity

M/E

Soft to Hard Soils Intermediate Hard Rock

One of FLT’s first major discoveries! (How designers handle uncertainty

i.e. lower expectations lead to higher costs)


Initial Design• 9 m Rock Sockets (“typical”)• Design side shear: 1.3 MPa (code)

O-cell Tests• 2 Shafts with 1.5 m rock sockets• Measured side shear: 2.7 MPaEstimated vs. Actual Costs• Final design: 4.5 m rock sockets• Design FS = 3, Measured FS > 5• Redesign FS > 2• Fdn. Cost Est.: $18,000,000• Testing cost: $ 255,000 • Fdn. redesign cost: $ 8,900,000• Net Savings: $ 8,845,000

Cost Savings: Seacaucus NJ Transfer Station


Job Number 566 775 835 381 056* 335 426 635

State CA FL NC NJ SC GA TX FL

Fdn. Estimate $850 $6,200 $32,500 $18,000 $160,000 $3,270 $8,500 $4,520

Fdn. Redesign $610 $4,980 $24,500 $8,900 $125,000 $3,003 $8,500 $7,232

Savings $240 $1,220 $8,000 $9,100 $35,000 $273 $0 -$2,712

Test Cost $79 $360 $2,000 $255 $7,500 $240 $95 $305

Net Savings $161 $855 $6,000 $8,845 $27,500 $33 -$95 -$3,017

Calculated FS 2.5 3.0 3.0 3.0 3.0 3.0 3.0 2.5

Measured FS 3.0 3.5 4.0 5.0 NA 3.5 9.5 0.8

Redesign FS 2.0 2.0 2.0 2.0 2.0 2.3 9.5 2.0

Foundation Savings After Testing Based On Actual Jobs Completed (Thousands)

• More than 70% of the FLT testing saved the client money• Half of the remaining 30%, testing done too late to realize the savings• Only a few estimates were so close not to allow a modified foundation

O-cell Tests Result in Project Cost Savings


Deep Foundation Quality Control• Driven Piles

• Blow Count, Hammer Energy, Dynamic Tests• Drilled Shafts

• Control Slurry Properties• Prepare Excavation Log• Shaft Profile - Sonic Caliper• Clean Shaft Bottom

– MiniSID, Downhole Camera• Concrete Quality - Pile Integrity Test,

Crosshole Sonic Logging, Thermal, Gamma• Verify Pile Capacity using RIM-cell


Shaft Profile - SONICALIPER


Uses sound reflection360°profile of shaft wallsChecks hole verticality and driftReal-time results6 mm Accuracy, 3-D modelingPortable and compactMinimal impact to schedule

Shaft Profile - SONICALIPER


• Verticality• Cage Encroachment• Calculate Concrete

Volume

Shaft Profile Report - SONICALIPER


Shaft Volume - SONICALIPER


• RIM-cell pressurizes pile cross-section• Full-scale static bi-directional load test• Install a RIM-cell in any pile• Economical testing• QA/QC device eliminates uncertainty• End-bearing engaged during test,

stiffens shaft response under load

RIM-CELL

60” RIM-cell


Cross-section of a RIM-cell installed at the shaft toe.

RIM-CELLTESTING


The RIM-cell confines the fluid pressure, creating a hydraulic cylinder at the shaft toe capable of applying high static loads.

RIM-CELLTESTING


Fluid grout is pumped through the hydraulic hoses creating a fracture across the shaft, pressurized within the RIM-cell.

RIM-CELLTESTING


As the internal grout sets, more grout is pumped into external pipes to fill the annular fracture around the RIM-cell.

RIM-CELLTESTING


RIM-CELL Applications• PROOF TEST

• Install in every pile• Load shafts to design load or

higher (2000 – 5000 psi)• Eliminate uncertainty of site

variability• Use higher LRFD factors• Detect / remediate a “soft toe”

• POST-STRESSING• Consolidate loose material at

shaft toe• Engage end bearing without

losing side shear• Limit settlement at service load


RIM-CELL AssemblyRIM-cell fits inside reinforcing cage. Hydraulic hoses and instrumentation

pipe installed on cage. Add strain gages to isolate different soil strata.

RIM-cell welded to frame below O-cell assembly for a

multi-level test shaft.

24” RIM-cell installed with 8 levels of strain gages

60” RIM-cell


Excavate shaft and place cage with RIM-cell. Large center opening allows tremie pipe to pass. Low

cross-sectional area does not inhibit concrete flow or trap weak material.

RIM-CELL Installation

60” RIM-cell installed into 78” rock socket

24” RIM-cell at toe of an O-cell test shaft

20” RIM-cell installed at the toe of 30” shaft


Perform test after concrete obtains strength. Cement grout is mixed and pumped through the hydraulic hoses into the RIM-cell. Measured pressure is converted to load using calibration factor of the RIM-cell. Load is increased to 1.2 to 1.5 times design load. Shaft movement is measured and recorded. Grout will set up to restore integrity to the shaft.

24” RIM-cell Test Curve 36” RIM-cell Test Curve

RIM-CELL Testing


Similar to O-cell with real-time Load-Displacement plot during

test. Preliminary results available same day as test.

RIM-CELL Reporting

60” RIM-cell

Schematic section of RIM-cell

shaft

Equivalent Top Load Plot


RIM-CELL Limitations

• Internal friction unknown (but small)• Preselect shaft

(install in every shaft, test as required)• Reduced pressure vs. O-cell

(but large area)• Typically will not test to failure• Grouting required to restore shaft integrity• Maximum load limited by the weaker of the

end bearing or side shear (add top load?)• Top of pile not structurally tested


Missouri Research Project

• 24” bi-directional test piles on two different sites

• Two piles on each site were tested using RIM-cells

• 24” RIM-cells in 36” piles• 20-30 feet deep shafts in

unweathered and weathered shale

• Side by side comparison to O-cell tests

24” (600mm) RIM-CELL Tests


24” RIM-CELL Tests

Similar piles on same site. O-cell test (red) mobilizes ultimate capacity. RIM-cell test (blue) confirms design load.


RIM-CELL Tests to DateRIM‐cell Size Shaft Diameter Max

PressureMax Cell Load Test Result

14" 24" 2500 psi 350 kips Side Shear Failure

14" 24" 1780 psi 250 kips End Bearing Failure



24" 36" 2560 psi 1100 kips RIM‐cell Capacity Maxed Out

24" 36" 1980 psi 850 kips RIM‐cell Capacity Maxed Out



24" 30" 940 psi 400 kips Test stopped at 1" Expansion


60"96"

(76"rock socket) 4950 psi 13,000 kips Test stopped at 1/2" Expansion


Summary• O-cell test proven for shafts and driven piles• Compare overall cost and quality of test

results for conventional top-down testing with O-cell testing

• RIM-CELL tests to verify production pile capacity (QA/QC)

• Coming Attractions:• New ASTM Standard• Bigger piles, higher loads• Mid-pile O-cell placement for spliced

concrete piles• Mid-pile placement for steel pipe piles


Summary

• Deep foundation design generally conservative due to uncertainty.

• Correlate site characterization with foundation design and testing. Reduce project cost through more efficient design and construction. Reduce uncertainty.

• Use a portion of the cost savings to fund the testing and inspection needed for more efficient design.

“The owner pays for a good site investigation whether he does one or not.”


Thank You

www.loadtest.comwww.fugro.com

bullock bidirectional testing

Engineering

test quality

deep foundation uncertainty

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site design method

deep foundation type

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