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… Axial Load Testing for Pile Design

Kyle Rollins Brigham Young University

One good test is worth a thousand expert opinions.

Werner Von Braun Designer of Saturn V Moon Rocket Space Shuttle Columbia Disaster

Analyses based on impact of small ice particles imply styrofoam impact won’t be a problem.

Full-scale test shows a problem! Healthy Skepticism for Tests . A theory is something nobody believes, except the person who proposed it. . An experiment (test) is something everybody believes, except the person who performed it --Albert Einstein

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

--Abraham Lincoln Pile Load Testing Desirable for: . Projects with large number or piles, small improvements yield large cost savings.

Pile Groups for Bridges on I-15 World’s Largest Solar Power Plant-Ivanpah, California 400 MegaWatt- 153,000 Support Piles for Solar Reflectors

Pile Load Testing Desirable for: . Projects with large number or piles, small improvements yield large cost savings. . Increased reliability for unfamiliar soils or new pile types. . Critical structures with significant loss due to pile failure. . Lower factor of safety (Higher Resistance Factor) . Research to improve design equations . Pile setup may be important

Pile Set-up Behavior on I-15 Pile Load Testing Desirable for: . Projects with large number or piles, small improvements yield large cost savings. . Increased reliability for unfamiliar soils or new pile types. . Critical structures with significant loss due to pile failure. . Lower factor of safety (Higher Resistance Factor) . Research to improve design equations . Pile setup may be important

Axial Static Load Tests

. Conventional Static Jacking Tests . Statnamic Testing (Rapid Load Testing) . Osterberg Cell Testing Static Jacking Tests

Courtesy Dan Brown Conventional Static Tests

. Test Setup - Equipment and Measurements . Instrumentation . Loading & Interpretation . Advantages & Limitations Test Setup

. Reaction System . Loading & Load Measurement . Reference System & Displacement Measurements Static Vertical Load Test Setup Reaction beam Static Load TestsStiffeners

Plate Load cell Spherical bearing Ram Hydraulic jack Bourdon Gage LVDT Dial Gage Stem reaction Bracket attached plate to pile Mirror Scale Wire Grade

Test Pile Kentledge (Dead Wt.) System Reaction Pile System–Vancouver, BC

400 ton Frame for Liquefaction Downdrag Test Reaction Pile System  Up to 600 tons pretty common  Up to 1200 tons reasonable, 4000 tons possible.  Care in alignment!  Spacing (>6D ASTM, >3.5D Reese & O’Neill)  Design by licensed civil engineer BYU/UDOT Load Frame

. 1200 Ton Capacity . Used for I-15 project to test to failure AMEC Load Frame

. Mobile Arrangement . 1000 Ton Capacity Caltrans’ $1 Million Load Frame

64 ft long, 9.3 ft high, 6 ft wide . World’s largest reaction frame (4000 tons) . Expected to save $6 to $10 million per year on construction costs Load Test on Santa Clara River Bridge on I-5 in N. Los Angeles

$14 million cost saving Loading

. Calibrated hydraulic jack . Calibrated load cell w/ bearings . Avoid misalignment! Loading Procedures

. Quick load test method (most common in US)  Load applied incrementally (10%) and held for constant 2.5 to 15 minute period. . Slow Maintained test method  Load applied in 25% increments to 200% of design load  Each load held 2 hrs. min. and until δ/t < 0.002 in/min . Constant Rate of Penetration  0.01 to 0.05 in/min for clay; 0.03 to 0.10 in/min for sand Reference System

. Reference Beam Stability & Supports . Redundancy! . LVDT or Linear Pots w/ data acquisition system . Dial Gauges . Optical measurements (scale & mirror w/ piano wire) . Surveying instruments Rapid Load Testing Statnamic Testing

load displacement

load strain displacement acceleration

14 Load Test Type Definitions

. Static Test – Duration, T > 1000 L/c . Dynamic Test – Duration, T < 10 L/c . Rapid Test - 10 L/c < T < 1000 L/c  Typical Axial Statnamic Duration 100 to 120 msec Schematic of Vertical Statnamic Test

Exhaust Vent/Silencer Reaction Weights Load Piston Combustion Chamber

Load Cell and Laser Window 5000 Ton Gravel Backfill Device

2000 Ton Hydraulic Catch Device Statnamic Test Firings

30 MN (6750 kip) Device within Gravel Filled Cylinder

Courtesy of Applied Foundation Testing, Green Coral Spring, Florida 14 MN (3100 kip) Device with Hydraulic Catch Mechanism 1000 Ton Statnamic in Utah Instrumentation

RAPID LOADING APPARATUS

LOAD CELL STATIONARY REFERENCE

DISPLACEMENT TRANSDUCER

ACCELEROMETER

PILE FOUNDATION

SIGNAL CONDITIONING

STORAGE AND DISPLAY Load Cell Calibrated Full Scale

Laser Displacement Sensor Laser Projector Capacitive Accelerometers Force & Settlement Time Histories

-0.40 800

-0.30 600

-0.20 Displacement 400 Force -0.10 200

0.00 0

0.10 -200 (kips) Force Settlement (in) Settlement

0.20 -400

0.30 -600 0.0000 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.40 -800

Time (sec) Unloading Point Method Model-Axial Loads

Stanamic Force, (Fstn)

Pile Mass, M (Fa) Fstn = Fu + Fv + Fa or Sping, K Dashpot, C (Fv) F = F - F - F (Fu) u stn v a

Fu = Fstn - Cv - Ma Unloading Point Analysis Procedure

3000 Maximum Fstn 1. Pick Fstn where v=0. 2500

2000 2. (Fu)max = Fstn - Ma 1500 (F ) -Ma-(F ) Force, kN stn max u max 1000 3. C = F @ v=0 stn v 500 4. F = F - Cv - Ma 0 u stn 0 5 10 15 20 25 30 Deflection, mm Statnamic Results

Load (lbs) 0 100,000 200,000 300,000 400,000 0.0 0.1 Statnamic Interpreted Static 0.2 0.3

0.4 Deflection (in) Deflection 0.5 0.6 Segmental Unloading Point Method

. Method for long shafts, utilizing strain gauge or embedded accelerometer data

F1meas. FStatnamic

Gage Nw = 5 Level 1

Cv skin. m2 kx skin.

Strain Gage Gage Level 2 Levels

F2meas. Static versus…

Statnamic… 1900 Ton Statnamic Test of 54” Cylinder Pile (self supported by pile 32 feet above water).

Courtesy Dan Brown Load Rate Tests in Salt Lake City, Utah

SML QML 16 hrs. 50 min. 2 min. 20 sec. Statnamic Effect of Loading Rate on Pile Capacity

2.5

2

1.5

1

0.5 Failure Load/(54 Minute Load/(54 Failure Load) Failure

0 0.0001 0.0010 0.0100 0.1000 1.0000 10.0000 100.0000 Velocity, v (mm/sec) Allowance for Rate of Loading Effects

Strain Rate Reduction factors for Axial Load (Mullins et al, 2002)  0.95 for Rock  0.91 for Sand  0.69 for Silt  0.65 for Clay Factor of 0.55 for SLC tests in Clay

Rate Effect Corrections in Clay Weaver and Rollins, ASCE JGGE Oct. 2009

Avg. Rate Reduction Factor = 0.47 Advantages of Statnamic Testing

. Large load capacity, applied at top of pile . Reaction system not needed . Economies of scale for multiple tests . Useful for proof testing on production piles . Can mobilize large toe displacements . Long wave length Limitations

. Capacity high, but still limited . Rapid loading method: rate effects are significant in clay soils . Mobilization costs for reaction weights Fundex PLT Capability

. Mobile testing unit capable of 6 to 10 compression tests/day . Up to 800 kips load capability . Self-sufficient unit

Fundex PLT Operation

. 25,000 kg weight dropped from progressively increasing heights . Heavy coiled springs diffuse impact and spread energy over a 200 ms period . Weight is hydraulically caught on upward stroke to allow only a single blow . Deflection is recorded by optical receiver from LED transmitter fastened to test pile. . Load measured by load cell above pile. . Family of individual drops is compiled to create classical Load Deflection Curve. Hydraulic Clamp

25,000 kg Weight

Damping Springs

Receiver Load Cell LEDs

Test Pile DATA AQUISISION SYSTEM

Displacement Measurement System Load Cell LED Transmitter Fundex Pile Load Tester

Courtesy of American Pile Driving, Inc. Antioch, California Fisherman’s Wharf, San Francisco

. 22-Inch Diameter FILL Tubex Pile . 45 Feet Deep Dense SM

. End-Bearing Into

Dense Sand BAY MUD CH

V. Dense SM

Static vs. PLT, Fisherman’s Wharf Bay Street, Emeryville

.16” Pre-stressed piles

.13 PLT’s in 2 shifts

.3 static tension tests

.Estimated saving to project: $500,000 Osterberg Cell Testing

. Calibrated, embedded, sacrificial jack within the test pile

Qs . Concept: Load base of the pile against the side shear, & eliminate reaction system

O-cell

Qp Osterberg Load Testing Typical O-CellLoad-Movement Curves

4 Extrapolated 3 Curve Measured Side Maximum 2 Shear Curve Load from O-Cell Test 1

0

-1 Pile wt. Measured End-

Movement (inches) Movement -2 Bearing Curve -3 -4 0 100 200 300 400 500 600 700 800 Load (kips) MRT-NEL C701, Singapore

Courtesy Jack Hayes

Multi-cell assembly -- attaching O-cells to bottom plate COMPARISON TEST, MRT-NEL C701, Singapore, March 1998. Comparison test Curves Kentledge Test versus O-cell equivalent top load-settlement curve 0

-10 -20 -30 O-cellO-cell Test Test Kentledge Test -40 Kentledge Test

-50

-60

-70

Settlement (mm) Settlement -80

-90

-100

-110

-120 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 Top Load (MN) O-Cell Test Advantages

. Elimination of Load Frame . Separation of End-Bearing and Side Shear . High Load Capacity (World Record 36,000 Tons! – St. Louis) . Improved Safety O-Cell Disadvantages

. Must arrange for simultaneous end-bearing and side shear failure or extrapolate. . Upward shear may be somewhat lower. . Expensive for lower capacity piles. Interpretation of Load-Settlement

. Variation in Capacity Interpretations . Davisson Failure Criteria Most Common Load, Q D/120 + 0.15 in

L/AE

QL/AE

Settlement Interpretation of Load-Settlement

. Double Tangent Failure Criteria

Q

u Load, Q

Settlement Interpretation of Load-Settlement

. Problems with Double Tangent

Q Q

u B u A Load, Q

B Settlement A Pile Instrumentation Strain Gauges Instrumentation

. Sister-bar (embedment) or weldable strain gauges  Resistance type gauges  Vibrating wire type gauges . Tell-tale rods . Extensometers Interpretation of Instrumentation

. Load = ε(AE)  What is area?  What is concrete modulus?  What is precision of strain measurement?  Residual Stresses? Load vs Depth

Load, Q

L Depth

Q3 Q2 Load Transfer (t-z Curves)

. Load Transfer, levels 2-3, = Q2 – Q3

. Unit Load Transfer, t = (Q2 – Q3)/(πDL)

. Displacement, z = (Displ at top) – Σ(ε*ΔL) t

z Residual Stress in Driven Piles Q Q Q

Residual Calculated True Load From Instruments Distribution Load vs Depth

Load, Q

Depth

Q4a Q4b Load Transfer (q-z Curves)

. End Bearing Pressure, 2 q = Q4 /(πr )

. Toe Displacement, z = (Disp. at top) – Σ(ε*ΔL)

q

z 3.5

t-z Curves 21 ft 3 46 ft 61 ft 2.5

2

1.5

1 Unit Side Friction (ksf)

0.5

0 0 0.1 0.2 0.3 0.4 0.5 0.6 Mid-Point Displacement (in)

350

Pile 5 q-z Curves 300 Pile 3

250

200

150

100

End-Bearing Pressure, Q (ksf) 50

0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Pile Tip Displacement, Z (in) Load-Settlement from q-z & t-z curves

z1= Load, Q, in Pile z +(Q +Q )L Layer 1 Layer 1 2 p 2 1 Q = 2 AE 1 t1 ΔQ s1= As1t1 t1 Q2+ ΔQs1

zmid-layer= Side shear, t shear, Side z2+(Qp+Q1)L1 Mid-layer disp., z Q =

z2= 4 AE Iterate for compatible load-displacement 2

Layer 2 zp+(Qp+Q2)L2 Q +ΔQ Layer 2 p s2 t2 L2 2 AE ΔQ = A t s2 s2 2 t2 Depth z = mid-layer Qp q z +(Q +Q )L t shear, Side p p 2 2 Mid-layer disp., z

4 AE Iterate for compatible load-displacement

Base

Qp = Apq q

End Bearing, q Bearing, End Toe Disp., z Assume initial toe displacement Load-Settlement Curve

Pile Head Load, Q1 That process gives one point on the curve Assume larger tip displacement and repeat

process for additional points

1 Pile Head Settlement,HeadPilez Additional Uses for q-z and t-z curves

. Downdrag conditions where the soil around the pile may move down relative to the pile

 Liquefaction Liquefaction Induced Downdrag  Fill settlement . Lateral pile groups to account for rocking