advances in foundation testing equipment and the potential...

©Strainstall 2016

Advances in Foundation Testing equipment and the

potential for dynamic testing of cast in place foundations

using the SIMBAT method in Singapore

©Strainstall 2016

Session One

Current practices used for the assessment of

new foundations and existing foundations

• Low Strain Frequency response & Impedance Profiling

• Parallel Seismic

• Downhole Magnetometer

• Sonic Logging Tomography

• Thermal integrity profiling

• Rate of Corrosion

Huw Williams - Product Manager Foundation Testing

©Strainstall 2016

Session TWO

The SIMBAT method for assessment of pile

performance dynamically.

• SIMBAT testing methodology and practical

considerations

• Comparison with other dynamic and RLT methods

• Relevant case histories

• The potential for SIMBAT in Singapore

Iwan Jones – Technical Authority Foundation Testing

©Strainstall 2016

Who we are: James Fisher History

©Strainstall 2016

Who we are: JF subsidiaries

©Strainstall 2016

Who we are: JF Global Locations

©Strainstall 2016

Materials Testing

What we do: Expertise

Structural Investigation

Test Equipment Pavement Analysis

SMART Asset

Management

Proof Testing

©Strainstall 2016

What we do: Expertise

Foundation Testing

Bi-Directional LT

Rate of Corrosion

Static Load testing

Low Strain testing Sonic Logging

SIMBAT Dynamic testing

©Strainstall 2016

Auger stays

behind casing

Casing is taken

past weak soil

layers

What Causes Defects?

©Strainstall 2016

Concrete slumps

into void leaving

Short casing… Bore partially

collapses

Casing is

extracted

and….

or Auger advances

deeper than casing

©Strainstall 2016

Pile cased through

running water

Pile washed out when

casing extracted

©Strainstall 2016

Pile is cased though

weak ground

Drilled through

bentonite or water

Tremie is placed

Pile is concreted

If tremie lifts out of

concrete…

A band of contaminated

concrete can be left

©Strainstall 2016

Pile Cracked in top few

metres in weak soil The good news is… its

easy to detect with PIT

©Strainstall 2016

Session One: Low Strain Frequency Response

©Strainstall 2016

TDR2 Pile Integrity Tester

©Strainstall 2016

Session One: Low Strain Time Domain

TECOLITE Pile Integrity Tester

©Strainstall 2016

Time Domain Test

Pile Head Velocity v Time Force Applied v Time

©Strainstall 2016

Fourier Transform

Convert to Freq Velocity / Force

Velocity

Mobility

©Strainstall 2016

Time domain

L = c t / 2

Frequency

Frequency domain

∆F ½∆F

L = c / 2 ∆F

Fixed End

Time t

L = c t / 2

Time domain

Frequency

∆F ∆F

L = c / 2 ∆F

Frequency domain

Free End

©Strainstall 2016

Length = c/2∆f

Stiffness = 2π f(m)

V/F(m)

Mobility = 1/ρcA

Frequency

Frequency Response (Mobility) Curve

©Strainstall 2016

Mobility = 1/ρcA

Frequency

F c = 3500m/sec

ρ = 2300Kg/m3

c = 4000m/sec

ρ = 2400Kg/m3

©Strainstall 2016

Frequency

Reduced section or concrete quality

Mobility = 1/ρcA

©Strainstall 2016

Mobility = 1/ρcA

Frequency

Increased section or concrete quality

©Strainstall 2016

Frequency Hz

1/ρcA

Short Pile – Weak Soil

©Strainstall 2016

Frequency Hz

1/ρcA

Long Pile - Stiff Soil

©Strainstall 2016

influenced heavily by pile head

diameter and upper soils

Stiffness is best used

comparatively for each site

Pile Diameter (m)

0.5 1.0 1.5

As guide should be approx

2 x diameter (m)

Dynamic Pile Head Stiffness – MN/mm

©Strainstall 2016

Simulation and Impedance Profiling

©Strainstall 2016

Software

Demonstration

©Strainstall 2016

Case History

• Frequency Response Testing

• Tower leg Foundations

• New Zealand

• Line Refurb

• Additional Load

• Wind Loading

©Strainstall 2016

Case History

High winds caused extensive

Power Infrastructure damage

©Strainstall 2016

Case History

Foundations were torn out

of the ground

©Strainstall 2016

Case History

Foundations were not as

Expected to be !!

©Strainstall 2016

Case History

All Pre-1960 tower foundations

were tested using frequency

response method

©Strainstall 2016

Case History : Accuracy of Depth Measurement

Length measurements were

generally within 5% accuracy

Assumed wave-speed velocity on

older piles found to be approx

3500m/sec

©Strainstall 2016

Case History : Impedance Profile

Impedance profiling used to check

presence of under-reaming – or not

- on all foundations

©Strainstall 2016

Case History : Now specified and used worldwide by power companies

Costa Rica Saudi Arabia Hungary

New Zealand United Kingdom Russia

©Strainstall 2016

Limitations

• Pile head needs to be accessible and in

good condition

• Limited info on pile toe

• Depth Limitation approx 25 diameters

• Not possible if connected to other

structures

• No information on performance under

• Unlikely to detect defects less than 10%

section

©Strainstall 2016

Session One: Parallel Seismic

©Strainstall 2016

PARAS Pile Integrity Tester

©Strainstall 2016

Applications

Determine depth of

existing connected

foundations

©Strainstall 2016

Applications

Can be used where low

strain PIT will not work,

i.e. sheets piling

©Strainstall 2016

How does it work?

• Install tube within 500m of pile

and beyond expected depth

• Grouted tube in place

• Fill with water

• Lower sensor on 0.5m

increments

• Impact structure with

instrumented hammer

• Measure transit time of signal

©Strainstall 2016

Data Analysis

Individual signals are processed

and correct first arrival time

determined

©Strainstall 2016

Depth and Soil Information

Pile depth and both soil and

concrete velocities can be

determined

Slope 1 = 3500 m/sec

Slope 2 = 500 m/sec

Pile Toe at 12.5m

©Strainstall 2016

Case History

• Old BBC HQ, London

• Pile Depth Determination

• Bored Cast Piles

©Strainstall 2016

Case History

©Strainstall 2016

Case History

©Strainstall 2016

Limitations

• Cost of tube installation can out weight cost of test

• Will only confirm continuity

• Will not detect local reductions or increases in pile section

• No information on performance

©Strainstall 2016

Session One: Downhole Magnetometer

©Strainstall 2016

Applications

• Depth of sheets steel piles

• Depth of Steel reinforcement in foundations

• Depth of steel casings

• Location of UXO

©Strainstall 2016

Methodology

• Detects changes magnetic fields perpendicular to borehole

• Ferrous material adjacent to borehole induces change in field

• Readings taken at 0.5m intervals

©Strainstall 2016

Case History

• Old BBC HQ

• Pile Depth Determination

• Bored Cast Piles

©Strainstall 2016

Fluxgate Magnetometer

Data Parallel Seismic Data

Case History

©Strainstall 2016

• Cost of tube installation can out weight cost of test

• Will not measure concrete continuity – only relative magnitude of steel present

• Will not detect local reductions or increases in pile section

• No information on performance

Limitations

©Strainstall 2016

Session One: Cross Hole Sonic Logging

©Strainstall 2016

SCXT3000 CSL System

©Strainstall 2016

How does it work?

The CHSL test is an ultrasonic test. It measures the time, t for an ultrasonic signal to travel

through concrete

Emitter Receiver t

©Strainstall 2016

The ultrasonic pulse is generated by a piezo-ceramic disc, when a high voltage (800V) is

applied across it.

The disc is exited horizontally at approx 50KHz, resulting in a horizontal displacement

How does it work?

©Strainstall 2016

Ceramics are encased

in plastic casings 25mm

in diameter

How does it work?

SCXT Probes

©Strainstall 2016

Emitter Receivers

The time, t will depend on the propagation velocity of the signal, c through the concrete and

the path length L

How does it work?

©Strainstall 2016

The propagation velocity, c is related to the properties of the concrete by:

How does it work?

c = √ E ρ

Therefore if the tube spacing is constant, then transit time t is a function of the properties of

the modulus and density concrete the signal is passing through

©Strainstall 2016

Transmitter Receiver

©Strainstall 2016

LED Display:

Profile No

Amplidude

Over speed

Warning

Buttons to Select

profiles and

control acquisition

Trigger pins

Acquisition light

SCXT3000 Winch unit

©Strainstall 2016

First Arrival Time traces

1 - 2 2 - 3 3 - 4 4 - 1 1 - 3 2 - 4

2D Tomography Software

©Strainstall 2016

Green areas correspond to normal FAT Values

©Strainstall 2016

Red areas correspond to comparatively low FAT Values – i.e. anomalies

©Strainstall 2016

h 1 - 2

time T0 T3

FAT to area colour conversion for trace 1 – 2.

©Strainstall 2016

Assessment Criteria Recommendations

• Analysis of First Arrival Time (FAT) is of primary importance

• Increases of FAT in excess of 20% are significant

• Increases of FAT less than 10% are not significant on their own

• The effect on overall pile integrity will depend on the number of profiles affected

• Analysis of signal energy is of secondary importance – tube debonding is not a defect but

can lead to significant reduction

• It is essential to view the whole signal and waterfall plot – not just the FAT & Energy plot

©Strainstall 2016

Software

Demonstration

©Strainstall 2016

Session One: Thermal Integrity Profiling

©Strainstall 2016

Session One: Thermal Integrity Profiling

©Strainstall 2016

TIP Limitations

• The test ceases to provide information once the concrete starts to cool.

• There is a limited functional window of a few days, reducing with plie diameter

• shaft diameter decreases.

• Improvement in delayed strength gain due to admixtures may not be detected within

limited window.

• Poor thermal conductivity of concrete could mean problems core of shaft are not detected

by peripheral sensors

• Accurate tomographic images of the location, shape and extent of an inclusion cannot be

produced in same manner as CSL

• Unlikely to be able to detecting or delineating an inclusion at the pile toe

• Cannot correlate temperature to concrete strength as with CSL

• Cost of disposable in place TIP sensors can be high

Session One: Thermal Integrity Profiling - TIP

©Strainstall 2016

Session One: Rate of Corrosion

©Strainstall 2016

BGCMAP Rate of Corrosion meter

©Strainstall 2016

Applications

• Rate of Corrosion of steel below

ground

• Foundations

• Lamp Posts and Columns

• Transmission towers leg

foundations

©Strainstall 2016

Cathode

O2 OH-

Corrosion Zone

LPR Theory

• Corrosion occurs at the anode,

where metal ions are oxidised

©Strainstall 2016

BGCMap

Half Cell Electrode

LPR Theory

• Current between electrode in

ground and steel is applied in

increments

• Changes in electric potential is

recorded

©Strainstall 2016

• Applied current and measured

voltage are plotted and is linear

about Free Corrosion Potential

• The slope is the Polarisation

Resistance Rp – from which

analysis is done

LPR Theory

©Strainstall 2016

Rp (ohm) Degree of Corrosion

19 Ohm and

Greater No Significant Corrosion Activity

9 – 18 Ohm Minor Corrosion Activity

6 - 8 Ohm On-Going Corrosion Activity

0 - 5 Ohm Significant Corrosion Activity

©Strainstall 2016

Icorr (mA) Degree of Corrosion

0.01 – 0.99 mA No significant corrosion

1.00 – 1.99 mA Minor Corrosion

2.00 – 2.99 mA On-Going Corrosion – Inspect

within 3 months

Greater than 3 mA Significant Corrosion – inspect

Immediately

©Strainstall 2016

Case History

• Transmission Tower Foundation

• New Zealand

• Assessment of Corrosion

potential below ground

• 64No Towers assessed

©Strainstall 2016

Line Tower Ave

Icorr(mA

Assessment

63 4.26 D 5.78 Severe

Corrosion

65 1.75 D 2.89 Ongoing

Corrosion

64 1.66 A 2.48 Ongoing

Corrosion

BEN-HAY

1519 1.54 B 1.93 Minor

Corrosion

224 1.38 A 1.58 Minor

Corrosion

225 0.98 A 1.45 Minor

Corrosion

BEN-HAY

1513 0.91 C 1.34 Minor

Corrosion

223 0.83 B 1.24 Minor

Corrosion

BEN-HAY

1524 0.68 A 1.07 Minor

Corrosion

Case History

BOB-OTA C 63 leg D

©Strainstall 2016

LPR – Limitations

• Measurement only indicates corrosion activity at time of test

• Cannot measure corrosion that has occurred

• Can be affected by seasonal ground conditions

• Best used comparatively to identify foundations at higher risk of corrosion

©Strainstall 2016

Session TWO

The SIMBAT method for assessment of pile

performance dynamically

©Strainstall 2016

Session Two: SIMBAT Dynamic Pile Testing

SIMBAT Dynamic Pile test system

©Strainstall 2016

Extremes of SIMBAT testing

75Kg Drop Weight 30,000Kg Drop Weight 1,000Kg Drop Weight

©Strainstall 2016

• Instrument pile, impact it and gather data

• Process data to get dynamic reaction

• Convert dynamic load to static and

produce load/settlement plot

• Create model from simulation and match

displacement

• Produce static load/settlement plot form

simulation data

How Does it Work ?

©Strainstall 2016

• Dynamic Performance of Piles under load

• Estimated static performance of Piles

• Permanent and elastic displacement

• Distribution of shaft resistance with depth

What Can it Measure ?

©Strainstall 2016

Pile Sensors

• Accelerometers and Strain Gauges

©Strainstall 2016

High Speed Theodolite

Simbat Theodolite – accurate to 0.14mm

at 5m @ 10,000Hz

SIMBAT High speed theodolite

©Strainstall 2016

Optical/Digital Theodolite

Accelerometers

Strain Gauges

SIMBAT Methodology

SIMBAT – Lyon, France

Total Force

Velocity from downward

Velocity from upward

wave (compressive

Y Combined Velocity

Downwards Force F

This lies midway between the total

force Ft and ZV

F = ½ (Ft + ZVt)

This is the F in a free pile.

It is shifted in time by 2l/c

and inverted.

The difference between the

upwards force measured

and the upwards force in a

free pile is the dynamic

reaction, Rdy

Simbat Software

Demonstration

Table of Results

Application of Damping Factor

Simulation

• Pile head displacement as

measured by the test (Blue)

and simulated value (Red)

• Simulated Displacement is

generated from a Finite

Element model where the

pile is split into 20 horizontal

layers. For each layer the

model calculates Quake,

Viscosity and Rupture

values

Static Load Simulation

SIMBAT Simulation

The purpose of the Simulation is twofold

• To Verify the predicted static load/settlement results obtained from the whole set of data

• To separate the soil resistances into those acting on the shaft and those acting on the toe

SIMBAT System Differences

Independent measurement of temporary & permanent displacement using high

speed Theodolite

Correction of velocity integration errors using displacement data

High and low strain blows to correct dynamic data without assuming J factors.

Simulation is modelled on displacement which is more accurate than velocity

Belgium Limelette Trial

Strainstall Group have attended numerous trials over the years, including one which was

organised by Professor Holeyman on behalf of the Belgian Building Research Institute.

This was an independent, blind trial and the SIMBAT system was assessed against the

standard dynamic pile testing systems manufactured by PDI and Profound system and also

against the Statnamic rapid load test system.

All dynamic tests were compared against static load tests carried out in the same field

Case History: Belgium Limelette Trial

4 Tonne Drop Weight

system

Instrumenting pile

4 Tonne Drop Weight

system

00 500 1000 1500 2000 2500 3000 3500

Load KN

B6 Atlas

A9 Olivier

A6 Omega

C10 Atlas

A7 Olivier

B8 Prefab

A10 Fundex

B10 Omega

B9 Prefab

B7 De Waal

C9 De Waal

A8 Fundex

Predictions

OLIVIER PILES

0 1000 2000 3000 4000

Load KN

A9 Simbat

A7 Simbat

A2 Static

C2 Static

C8 Statnamic

Notes: Static

load test reload

cycles omitted

for clarity. Pile

C2 ruptured at

2690KN

Predictions

OMEGA PILES

0 1000 2000 3000 4000

Load KN

A6 Simbat

B10 Simbat

A3 Static

C3 Static

C7 Statnamic

Predictions

PREFAB PILES

0 1000 2000 3000 4000

Load KN

B8 Simbat

B9 Simbat

B1 Static

B2 Static

C6 Statnamic

Predictions

FUNDEX PILES

0 1000 2000 3000 4000

Load KN

A8 Simbat

A10 Simbat

A1 Static

C1 Static

A5 Statnamic

Predictions

DE WAAL PILES

0 1000 2000 3000 4000

Load KN

B7 Simbat

C9 Simbat

A4 Static

C4 Static

C5 Statnamic

Predictions

Case History: Belgium Limelette Trial Conclusions

• Simbat accurate to within 11% of Static load

• Statnamic accurate to within 12% of static load

• Other Dynamic tests varied by up to 40% !

• Trail concluded that “based on dynamic

measurements SIMBAT predictions can be

considered as the fittest for all piles”

SIMBAT Sites

Key Advantages of SIMBAT System

• SIMBAT Accuracy can be comparable with Rapid Load testing

• SIMBAT testing rate is considerably higher than Rapid LT and

comparable with dynamic

• SIMBAT testing is cost effective compared to static testing

• SIMBAT test size is not limited by specialist drop weight system

• SIMBAT permanent and elastic displacement is recorded remotely

and accurately

• SIMBAT testing is less likely to damage working piles due to the

large cushion used

• SIMBAT testing can be carried out without assuming soil damping

factors

• Minimal disruption to site activity

Acceptance & Standards

• SIMBAT is widely used on projects in the UK

• Over 1500 Simbat tests carried out last year by Strainstall group

• Widely Accepted by consultants, contractors & building control

• Conforms to the ASTM standards for dynamic testing (D4945-12)

with minor differences but with additional features

• SIMBAT is included in ICE Manual of Geotechnical Engineering

• The SIMBAT methodology is in the process of being written into a

new EN ISO 22477 standard covering dynamic pile testing as a

specific annex.

SIMBAT Limitations

• Not designed for pile driving analysis.

• Not often used in marine environment due to requirement of stable

platform for theodolite.

• Cannot take into account long term effects such as creep, but then

neither can other dynamic or rapid load testing

Applied Load Duration Time Comparison

• Low strain pile integrity test 1ms

• Dynamic pile test PDA 5ms

• Simbat dynamic pile test 10ms

• Rapid dynamic pile test 60ms

• Statnamic dynamic load test 120ms

• CRP pile test 1hr

• Static Load pile test 19hr

• Building life 50 years

Pile Testing Methods Applied Load Duration Time

Log Scale

Huw Williams - Product Manager Foundation Testing

Strainstall

No. 1 Bukit Batok Crescent

#04-33 WCEGA Plaza Singapore

658064

Tel: +65 6561 4628

Questions Please!

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