Drilled Shaft Extraction

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Drilled Shaft Extraction

• Sign Shaft 8 Right
• I-4 Widening Volusia County
• FPN 408463-1-52-01

Kathy Gray, P.E. Florida Department of
Transportation (D-5) Mohamad Hussein, P.E. GRL
Engineers, Inc. Christopher Lewis, P.E. FG
Engineering, LLC
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Agenda

• Introduction/Background Kathy Gray
• Cross Hole Sonic Logging (CSL) Mohamad Hussein
  (GRL)
• Pile Integrity Test (PIT) Chris Lewis (FGE)
• Shaft Extraction Kathy Gray

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Site Location
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Drilled Shaft Log
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Cross Hole Sonic Logging (CSL) Mohamad Hussein,
P.E. GRL Engineers, Inc.
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Pull Probes From Bottom To Top
Place probes in bottom of tubes.
Stress Waves, emitted in one tube are received in
another one if concrete quality is satisfactory
Receive
Transmit
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Traditional analysis
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How to find defects?
Good
Defect

• Delayed First Arrival Time (FAT)
• Reduced signal strength (lower energy)

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Access Tube Measurements
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Cross-hole Analyzer - CHA
installing
pulling
operation
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Shaft with full section defect
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Can locate approximate location and extent of
each defect
Manual Tomography Simple and Fast Procedure
Select affected signals Manually draw it
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How much data is needed for Tomography?
If few tubes, then have large path sections
undefined, so should also have interior offset
scans.
If enough tubes, then finding interior defect can
be found easily with interior parallel scans only.
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2D horiz. Slice of a defect
3D body view
2D vert. slice
3D Tomography
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Pile Integrity Testing (PIT) Christopher Lewis,
P.E. FG Engineering, LLC
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Low Strain Integrity Testing

• Common Terms
• PIT (Pile Integrity Test)
• SIT (Sonic Integrity Test)
• Impulse Response
• Sonic Echo
• PET (Pile Echo Tester)

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Basic Concepts

• Multiple analysis techniques
• Time domain
• Frequency domain
• Two Velocity
• Profile Analysis (Signal Matching)

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Time Domain

• Most Common
• Data presented as a function of time
• Pile Dynamics equipment presents data as a
  function of length
• Uses assumed values of wave speed and/or
  foundation length
• This allows fast, reliable evaluation of data in
  the field

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Stress Wave Propagation

• Impact made at pile top
• Reflections represent changes in impedance
• Wave speed ? Material Density
• Stress waves travel faster in denser material
• Length ? Wave speed ? Observed Reflections

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Impedance Changes

• Foundation material property changes
• Geometric property changes (cross-sectional area)
• Soil resistance
• Cracks
• Changes in soil strata

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Testing Considerations

• Test Limitations
• Length/Diameter Ratio (typically length no more
  than 30 diameters)
• Other conditions
• Soil Profile
• Construction Procedure
• Construction Records
• Serviceability
• Responsibility !

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Pile Dynamics Equipment
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FGE Test Procedure

• Prepare Shaft/Pile top
• Level and clean area where accelerometer attaches
  and impacts will be made.
• 3 to 4 spots around the perimeter and 1 spot just
  off center
• Set up PIT collector
• Attach accelerometer
• Impact Shaft/Pile top with standard 2 pound
  hammer
• Review and save data
• Acquire second set of data with another hammer
• Move to next location
• Check memory to ensure data is saved

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Data Analysis

• Data collected is downloaded to PC for further
  analyses using PIT-W software.
• This software is used for data management,
  manipulation and presentation

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Data Management

• Records can be
• Deleted
• Averaged
• Selected for presentation in report
• Appended to include comments
• Arranged/Sorted

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Data Manipulation

• Change wave speed and length
• Magnify and filter collected data
• Importance of Experience
• False toe
• Over magnification of other shaft features
• Filter out defects

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Data Presentation
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Basic Evaluation of Data

• Decreased Impedance
• Reflection above neutral or zero axis of graph
  prior to toe reflection
• Usually indicates potential necking or void
• Increased Impedance
• Reflection below zero axis of graph prior to toe
  reflection
• Usually a result of larger cross-section

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Subject Shaft
Reported Areas of Decreased Impedance
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Shaft Extraction Kathy Gray, P.E. Florida
Department of Transportation District 5
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Upper Anomalies
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Lower Anomaly
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Conclusions

• Cross Hole Sonic Logging Found Defects
• Pile Integrity Testing Found Defects
• Both Methods Have Limitations
• 2 Methods together may be best approach

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Questions ?
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