Thermal Integrity Profiling

Transcription

1 Thermal Integrity Profiling Quality Assurance Test Method to Detect Drilled Shaft Defects Gray Mullins, Ph.D., P.E. Professor, University of South Florida AFS30 Committee Meeting, TRB 2011

2 Overview Thermal Integrity Profiling uses the measured internal shaft temperature generated by hydrating concrete to assess the presence or absence of intact concrete. The energy produced in one 9 yd truck of concrete is equivalent to 450 lbs of TNT.

3 Thermal Integrity Profiling Drilled Shaft Reinforcement Cage Logging Tubes Normal Heat Signature

4 Thermal Integrity Profiling Drilled Shaft Anomaly Reinforcement Cage Logging Tubes Interrupted Heat Signature

5 Field Testing Depth Encoder Assembly Data Acquisition System Access Tubes

6 Data Collector Equipment Thermal Probe Infrared Sensors Depth Encoder Assembly Data Acquisition System

7 Analysis Internal temperature measurements are sensitive to necking, bulging, inclusions, and cage alignment. The available time of testing is dictated by the shaft diameter and mix design. The timeframe for testing (in days) equals the diameter (in feet). High slag content mixes extend testing time.

8 Single Shaft Heat Signature Elevated Shaft Concrete Temperature Distribution Elevated Soil Temperature as well S46 S37 S28 S19 S10 S1

9 Level 1 Levels of Analysis Direct Observation of Temperature Profiles Level 2 Superimposed Construction Logs / Concrete Yield Level 3 3-D Thermal Modeling Level 4 Signal Matching Additional / Optional Inclination Measurements

10 Level 1: Direct Observation (Field) Identify top and bottom of shaft Verify shaft length Confirm cage alignment Locate changes in shaft diameter Locate immediate areas of concern

11 Depth (ft) Scatter Creek Shaft A Temperature (deg F) T1 T2 T3 T4 Avg Field Observations Little to no cage eccentricity (all tubes same temp throughout) Water table at (causes sloughing until slurry is fully in place) Bottom of casing at Clean top and toe signature (approximate 1 diameter temperature roll-off top and bottom) Good Shaft 40

12 Cage Alignment (Level 1) All tubes have same temperature when cage is concentric. A normal cylindrical shaft with an offset cage is shown as equally higher and lower temperatures on opposite sides of cage. Average of all tubes represents the centered cage temperature

13 Temperature (F) Temperature (C) Temperature Distribution (10 ft diameter shaft) Position (m) Normal Centered Cage Temp Cage Diameter at Tubes Excavation Diameter Position (ft)

14 Temperature (F) Temperature (C) Effect of Cage Misalignment Position (m) Tube Highest Measured Temp Lowest Measured Temp Tube Cage Diameter at Tubes Excavation Diameter Position (ft)

15 Depth (ft) Depth (m) Pier 6 Shaft B Temperature (F) Cage Alignment Tube 1 61C (142F) Avg (bold) 66C (150F) Tube 6 71C (160F) Temperature (C) T9 T8 175F 79C 150F 66C 125F 52C T1 T2 T3 T4T10 T5 T6 T7 T8 T9 T10 Avg T7 T6 N T1 T5 T2 T4 T3

16 Level 2: Added Field Records Confirm direct observations Establish relationship between concrete volume placed and measured temperature Predict as-built shaft radius, shape, and cover Correlate soil strata to thermal conductivity and observe influence on less prominent temperature fluctuations

17 Depth (ft) Florida Turnpike Lake Worth Temperature (deg F) T1_2 T2_2 T3_2 T4_3 T5_1 T6_1 T7_1 Average Level 1 Observations Cage misaligned (tube temps vary across shaft) Avg. shows shape Probable rock socket 75ft (step in shaft temp; less eccentricity) Clean top and toe signature Upper step / temporary casing at 14 ft Need Level 2 Information

18 Depth (ft) Florida Turnpike Lake Worth Exit Method Shaft Temperature (deg F) T1_2 T2_2 T3_2 T4_3 T5_1 T6_1 T7_1 Average Grnd Surf TOS WT BOC TOLime TOR BOS Confirm Observations Add const. log info Top of shaft Grnd surface Water table Bot of casing Top of limestone Top of good rock Bot of shaft Add concrete yield information 100

19 Concrete Yield Plots Depth change per truck Volume per truck Convert to avg diam or radius per truck

20 Depth (ft) Method Shaft Temperature (deg F) No Correction for Over-pour Concrete Average Grnd Surf TOS WT BOC TOLime TOR BOS Effective Diam. Theoretical Diam. Concrete Yield to Diam Plot Plot theoretical diam or radius Top and bottom truck weakest information Shaft Diam (ft) No Correction for Tremie filling / volume

21 Depth (ft) Method Shaft Temperature (deg F) No Correction for Over-pour Concrete Average Grnd Surf TOS WT BOC Temp / Diam Correlation Shape of avg. profile mimics diameter from concrete yield Shaft Diam (ft) TOLime TOR BOS Effective Diam. Theoretical Diam. No Correction for Tremie filling / volume Average temp. is determined for a given truck yield (diam.) Results plotted to establish correlation

22 Radius (in) Temperature to Radius Conversion R = T Temperature (F)

23 Depth (ft) Radius (in) t1 t2 Individual Tube Positions t3 t4 t5 t6 t7 avg Good agreement with yield plot information TOS WT BOC TOLime TOR Check tube / cage cover 80 BOS Effective Radius

24 Depth (ft) 0 Effective Radius (in) Outer Radius of Cage t1 t2 t3 t4 t5 t6 t7 avg TOS WT BOC TOLime TOR BOS Effective Radius Individual Tube Positions Check tube / cage cover Three tubes touch side walls others with reduced cover 100 Design Radius of Shaft

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26 Depth (ft) Depth (m) Temperature (F) Tube 1 Tube 3 Tube 5 Avg Temperature (C) Steel Logging Tubes Known Anomaly PVC Logging 5 3 Cross-Section A Top Anomaly Cross-Section B Bottom Anomaly

27 Summary Thermal profiling of shafts shows presence or absence of intact concrete both inside and outside reinforcement as well as confirmation of proper cover and cage alignment. Strong correlations between measured temperature and radius provide an as-built shape of the shaft. Testing is performed shortly after concreting expediting acceptance or rejection.

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29 Sensitivity Large anomalies are detected farther away Smaller anomalies must be closer to tubes Miniscule anomalies may not be detected but are of no importance. Next three slides show a common tremieinduced anomaly in a 4ft diameter shaft.

30 Depth (ft) Temperature (deg F) ft Diameter Shaft 3 ft Diameter Cage 4 DT = 1.38 o F 10 in Diameter Anomaly 6 11 inch Separation 8 10 Anomaly in center of cage 12 14

31 Depth (ft) Temperature (deg F) ft Diameter Shaft 3 ft Diameter Cage 4 DT = 1.76 o F 10 in Diameter Anomaly 6 6 inch Separation 8 10 Anomaly just off center 12 14

32 Depth (ft) Temperature (deg F) ft Diameter Shaft 3 ft Diameter Cage 4 DT = 3.51 o F 10 in Diameter Anomaly 6 0 inch Separation 8 10 Anomaly adjacent tube 12 14

33 Level 3: 3-D Thermal Modeling Confirms Level 1 and Level 2 Establishes the anticipated shaft temperature for a given size of shaft and time of testing. Verifies top and bottom roll-off distribution. Can be used to establish the field testing window.

34 Level 3: 3-D Thermal Modeling Predicting Shaft Temperature Must know mix design with detailed cement and flyash reports (can change monthly) Must know geometry of shaft or other concrete element in question Must know environmental conditions (e.g. air temp, soil type, soil temp, etc.)

35 Hydration Energy (Schindler, 2005) Cement Energy Production Total Energy Production

36 Hydration Energy (Schindler, 2005) Degree of Hydration Rate of Energy Production

37 Input Parameters (from concrete supplier)

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39 Temperature (deg F) Thermal Testing Timeframe 4000-P Mix Design 160 4ft Diameter 6ft Diameter 8ft Diameter ft Diameter Optimal Testing Window Acceptable Testing Window Time (hrs)

40 Level 4: Signal Matching Advanced 3-D modeling Variable soil strata Tailors the modeled shape of the shaft to match the field measured temperatures Variable climatic inputs

41 St. Augustine Bridge of Lions

42 Bridge of Lions Pier 25 Shaft 3 3ft diameter

43 Elevation (ft) Depth (ft) 0 Temperature (deg F) Temperature (deg F) BOC Measured Results Model Results Tube 1 Tube 2 Tube

44 Elevation (ft) Elevation (ft) 0 Temperature (deg F) Tem perature (deg F) BOC Tube Tube 1 Tube Tube 2 Tube Tube 3 110