Nondestructive Evaluation of Drilled Shafts in Iowa by Thermal Integrity Profiling
Jeramy C. Ashlock Drilled Shaft Defects
FHWA-NHI-10-016 Drilled Shaft Manual (2010) 2 Drilled Shaft Defects
Mullins and Winters (2011), “Infrared Thermal Integrity Testing Quality Assurance Test Method to Detect Drilled Shaft Defects”, WSDOT Research Report WA-RD 770.1 3 4 FHWA-NHI-10-016 Drilled Shaft Manual (2010) NDE Methods for Drilled Shafts
• Crosshole Sonic Logging (CSL) – Only provides information inside rebar cage between CSL tubes Large portion of • Nuclear Gamma-Gamma the concrete Logging (GGL) remains untested – Can provide information outside rebar cage, but only within 3-4 inch diameter zone
• Thermal Integrity Profiling (TIP) – Influenced by concrete of entire shaft cross-section, as well as soil thermal properties
5 Crosshole Sonic Logging (CSL) ASTM D 6760-08
6 Limitations of CSL Test
1. Only detects flaws between CSL pipes, not in the critical zone outside the rebar cage 2. Does not indicate amount of rebar cover 3. Results are adversely affected by debonding of access tubes 4. Tests cannot be performed sooner than 3 to 7 days after casting depending on shaft size (ASTM D 6760)
7 IDOT CSL Specifications
IOWA DOT - OFFICE OF BRIDGES AND STRUCTURES - LRFD BRIDGE DESIGN MANUAL - 6.3: 1: Due to lack of redundancy in many applications, quality control of drilled shafts is important. The office considers it necessary to test each drilled shaft used for support of bridges, light towers, and sign structures. The office requires crosshole sonic log (CSL) testing, with at least four 2-inch (50-mm) diameter pipes equally spaced inside the reinforcing cage. The testing is covered in the Iowa DOT Standard Specifications [IDOT SS 2433], which are applicable for bridge foundations, and in a developmental specification [IDOT DS-09032] for support structure foundations.
All drilled shafts shall have provisions for crosshole sonic logging (CSL), and the designer shall show on the plans a CSL access pipe layout for each unique drilled shaft. One 2-inch (50-mm) diameter access pipe shall be provided per 1 foot (300 mm) of shaft diameter, but there shall be a minimum of four access pipes per shaft. The access pipes shall be equally spaced around the inside perimeter of the reinforcing cage. The layout should provide adequate space around CSL access pipes for concrete consolidation. The layout should avoid congested areas, especially between column and drilled shaft reinforcing cages and should avoid placing reinforcing bars in a direct line between any two access pipes.
8 IDOT CSL Specifications
Standard Specifications [IDOT SS 2433]: • Plastic access ducts not allowed • CSL test after minimum of 48 hours, maximum of 7 days • 2 inch diameter Schedule 40 pipe conforming to ASTM A 53, Grade A or B, Type E, F, or S. • “Install the access pipes in straight alignment and parallel to the vertical axis of the reinforcing cage. Access pipes shall have 2 inches (50 mm) concrete cover at the bottom of the shaft or extend to the top plate of a load cell placed at the bottom of the shaft. When a load cell is located above the bottom of the shaft, fit the access pipes with watertight slip joints between the load cell bearing plates.” • Submit the test results, analysis, and interpretation for the shafts to the Engineer within 7 calendar days of testing. The Engineer will: – Determine final acceptance of each shaft, based on the CSL test results and analysis for the tested shafts, and – Provide a response within 5 working days after receiving the test results and analysis submittal.
9 Gamma-Gamma Logging (Gamma Density Logging) • Probe containing Cesium-137 is lowered into access pipes • Backscattered radiation is measured using a photon counter • Gives nuclear measurements of concrete density around access pipes
10 FHWA-NHI-10-016 Drilled Shaft Manual (2010) Limitations of Gamma-Gamma Logging
• Concrete is only measured within 3”-4” cylindrical zone around access pipes, majority of shaft cross-section is not tested
• Regulations and certification for nuclear devices
11 Shaft Coverage by CSL and GGL
Mullins and Winters (2011), “Infrared Thermal Integrity Testing Quality Assurance Test Method to Detect Drilled Shaft Defects”, WSDOT Research Report WA-RD 770.1 12 TIP Testing Procedure
• Measure temperature vs. depth during concrete curing using; 1. Infra-red probe in access tubes (black steel CSL tubes or schedule 40 PVC) Or
2. Thermal wires; pre- fabricated strings of thermocouples sampled every 15 minutes
13 TAP for TIP vs. TAPP for TIP
• Thermal Acquisition Port (TAP) for Thermal Wires
• Thermal Acquisition Port for Probes (TAPP) for Thermal Probe
14 Optimum Testing Time
• Depends on shaft size, concrete mix, soil temperature profile, soil thermal properties… • Corresponds to time of maximum temperature gradient from center to edge of shaft • Is roughly 20-30 hours after concrete placement for 4 ft - 5 ft shafts • Can be calculated for given mix design, shaft size, soil properties 15 Optimum TIP Testing Time
Source: Mullins et al. (2009) 16 Infra-red Probe vs. Thermal Wires
Method Advantages Disadvantages Infra-red • Probe is re-usable, no need to • Testing is time-consuming: water probe purchase equipment in future must be pumped from/to CSL tubes, • Continuous monitoring of data not lower probe slowly while recording feasible temperature • Requires CSL tubes or PVC access tubes Thermal • Installation is quick • Thermal wires are sacrificial, must be wires • Temperature is automatically logged purchased for each shaft at continuously $5/ft (times 4-6 wires per shaft) • Depth-encoding wheel not needed • Resolution is 1 ft interval • CSL tubes not needed • Depths are pre-determined (1 ft intervals) • Much cheaper/easier to continuously record data 17 Heat Flow and Temperature Profile in Shaft
Johnson, K. (2014), “Temperature Prediction Modeling and Thermal Integrity Profiling of Drilled Shafts”, ASCE GeoCongress, 18 Atlanta, GA. Temperature at Given Radius Increases with Shaft Diameter
Johnson, K. (2014), “Temperature Prediction Modeling and Thermal Integrity Profiling of Drilled Shafts”, ASCE GeoCongress, 19 Atlanta, GA. Hyperbolic Tangent Correction to Account for Axial Heat Flow at Top/Bottom
Johnson, K. (2014), “Temperature Prediction Modeling and Thermal Integrity Profiling of Drilled Shafts”, ASCE GeoCongress, Atlanta, GA. 20 TIP Data Interpretation
• Increased temperature: more concrete (bulging), or tube closer to center (cage misalignment) • Decreased temperature: less concrete (necking), or tube further from center • Changes in alignment or cross-section size determined from opposite tubes Mullins and Winters (2011), “Infrared Thermal Integrity Testing Quality Assurance Test Method to Detect Drilled21 Shaft Defects”, WSDOT Research Report WA-RD 770.1 Data Analysis: Levels 1 through 4
Level 1: Comparison of temperature profiles (usually sufficient for routine projects) – Identifies top and bottom of shaft, overall shaft length, cage alignment (qualitatively), changes in shaft diameter and immediate areas of concern. Level 2: Superimpose the concreting logs and construction data (elevations of shaft, casing, water table) – Gives temperature-radius correlation to define shaft shape – Quantifies cage eccentricity cover distance Level 3: Three dimensional thermal modeling Level 4: Signal matching numerical models to field data “to discern location and size of inclusions that produce no heat” (Mullins et al. 2007) Source: Mullins and Winters (2011) 22 Analysis: Level 1
Some cage misalignment. Bulging near 32 ft Good alignment, little (sloughing at w.t.) and 60 ft. Necking near 55 ft. necking/bulging Access tube stickup above 15 ft.
23 Source: Mullins and Winters (2011) Analysis: Level 2
Makes use of theoretical temperature distribution in shaft & soil at a given depth Cage alignment at 40 ft depth
Source: Mullins and Winters (2011) 24 Analysis: Level 2
Temperature to radius correlation
Source: Mullins and Winters (2011) 25 Analysis: Levels 3 and 4
• Thermal modeling of hydration energy and heat dissipation by finite difference method • Requires concrete mix design parameters for Schindler’s (2005) heat production equation:
– % MgO, C2S, S3A, C3S, SO3, C4AF, Flyash, SO3, CaO, Slag – Blaine (m2/kg), Energy (kJ/kg) – , , (hrs.)
Source: Mullins and Winters (2011) 26 CSL Defect Definition
Jalinoos et al. (2005), “Defects in Drilled Shaft Foundations: Identification, Imaging, and Characterization”, FHWA report 27 CFL/TD-05-003. GGL/GDL Defect Definition
Jalinoos et al. (2005), “Defects in Drilled Shaft Foundations: Identification, Imaging, and Characterization”, FHWA report 28 CFL/TD-05-003. CSL Rating / Acceptance Criteria
FHWA-NHI-10-016 Drilled Shaft Manual (2010) 29 TIP Defect Definition / Acceptance Criteria?
and
Winters, D. (2014), “Comparative Study of Thermal Integrity Profiling with Other Non-Destructive Integrity Test Methods for 30 Drilled Shafts”, ASCE GeoCongress, Atlanta, GA. Motivation for This Study
• Mullins and Ashmawy (2005), Mullins et al. (2007), and Mullins and Winters (2011) successfully detected the presence of relatively large, deformable defects consisting of bags of soil cuttings tied to the rebar cages
• It would be useful to be able to determine defect size/location the thermal data – For acceptance/denial criteria – To know where to perform concrete coring – To determine shaft’s reduced structural moment and shear capacities
31 Detection of Defects
• Defects were detected in previous studies by Mullins et al. (total size was ~10% of shaft area) • Anomalies (no heat generation) created using sand bags of soil cuttings or wooden blocks • General location of defects was sucessfully indicated by Level 1, 2, 3, 4 analyses • Accuracy of TIP method in determining precise location/extent of defects not known • Anomalies were not created inside rebar cage
32 Mullins and Winters (2011), “Infrared Thermal Integrity Testing Quality Assurance Test Method to Detect Drilled Shaft Defects”, WSDOT Research Report WA-RD 770.1 33 Goals of Research Project
• Assess the accuracy and resolution of TIP in detecting the known location and extent of more rigid flaws having fixed geometries – Determine minimum detectable defect size – Develop new optimization/signal-matching techniques to determine location and size of defects both inside and outside the rebar cage • 5 test shafts on Iowa DOT bridge projects – Results of first 2 shafts in this presentation – Shafts also used for O-cell tests in LRFD study 34 Properties of Test Shafts
Property Test Shaft 1 Test Shaft 2 Defect type poor quality concrete aggregate/sand/water Total shaft length, m (ft) 25.9 (84.9) 23.5 (77.0) Length of upper cased zone, m (ft) 3.47 (11.4) 3.61 (11.8) Nominal shaft diameter, m (in.) 1.52 (60) 1.52 (60) Diameter in cased zone, m (in.) 1.83 (72) 1.83 (72) Diameter of defects, mm (in.) 152.4 (6) 152.4 (6) Height of defects, m (ft) 0.3 (1.0) 0.3 (1.0) Upper defect depth range, m (ft) 2.29-2.59 (7.58.5) 4.42-4.72 (14.515.5) Lower defect depth range, m (ft) 8.69-8.99 (28.529.5) 9.75-10.1 (3233) Upper defects-to-shaft area ratio 2.8% 8% Lower defects-to-shaft area ratio 4% 8% Shaft 7-day strength, MPa (psi) 37.4 (5,400) 33.3 (4,825) Defect 7-day strength, MPa (psi) 3.94 (572) Not applicable O-cell depth range, m (ft) 21.521.9 (70.571.8) 19.319.7 (63.364.7)
Cage radius, mm (in.) 610 (24) 616 (24.25) 35 Shaft 1 Upper Defects
Tube 5
Tube 5
Tube 1
Tube 1
36
Shaft 1 TIP Test US 69 over DSM River overflow Middle
37 Shaft 1 TIP Test US 69 over DSM River overflow Middle
38 Shaft 1 TIP Test US 69 over DSM River overflow Middle
39 Shaft 2 Upper & Lower Defects
Tube 5 Tube 1
Lower defects
Upper defects Tube 2
Tube 4 Tube 3 40
Shaft 2 TIP Test US 69 over DSM River overflow South
41 Upper defect
Lower defect
O-cell
(a) (b) FIG 3: Crosshole sonic logs for Tube pair 5-1 of Shaft 1 42 (a): energy and waterfall plot, (b): energy and picked first arrival time (a) (b) (c) FIG 4: Thermal integrity profiling temperatures and soil profile for Shaft 1 (a) temperature; (b) apparent, theoretical, concrete log, and cage radii; (c) soil profile 43
Upper defect
Lower defect
O-cell
(a) (b) FIG 5: Crosshole sonic logs for tube pair 2-3 of Shaft 2 44 (a): energy and waterfall plot, (b): energy and picked first arrival time (a) (b) (c) FIG 6: Thermal integrity profiling temperatures and soil profile for Shaft 2 (a) temperature; 45 (b) apparent, theoretical, concrete log, cage, and SoniCaliper radii; (c) soil profile Test Shaft 3
• 5 ft diameter • Defects outside cage at 2 elevations • Upper defects: glacial till compacted/formed in sand bags • Lower defects: poor-quality concrete (675/930/980 psi at 7/14/21 days) • Target area ratio of 10% with 16 in. defect height • TIP probe method used • Thermal strings also logged for 7 days
46 Test Shaft 3 US 35 and Cumming Interchange, Warren County
• PDI donated six 100’ thermal wires and TAP datalogger for Shaft 3 – Will see temperature of entire shaft evolve over time – Will compare temperature profiles from probe, wires – Probe has higher resolution (~3 in. vs. 12 in.) – Wires will indicate what the
optimum probe test time was 47 Thermal Wires
48 Test Shaft 3
49 Test Shaft 3
50 Test Shaft 3
51 52 53 54 55 56 Conclusions
• Both CSL and TIP methods clearly indicated the presence of the O-cell • Neither method strongly signaled the presence of the smaller defects • Larger defects were detected by CSL testing, and resulted in minor local temperature reductions in TIP tests • This study indicates a possible lower-bound resolution of at least 8% of the shaft cross-sectional area for a defect to be reliably detected by TIP • Further study is needed
57 Acknowledgements
• Iowa DOT • Mid-America Transportation Center • PDI: Garland Likins, Tim Rains • Mohammad Fotouhi (ISU) • Gray Mullins (USF) • GSI Engineering, Urbandale, IA • United Contractors • Jensen Construction Co. • Longfellow Drilling • Loadtest USA
This research was supported by the Mid-America Transportation Center and the Iowa Department of Transportation. The views and conclusions expressed herein are those of the authors and do not necessarily reflect the opinions of the sponsoring organizations. 58 Thank You
Questions?