Drilled Shafts Defects, Detection & Effects

Transcription

1 Drilled Shafts Defects, Detection & Effects SPONSORS FHWA ADSC

2 Background Growth in Drilled Shaft Usage NDT Seismic Considerations Equipment QA/QC Difficult Interpretation Capacity of Defected Shafts?

3 Objectives Defects What is the smallest detectable defect size? Which NDT methods are most reliable? Detection of multiple defects Effects of Defects Capacity Adequacy of Statnamic Load Testing in Varved Clay (Not Shown)

4 Integrity Testing Methods Down Hole Techniques Crosshole Sonic Logging (CSL) Single Hole Sonic Logging (SSL) Crosshole Tomography (CT) Surface Techniques Sonic Echo (Pulso echo, Acoustic Wave Reflections) Sonic Mobility (Impulse Response) Gama-Gama Not used

5 Project Layout Reaction Shafts Load Test Shafts Statnamic Shaft

6 ... Soil Profile NGES UMASS Site 12 feet over-consolidated crust OCR = 6 10 N = 5 15 Soft Grey Connecticut Valley varved clay PI = Su= psf (34 38 kpa) N = ft Misc. Clay / Silt Fill 8 ft Sandy Silt Ground Surface Elevation Grey Varved Clay

7 Construction 36 in. augured hole to approximately 20 feet 40-Inch OD temporary casing inserted into augured hole Remainder augured to 47 feet without casing or slurry Holes remained open for several hours Full length Reinforcement inserted into hole Concrete placed using free fall and tremie techniques 3 ft. section of casing used to form the shaft above grade

8 .. Shaft Dimensions Above Grade Diameter = 36 Inches Length = 1 3 ft Top Section Diameter = 40 inches Length 20 ft Bottom Section Diameter = 36 inches Length = 27 ft TOTAL EMBEDED LENGTH = 47 ft Ground Surface Elevation D= 40 in. L = 20 ft. D= 36 in. L = 27 ft.

9 Built in Defects Built in Defects Area= ft2 Length 1 4 ft Necking reduces diameter to 22 in. Attached to rebar cage Construction Defects Soft Bottom Locations Along the shaft length Multiple defects per shaft

10 NDT Access Tubes 2-inch black iron NDT pipes in all shafts. All shafts (except Shaft 3) had 4 access tubes. Shaft 3 had 3 access tubes.

11 Instrumentation Shaft 2 and 4 5 levels of strain gages 5 levels of telltales Inclinometer casing Shaft 1, 3, and levels of strain gages 2 levels of telltales Inclinometer casing Shaft 6 5 levels of strain gages Inclinometer casing 2-inch black iron NDT pipes in all shafts

12 Class-A Defect Prediction Olson Engineering Geosciences Testing and Research STS Consultants Construction Technologies Labratories (CTL) Prof. Finno, Northwestern University and Prof. Gassman, University of South Carolina GZA Geoenvironmental B&A GRL

13 Shaft 1 Shaft 1 As Built NDT Testers - Testing Technique Depth, m (ft) No. Legend 1 - ST 2 - DHT 3 - ST 4 - DHT 5 DHT 6- MULT 7- DHT 8- MULT Void 1.5 (5) Necking Soil 3.0 (10) A Change in diameter Low Density Concrete Shaft Oversize 4.6 (15) B 6.1 (20) Defect Minor defect 7.7 (25) 9.2 (30) C, D 10.7 (35) 12.2 (40) E 13.7 (45) F 15.2 (50)

14 Shaft 2 Shaft 2 As Built NDT Testers - Testing Technique Void Depth, m (ft) No. Legend 1 - ST 2 - DHT 3 - ST 4 - DHT 5 - DHT 6- MULT 7- DHT Necking Soil Change in diameter Low Density Concrete Shaft Oversize Defect Minor defect 1.5 (5) 3.0 (10) 4.6 (15) 6.1 (20) 7.7 (25) 9.2 (30) 10.7 (35) Soft Bottom Structurally Sound 12.2 (40) 13.7 (45) 15.2 (50)

15 Shaft 3 Shaft 3 As Built NDT Testers - Testing Technique Depth, m (ft) No. Legend 1 - ST 2 - DHT 3 - ST 4 - DHT 5 - DHT 6-MULT 7- DHT 8-MULT Void Necking Soil Change in diameter Low Density Concrete Shaft Oversize Defect 1.5 (5) 3.0 (10) 4.6 (15) 6.1 (20) A Minor defect 7.7 (25) B 9.2 (30) C 10.7 (35) 3 NDT Tubes 12.2 (40) 13.7 (45) 15.2 (50) D

16 Shaft 4 Shaft 4 As Built NDT Testers - Testing Technique Depth, m (ft) No. Legend 1 - ST 2 DHT 3 - ST 4 - DHT 5 - DHT 6-MULT 7-DHT 8-MULT Void Necking Soil Change in diameter Low Density Concrete Shaft Oversize Defect Minor defect 1.5 (5) 3.0 (10) 4.6 (15) 6.1 (20) 7.7 (25) A B Voids & soil inclusions 5 45% of cross section 9.2 (30) 10.7 (35) 12.2 (40) 13.7 (45) C D E 15.2 (50) F

17 Shaft 5 Void Necking Soil Change in diameter Low Density Concrete Shaft Oversize Defect Shaft 5 As Built NDT Testers - Testing Technique Depth, m (ft) 1.5 (5) 3.0 (10) 4.6 (15) 6.1 (20) No. Legend 1 - ST 2 - DHT 4 - DHT 5 - DHT 6-MULT 7-DHT 8-MULT Minor defect 7.7 (25) A 9.2 (30) 10.7 (35) B 12.2 (40) C 13.7 (45) D 15.2 (50)

18 Shaft 6 Shaft 6 As Built NDT Testers - Testing Technique Depth, m (f t) No. Legend 1 - ST 2 - DHT 4 - DHT 6-MULT 7-DHT Void Necking Soil Change in diameter Low Density Concrete Shaft Oversize Defect Minor defect 1.5 (5) 3.0 (10) 4.6 (15) 6.1 (20) 7.7 (25) 9.2 (30) 10.7 (35) 12.2 (40) 13.7 (45) 15.2 (50)

19 Conclusions, Down Hole Methods Defects larger than 10% of cross-section were EASILY detected. Defects smaller than 5% of cross-section were NOT detected. Unable to locate defects outside cage, including soft bottoms. Soil inclusions were more difficult to detect than voids. False positives were common.

20 Conclusions, Surface Methods Better than previous studies. Able to locate VOIDS down to 6% of cross section! Able to locate SOIL INCLUSIONS down to 17% of cross section. Up to 3 defects were located per shaft. Difficult to detect soft bottom.

21 Load Tests Static load tests 2 shafts 4 tests (shafts re-tested 8 hours later) Quick incremental test method Continuous rate of loading (not shown) Statnamic testing (not shown) 3 shafts 5 tests Capacity predictions H. Poulos won

22 Penetration, cm Load Test Shaft 2 Soft Bottom No Structural Defects Davidson s Capacity = 1000 kn (225 kips) 5% of diameter = 1200kN (270 kips) Mobilized Cu in end bearing = 34 kpa (710 psf) Unit skin friction = 17.4 kpa (360 psf) Davidsons's Failure Line Load m 8.5 m 5.5 m Load, kips Load, kn

23 Penetration, cm Penetration, in Load Test Shaft 4 Structural Defects Davidson s Capacity = 950 kn (213 kips) 5% of diameter = 1060 kn (238 kips) Davidsons's Failure Line Load, kips 0 1 Mobilized Cu in end bearing = 51 kpa (1065 psf) Load 1.9 m 4.74 m 10.9 m Load, kn

24 Penetration, cm Load Test Shaft 4-Reload 8 hours later Load, kips Davidson s Capacity = 880 kn (198 kips) % of diameter = 1000 kn (225 kips) Mobilized Cu in end bearing = 42.5 kpa (890 psf) Unit skin friction = 11.7 kpa (245 psf) Davidsons's Failure Line Load m 10.9 m 1.9 m Load, kn

25 Effects on End Bearing Shaft 2 (soft bottom) had 5-10% higher capacity than Shaft 4 (Structural defects) Undocumented variation in construction Mobilized Cu in End Bearing 51 kpa - Shaft kpa - Shaft 4 (Reload) Reloading caused 20% reduction 34.5 kpa - Shaft 2 soft bottom 4 months after construction 33% lower than virgin loading 20% lower than reloading

26 Effects on Skin Friction Mobilized Skin friction 17.4 kpa Shaft 2 virgin loading 11.7 kpa Shaft 4 reload 30% reduction Breakage of Cementation Remolding of Clay Structural Defects

27 Conclusions Soft bottom shaft had higher capacity Skin friction dominated capacity Soft bottom resulted in 33% reduction in capacity Undocumented differences in construction End Bearing Reloading: 20% reduction in capacity Soft Bottom: 33% reduction in capacity Skin Friction Reloading: 30% reduction in capacity Defects appear to have a small effect on capacity, but further research is needed.

28 Publications Ealy, C., M. Iskander, M. Justason, D. Winters, and G. Mullins (2002) Comparison Between Statnamic and Static Load Testing of Drilled Shafts in Varved Clay Proc. 9 th International Conference on Piling and Deep Foundations, Nice, June 3-5, 2002 Iskander, M., D. Roy, C. Ealy, and S. Kelley, (2001) Class-A Prediction of Construction Defects in Drilled Shafts, Journal of Transportation Research Board (formerly Transportation Research Records), No. 1772, pp , and Proc. Transportation Research Board Meeting, Jan. 7-13, CD, National Academy Press. Iskander, M., S. Kelley, C. Ealy, and D. Roy, (2001) Load Tests on Drilled Shafts with Planned Defects in Varved Clay, Proc. Transportation Research Board Meeting, Jan. 7-13, CD, National Academy Press. Iskander, M., D. Roy, and C. Ealy (2001) Results of the NDT Prediction Symposium of Construction Defects in Drilled Shafts, Foundation Drilling Magazine, ADSC, August Issue pp Iskander, M., and D. Roy (2000) Prediction of Defects and Capacity of Drilled Shafts in Varved clays, Foundation Drilling Magazine, ADSC, August Issue pp Iskander, M., D. Roy, C. Ealy, and S. Kelley, Drilled Shaft Defects, Detection and Effects in Varved Clay Submitted for Publication, ASCE Geotechnical and Geoenvironmental Journal

29 Acknowledgments Douglas Roy, PE Shawn Kelley, UMAS Jim Maxwell, Hub Foundation Company, Inc. Gill Peel, American Equipment and Fabricating Corporation A. Grey Mullen, USF Mike O Neill, U of H Pierre Gouvin, Rock Test Slope Indicator Company Rich Finno Northwestern University Carl Ealy, FHWA Al Dimillio, FHWA Scot Litke, ADSC Olson Engineering Construction Technologies Labratories (CTL) STS Consultants Geosciences Testing and Research S. Gassman, Univ. of South Carolina GZA Geoenvironmental Bob Mokowa, UMASS GRL Alan Lutenegger,UMASS B&A UMASS Students Polymer Drilling Systems Co. Polymer Drilling Systems Co. Geo Institute Deep Foundations Committee