dotd drilled shafts
Analysis of Drilled Shafts in Louisiana Philip Alan Goppelt April 27, 2012
Friday, April 27, 12
Why Drilled Shafts?
Friday, April 27, 12
❖
Large end bearing load resistance
❖
Large lateral load resistance
❖
May replace several piles
❖
No pile cap is needed
❖
Utilizes economical reinforced concrete
Example: DS-29
Friday, April 27, 12
❖
48 inches in diameter
❖
77 feet deep
❖
4000-ksi concrete
❖
“Stiff to hard silt and clay”
Example: DS-29
Friday, April 27, 12
Predicted and Actual Load vs. Settlement 1000
1999 FHWA Method 2010 FHWA Method Measured and Extrapolated
Load (tons)
800 600
Drilled Shaft #29 had an extrapolated bearing capacity that was moderately higher than the design value.
❖
Exemplary of the result we expect to get from the vast majority of drilled shafts.
400 200 0 0
1.5
3.0 Settlement (inches)
Friday, April 27, 12
❖
4.5
6.0
Calculation of Ultimate Bearing Capacity (UBC)
Friday, April 27, 12
❖
The goal of all UBC calculation methods is to find the resistance at an acceptable deflection (service deflection) or margin from the yield load.
❖
Methods covered: ❖
Three are based on settlement (relative or absolute).
❖
Two are based strictly on slope change.
❖
Two are offset methods.
❖
One falls into none of these categories.
Settlement Methods Diameter
5%B
4%B
Terzaghi and Peck 50
25
12.5
0
Friday, April 27, 12
Settlement (inches)
37.5
Terzaghi and Peck 1000
Load (tons)
800
Ultimate load is always at a settlement of 1 inch.
❖
Terzaghi, K., and Peck, R. B. (1967). Soil mechanics in engineering practice, 2nd Ed., Wiley, New York, 402.
600 400 200 0 0
1
2 Settlement (inches)
Friday, April 27, 12
❖
3
4
4%B and 5%B 1000
❖
Same loadsettlement diagram.
❖
B = shaft diameter.
❖
Ultimate load is found at the settlement equal to 4% or 5% of the diameter of the shaft.
❖
For #29, B = 4 feet.
Load (tons)
800 600 400 200 0 0
0.5
1.0
1.5
2.0
2.5
Settlement (inches) Friday, April 27, 12
3.0
3.5
4.0
L1 and L2 1000 ❖
The same loadsettlement curve is modeled as having two linear portions and a curved connecting portion.
❖
The end of the initial linear curve is L1. The beginning of the final linear curve is L2.
Load (tons)
800 600 400 200 0 0
1
2 Settlement (inches)
Friday, April 27, 12
3
4
DeBeer
Load (tons)
1000
100
10 0.001
0.010
0.100 Settlement (inches)
Friday, April 27, 12
1.000
10.000
❖
Same loadsettlement curve, but on a log-log scale.
❖
Ultimate load is at the change in slope on the curve.
❖
Works well when the change in slope is sharply defined.
Slope Tangent 1000
Load (tons)
800
Offset method
❖
Initial elastic slope, the same slope calculated for L1, is shifted by 0.15 in. + B/120.
❖
Intersection of slope and load-settlement curve is the point of ultimate load.
600 400 200 0 0
1
2 0.15 in. + B/120 = 0.55 in.
Friday, April 27, 12
❖
3
4
Modified Davisson D 930 in. = =0.00026 in./ton 6 AE 3.58*10 tons
Friday, April 27, 12
❖
Offset method, like the slope tangent method, with a line slope of D/AE
❖
D = shaft depth (for #29, 930 in.)
❖
A = shaft area (for #29, 1810 in.)
❖
E = shaft elastic modulus (for #29, 1977 tons per square inch)
❖
Line is shifted B/30.
Modified Davisson 1000
Load (tons)
800 600 400 200 0 0
1 B/30 = 1.6 in.
Friday, April 27, 12
2
3
4
Chin Settlement/Load (in./tons)
0.00500
Only method not based on a settlement or intersection of lines.
❖
Plots settlement/load, instead of load, as a function of settlement.
❖
Capacity is the inverse of the slope of a linear trendline fitted to the curve.
y = 0.0012x + 0.0001 R² = 0.9999
0.00375
0.00250
0.00125
0 0
1
2 Settlement (inches)
Friday, April 27, 12
❖
3
4
1 =833 tons 0.0012
Ultimate Bearing Capacity from the Measured/Extrapolated Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Summary ❖
❖
❖
Design of drilled shafts is based on many factors, including local soil conditions. It is wise to calibrate resistance factors for local soil conditions. LTRC analyzed twenty-six “old” drilled shafts and released a report in 2010 with a recommended φ factor of 0.5 for mixed soils. LTRC is preparing another report that adds eight “new” drilled shafts and lowers φ to 0.4. Our goal is to give bridge engineers guidance on the proper resistance factors to use to achieve a reliability index of 3.0.
Design
LTRC Research
Bridge Engineers
Analysis
❖
For this project capsule, please see http://www.ltrc.lsu.edu/pdf/2011/capsule_11-4GT.pdf
❖
For the old report, please see http://www.ltrc.lsu.edu/pdf/2010/fr_470.pdf
Friday, April 27, 12
References ❖
No. 132014, N H I Course. “Drilled shafts: Construction procedures and design methods.” Ed. D A Brown, J P Turner, & R J Castelli. Tunnelling and Underground Space Technology 5.1-2 (2010) : 156-157.
❖
Abu-Farsakh, M.Y., X. Yu et al. “Calibration of Resistance Factors Needed in the LRFD Design of Drilled Shafts.” (2010)
❖
Abu-Farsakh, M.Y., S. Yoon et al. “Calibration of Resistance Factors Needed in the LRFD Design of Drilled Shafts.” (2012)
❖
Abu-Farsakh, M.Y., and X. Yu. “Interpretation Criteria to Evaluate Resistance Factors for Axial Load Capacity of Drilled Shafts.” Transportation Research Record: Journal of the Transportation Research Board 2202.1 (2010): 20-31.
❖
Chen, Y.J., and Y.C. Fang. “Critical Evaluation of Compression Interpretation Criteria for Drilled Shafts.” Journal of geotechnical and geoenvironmental engineering 135 (2009): 1056.
❖
“Conduct and Interpretation of Load Tests on Drilled Shaft Foundations. Volume 1: Detailed Guidelines.” Cornell University Geotechnical Engineering Group, July 1988. Web. 25 Apr. 2012.
❖
“Report on Drilled Shaft Load Testing (Osterberg Method). TS #4 - I-10 Widening - Siegen Lane Bent 3. Baton Rouge, LA (L-9459-4)” LOADTEST, Inc. 7 Oct. 2009.
❖
“Osterberg Cell.” Loadtest, Inc. Web 27 Apr. 2012.
❖
“Drilled Shaft Construction – Part 2,” The National Driller, Oct. 2004. Web. 24 Apr. 2012.
❖
“Driven Piles,” Hayward Baker Geotechnical Construction. Web. 24 Apr. 2012.
❖
“Section 3. Drilled Shafts,” Texas DOT 2006 Geotechnical Manual, 01 Aug. 2006. Web. 24 Apr. 2012.
❖
“Chapter 2. What Is a Drilled Shaft?,” Florida DOT Drilled Shaft Inspector Tutorial. Web. 24 Apr. 2012.
❖
Mullins, Gray, Ph.D., P.E. “Drilled Shafts,” University of South Florida. Web. 24 Apr. 2012.
❖
Rao, Varanasi Rama. “PILE FOUNDATIONS.” 03 Apr. 2009. Web. 25 Apr. 2012.
Friday, April 27, 12
Thank You
❖
Friday, April 27, 12
Any questions or comments?
Ultimate Bearing Capacity from the Old FHWA Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Ultimate Bearing Capacity from the New FHWA Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Ultimate Bearing Capacity from the Measured/Extrapolated Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Friday, April 27, 12
Why Drilled Shafts?
Friday, April 27, 12
❖
Large end bearing load resistance
❖
Large lateral load resistance
❖
May replace several piles
❖
No pile cap is needed
❖
Utilizes economical reinforced concrete
Example: DS-29
Friday, April 27, 12
❖
48 inches in diameter
❖
77 feet deep
❖
4000-ksi concrete
❖
“Stiff to hard silt and clay”
Example: DS-29
Friday, April 27, 12
Predicted and Actual Load vs. Settlement 1000
1999 FHWA Method 2010 FHWA Method Measured and Extrapolated
Load (tons)
800 600
Drilled Shaft #29 had an extrapolated bearing capacity that was moderately higher than the design value.
❖
Exemplary of the result we expect to get from the vast majority of drilled shafts.
400 200 0 0
1.5
3.0 Settlement (inches)
Friday, April 27, 12
❖
4.5
6.0
Calculation of Ultimate Bearing Capacity (UBC)
Friday, April 27, 12
❖
The goal of all UBC calculation methods is to find the resistance at an acceptable deflection (service deflection) or margin from the yield load.
❖
Methods covered: ❖
Three are based on settlement (relative or absolute).
❖
Two are based strictly on slope change.
❖
Two are offset methods.
❖
One falls into none of these categories.
Settlement Methods Diameter
5%B
4%B
Terzaghi and Peck 50
25
12.5
0
Friday, April 27, 12
Settlement (inches)
37.5
Terzaghi and Peck 1000
Load (tons)
800
Ultimate load is always at a settlement of 1 inch.
❖
Terzaghi, K., and Peck, R. B. (1967). Soil mechanics in engineering practice, 2nd Ed., Wiley, New York, 402.
600 400 200 0 0
1
2 Settlement (inches)
Friday, April 27, 12
❖
3
4
4%B and 5%B 1000
❖
Same loadsettlement diagram.
❖
B = shaft diameter.
❖
Ultimate load is found at the settlement equal to 4% or 5% of the diameter of the shaft.
❖
For #29, B = 4 feet.
Load (tons)
800 600 400 200 0 0
0.5
1.0
1.5
2.0
2.5
Settlement (inches) Friday, April 27, 12
3.0
3.5
4.0
L1 and L2 1000 ❖
The same loadsettlement curve is modeled as having two linear portions and a curved connecting portion.
❖
The end of the initial linear curve is L1. The beginning of the final linear curve is L2.
Load (tons)
800 600 400 200 0 0
1
2 Settlement (inches)
Friday, April 27, 12
3
4
DeBeer
Load (tons)
1000
100
10 0.001
0.010
0.100 Settlement (inches)
Friday, April 27, 12
1.000
10.000
❖
Same loadsettlement curve, but on a log-log scale.
❖
Ultimate load is at the change in slope on the curve.
❖
Works well when the change in slope is sharply defined.
Slope Tangent 1000
Load (tons)
800
Offset method
❖
Initial elastic slope, the same slope calculated for L1, is shifted by 0.15 in. + B/120.
❖
Intersection of slope and load-settlement curve is the point of ultimate load.
600 400 200 0 0
1
2 0.15 in. + B/120 = 0.55 in.
Friday, April 27, 12
❖
3
4
Modified Davisson D 930 in. = =0.00026 in./ton 6 AE 3.58*10 tons
Friday, April 27, 12
❖
Offset method, like the slope tangent method, with a line slope of D/AE
❖
D = shaft depth (for #29, 930 in.)
❖
A = shaft area (for #29, 1810 in.)
❖
E = shaft elastic modulus (for #29, 1977 tons per square inch)
❖
Line is shifted B/30.
Modified Davisson 1000
Load (tons)
800 600 400 200 0 0
1 B/30 = 1.6 in.
Friday, April 27, 12
2
3
4
Chin Settlement/Load (in./tons)
0.00500
Only method not based on a settlement or intersection of lines.
❖
Plots settlement/load, instead of load, as a function of settlement.
❖
Capacity is the inverse of the slope of a linear trendline fitted to the curve.
y = 0.0012x + 0.0001 R² = 0.9999
0.00375
0.00250
0.00125
0 0
1
2 Settlement (inches)
Friday, April 27, 12
❖
3
4
1 =833 tons 0.0012
Ultimate Bearing Capacity from the Measured/Extrapolated Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Summary ❖
❖
❖
Design of drilled shafts is based on many factors, including local soil conditions. It is wise to calibrate resistance factors for local soil conditions. LTRC analyzed twenty-six “old” drilled shafts and released a report in 2010 with a recommended φ factor of 0.5 for mixed soils. LTRC is preparing another report that adds eight “new” drilled shafts and lowers φ to 0.4. Our goal is to give bridge engineers guidance on the proper resistance factors to use to achieve a reliability index of 3.0.
Design
LTRC Research
Bridge Engineers
Analysis
❖
For this project capsule, please see http://www.ltrc.lsu.edu/pdf/2011/capsule_11-4GT.pdf
❖
For the old report, please see http://www.ltrc.lsu.edu/pdf/2010/fr_470.pdf
Friday, April 27, 12
References ❖
No. 132014, N H I Course. “Drilled shafts: Construction procedures and design methods.” Ed. D A Brown, J P Turner, & R J Castelli. Tunnelling and Underground Space Technology 5.1-2 (2010) : 156-157.
❖
Abu-Farsakh, M.Y., X. Yu et al. “Calibration of Resistance Factors Needed in the LRFD Design of Drilled Shafts.” (2010)
❖
Abu-Farsakh, M.Y., S. Yoon et al. “Calibration of Resistance Factors Needed in the LRFD Design of Drilled Shafts.” (2012)
❖
Abu-Farsakh, M.Y., and X. Yu. “Interpretation Criteria to Evaluate Resistance Factors for Axial Load Capacity of Drilled Shafts.” Transportation Research Record: Journal of the Transportation Research Board 2202.1 (2010): 20-31.
❖
Chen, Y.J., and Y.C. Fang. “Critical Evaluation of Compression Interpretation Criteria for Drilled Shafts.” Journal of geotechnical and geoenvironmental engineering 135 (2009): 1056.
❖
“Conduct and Interpretation of Load Tests on Drilled Shaft Foundations. Volume 1: Detailed Guidelines.” Cornell University Geotechnical Engineering Group, July 1988. Web. 25 Apr. 2012.
❖
“Report on Drilled Shaft Load Testing (Osterberg Method). TS #4 - I-10 Widening - Siegen Lane Bent 3. Baton Rouge, LA (L-9459-4)” LOADTEST, Inc. 7 Oct. 2009.
❖
“Osterberg Cell.” Loadtest, Inc. Web 27 Apr. 2012.
❖
“Drilled Shaft Construction – Part 2,” The National Driller, Oct. 2004. Web. 24 Apr. 2012.
❖
“Driven Piles,” Hayward Baker Geotechnical Construction. Web. 24 Apr. 2012.
❖
“Section 3. Drilled Shafts,” Texas DOT 2006 Geotechnical Manual, 01 Aug. 2006. Web. 24 Apr. 2012.
❖
“Chapter 2. What Is a Drilled Shaft?,” Florida DOT Drilled Shaft Inspector Tutorial. Web. 24 Apr. 2012.
❖
Mullins, Gray, Ph.D., P.E. “Drilled Shafts,” University of South Florida. Web. 24 Apr. 2012.
❖
Rao, Varanasi Rama. “PILE FOUNDATIONS.” 03 Apr. 2009. Web. 25 Apr. 2012.
Friday, April 27, 12
Thank You
❖
Friday, April 27, 12
Any questions or comments?
Ultimate Bearing Capacity from the Old FHWA Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Ultimate Bearing Capacity from the New FHWA Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
Ultimate Bearing Capacity from the Measured/Extrapolated Curve 1,000
Terzaghi and Peck 4%B 5%B L1 L2 DeBeer Slope Tangent Modified Davisson Chin
750 500 250 0
Units are in tons. Friday, April 27, 12
