PJA Drilled Shaft Design For Constructability - Dan Brown And Associates

Dan Brown and Assoc., PLLC Construction Considerations in the Selection and Design of Drilled Shaft Foundations for Bridges By: Paul Axtell, P.E. Dan Brown and Associates, PLLC www.danbrownandassociates.com Overview Drilled Shaft Applications for Bridges New Machines and Capabilities Slurry Advancements Design of Rock Sockets Base Resistance Concrete & Reinforcing 1

Dan Brown and Assoc., PLLC Characteristics of Bridge Foundations Congested sites, existing structures & utilities Many y equipment q p moves & difficult access Owner specifications & review, often in a design-build environment Extensive performance verification; structural integrity and axial resistance How do we build it? Drilled Shaft Applications Bridges where small footprint is needed Usually minimal impact on nearby structures 1-2-4 2

Dan Brown and Assoc., PLLC Drilled Shaft Applications Bridges constructed over water; single g shaft p per column may y avoid cofferdam 1-2-5 Drilled Shaft Applications Very large foundation loads 1-2-6 3

Dan Brown and Assoc., PLLC Drilled Shaft Applications Foundations with deep scour or potential liquefaction, lateral spreading 1-2-7 Larger, More Powerful Machines 4

Dan Brown and Assoc., PLLC Influence of Slurry on Axial Resistance Displacement (mm) 0 -10 -20 20 -30 -40 Bentonite Shaft -50 Polymer Shaft -60 0 Data from Auburn University 2 4 6 8 Load (MN) 10 12 14 Data from Cape p Fear Bridge, g , Wilmington, g , NC Rock Sockets Rock excavation can be expensive Structural capacity of shaft may govern design Axial: End bearing side shear Lateral: Perform sensitivity analysis 5

Dan Brown and Assoc., PLLC Rock Socket – Axial Ductility of Side Shear Resistance C Combined R Resistance B A Base Side Butt Displacement Load vs. Displacement from Statnamic Test Tampa, Florida Side Shear vs Displacement from Statnamic Test Segment 3 (38.25 ft to -50.25 ft) Limestone Tampa, Florida -0.50 -1.50 -2.00 -2.50 0 500 1000 1500 Load (kips) 2000 2500 3000 Segm ment Displacement (inches) 0 -1.00 -0.5 Maximum Side Shear in Limestone Socket 15.5 ksf @ 1.4 inches of displacement. Approximate yeild point 13.4 ksf at 0.29 inches of displacement (tangent approximation). -1 -1 5 -1.5 -2 0 2 4 6 8 10 12 14 16 Side Shear (ksf) End Bearing Load vs. Toe Displacement from Statnamic Test; Tampa, Florida 0.00 Toe Displacement (inch hes) Displacement (inches) 0.00 0 50 -0.50 -1.00 -1.50 -2.00 Note: Includes 2 ' of side shear -2.50 0 200 400 600 800 1000 1200 Load (kips) 6

Dan Brown and Assoc., PLLC Rock Sockets - Lateral 0 0 -10 -10 Sand Depth, ft Depth, ft Sand -20 -30 -20 -30 3’ Socket -40 -40 Rock -50 -0.5 Rock 10’ Socket 0.0 0.5 1.0 1.5 -50 -20000 Deflection, inches 0 20000 40000 60000 Moment, inch-kips 6’ Dia. Shaft 40’ Lse to Med Dse Sand over Sandstone (500psi qu) Bottom Cleanout & Inspection Techniques for slurry or underwater construction 7

Dan Brown and Assoc., PLLC Base Resistance & Cleanliness It is possible to get a reasonably clean base under water or slurry It is not possible to get a perfectly clean base in any circumstances Attempts to require a “dry hole” for end bearing may be counterproductive Lumber River Test Shaft Base Resistance in Sands Cohesionless sands may never indicate sound base Base grouting can be very effective to enhance base resistance & QA 8

Dan Brown and Assoc., PLLC Base Grouting Enhance Axial Resistance Improve Reliability Mitigate Imperfections in Base Conditions The Base Grouting Process 2. Base Grout Pressure Constructed Applied 1. Shaft 3. Some Relaxation Occurs 4. Structural Load Applied 9

Dan Brown and Assoc., PLLC Base Grouting Apparatus Tube á Manchette Cover Plate (using CSL tubes) CSL Tube Criteria Target Pressure Minimum Net Volume Limit Upward Shaft Movement Exhumed Shaft 10

Dan Brown and Assoc., PLLC Huey Long Bridge, New Orleans Huey Long Bridge, New Orleans 131ksf 11

Dan Brown and Assoc., PLLC John James Audubon Bridge, La. O-Cell Load (tons) 0 500 1,000 1,500 2,000 2,500 3,000 3,500 0.00 Downward Displacement (inches) . Base Grouted 136ksf 1.00 2.00 NOT Base Grouted 3.00 4 00 4.00 5.00 Shaft 11W Load Test Shaft 11E Load Test Shaft T2 Load Test Shaft 15E Load Test Shaft T4 Load Test Shaft T3 Load Test Concrete & Reinforcing Constructability Issues that can be significantly reduced during structural design Workability and passing ability of concrete Reinforcing cage congestion Time required to place cage and concrete (full slurry exchange) Our slurry specs aren’t tight enough for large shafts 12

Dan Brown and Assoc., PLLC Structural Design of Drilled Shafts AASHTO (Article 10.8.3.9.1) : ‘The The structural design of drilled shafts shall be in accordance with the provisions of Section 5 for the design of reinforced concrete’ But . . . with adequate consideration of drilled shaft constructability Drilled Shaft Concrete Unique Requirements Workability Workability Retention Passing ability Segregation resistance Bleeding characteristics Heat of hydration (in large diameter shafts) 13

Dan Brown and Assoc., PLLC Need for Workability and Passing Ability tremie rebar concrete Congested Cage, Concrete with inadequate workability Concrete with good workability and filling ability Potential Problem w/ Inadequate Concrete Workability Tremie Slurry Fresh, F h fluid fl id concrete t Trapped Laitance Old, stiff concrete 14

Dan Brown and Assoc., PLLC Characteristics of HPDSC (High Performance Drilled Shaft Concrete) 18”-24” Slump Flow Smaller, Rounded Coarse Aggregate Increased Sand/Coarse Agg. Ratio Supplementary cementing materials (SCM) Flyy ash Slag cement Extensive use of chemical admixtures Chemical Admixtures Air-Entraining Admixture Set-Controlling Admixture – – Retarder Hydration stabilizer (Type D) Water Reducing Admixture Viscosity Modifying Admixture (VMA) 15

Dan Brown and Assoc., PLLC Lumber River, Coastal South Carolina Constituent Value Type I/II Cement 500 pcy y Ash Class F Fly 250 p pcy y Sand 1366 pcy #67 Gravel 1071 pcy #789 Gravel 395 pcy Water 306 pcy w/cm 0.41 Air 2% Delvo Stabilizer 8 oz/cwt Glenium 3030 NS 8-12 oz/cwt Rheomax VMA 358 2 oz/cwt Slump Flow 18”-24” Mullica River, Atlantic City, NJ Constituent Value Type I Cement 526 pcy Class F Fly Ash 132 pcy Sand 1363 pcy #8” CA 1500 pcy Water 267 pcy w/cm 0.405 Air 7.5% HRWRA (Sika 2100 SP) 7 oz/cwt Retarder/Water Reducer (Sika Plastiment) 4 oz/cwt Spread 18”-24” 16

Dan Brown and Assoc., PLLC Strategies for Constructable Cages Use larger diameter shaft It’s a compromise (big openings big bars; small bars for durability). Reduce reinforcement below high moment Bundle bars (hoops, too) to increase openings Use permanent casing for confinement (instead of tight spirals) Use 6” cover for tolerance to match column Locate column splice above pour cutoff Congested Rebar Cage 17

Dan Brown and Assoc., PLLC Constructability Problems with Congested Reinforcing Cages Essentials of Cage Design for Constructability Clear Spacing Between All Bars 5 D of Largest Coarse Aggregate or 6 inches, (whichever is larger) Use Only Lap or Mechanical Splices Locate Splices As Deep As Possible 18

Dan Brown and Assoc., PLLC Limits on Longitudinal Steel AASHTO 5.7.4.2: 1% ρs 8% A s fy A g fc' 0.135 Seismic Zones 2, 3, and 4: ρs 6% Practical Limits for Drilled Shafts Typically: 1% ρs 2% High seismic: 2% ρs 3% As the value of ρs approaches 4% it becomes impossible to ensure flow of concrete and should be avoided (constructability) For axial loading only, when cross-section is larger than required: minimum ρs 0.5% 19

Dan Brown and Assoc., PLLC Bundle Bars Partial Length Cage 20

Dan Brown and Assoc., PLLC Permanent Casing Often exists to help with constructability, particularly for water crossing bridges Provides confinement Increases flexural stiffness and capacity Consider corrosion losses Not fully utilized near ends of casing Summary Bigger shafts are possible Count on base and side resistance may avoid need for coffer dam may reduce impact on adjacent structures demonstrate with load test reduces socket length g don’t get carried away with lateral design Concrete & reinforcing designed considering constructability 21

Dan Brown and Assoc., PLLC Thanks for Listening! 22

Structural Design of Drilled Shafts AASHTO (Article 10.8.3.9.1) : 'The structural design of drilled shafts shall beThe structural design of drilled shafts shall be in accordance with the provisions of Section 5 for the design of reinforced concrete' But . . . with adequate consideration of drilled shaft constructability Drilled Shaft Concrete