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USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL

USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL. The design is not complete until the last pile is driven. Uncertainty is Inherent in Soil Sampling. Uncertainty ??. 0.00000005 % of soil volume is explored. Soil tested is even smaller percent of soils

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USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL

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  1. USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL

  2. The design is not complete until the last pile is driven.

  3. Uncertainty is Inherent in Soil Sampling

  4. Uncertainty ?? • 0.00000005 % of soil volume is explored. • Soil tested is even smaller percent of soils • Soil disturbance lowers soil strength. • Soil and bedrock conditions are random

  5. How Do We Reduce Uncertainty? • Subsurface Exploration of Soil and Bedrock Conditions • Borings • CPTs • Test shafts • Geophysical Exploration • Drive Indicator Piles • Dynamic Testing • Load Testing

  6. When to Perform a Load Test • Large project where small savings on length is a large monetary savings. • Project cost is critical. • Structure is very sensitive to settlement. • Critical Structure with high loads i.e. bridge. • Engineer lacks experienced in the area. • Piles must resist uplift.

  7. How Design Can Increase Costs • Analytical capacity is often conservative. • Pile length increased for unknowns. • High factor of safety used.

  8. Calculations Conservative • Some engineers use soil property estimates from a Design Manual which are generally conservative. • The size of the geotechnical exploration budget can affect how conservative the design is. • Most agencies are conservative.

  9. Adding Extra Pile Length • Some engineers will arbitrarily increase the pile lengths just to be on the safe side. • Added pile length is the most expensive part of the pile when driving into dense or hard materials.

  10. Factor of Safety • The size of the factor of safety reflects the uncertainty of the soil conditions and the pile capacity. • If the uncertainty is reduced it is appropriate to reduce the factor of safety. i.e. from 3.0 to 2.0

  11. Benefits of Rapid Load Tests • Uncertainty is reduced with multiple tests. • Soil Parameters used in Calculations checked. • Factor of safety may be reduced. • Pile lengths may be reduced. • Cost savings from reduced pile lengths and driving time.

  12. Load Testing Methods

  13. Static Load Test(Compression)

  14. Tension ASTM D 1143 Load Cell (Load) Reinforcing Bars Test Frame Wooden Planks Wooden Planks Test Pile Dial Indicators (deformation) Ca Subsurface Soils

  15. Rapid Load Tests

  16. Statnamic Single Point Test Rapid Load Test Rapid Load Tests

  17. Statnamic Signal Point Load Test Gravel Container Gravel Masses Combustion Chamber Pile

  18. Statnamic Load Test Apparatus

  19. The RLT Drop Weight Rapid Load Tester Hydraulic Clamp Leads 25 kg Weight Damping Springs Test Pile

  20. Rapid Load Test System • MOBILE TESTING UNIT CAPABLE OF 6 TO 10 COMPRESSION TESTS/DAY • UP TO 800 KIP LOADING CAPABILITY • IMMEDIATE REPORTING • SELF-SUFFICIENT TESTING UNIT

  21. RLT Procedure • 25,000 kg mass dropped on pile from varying heights • Deflection Measured @ Point of Impact • Force applied to pile top for 200-ms duration • Energy transmitted to pile via anvil and dampened via springs • Springs recoil and push load up to unload pile

  22. Displacement Measurement System Load Cell LEDTransmitter DATA AQUISION SYSTEM

  23. Optical Receiver

  24. Plotting Test Results • Family of curves from individual drops is compiled to create classic “Load Deflection Curve”

  25. Hydraulic Clamp 25 kg Weight Damping Springs Receiver Load Cell LEDs Test Pile

  26. Load time Displacement Raw Data

  27. Case Histories Five Tests Sites

  28. Auger Cast Pile Load Test • 16-Inch Auger Cast Pile • 62’ Pile length • Tip of Pile Five Feet Into Dense Gravel Location: Sacramento Fill Sandy Silt Dense Sand Dense Gravel

  29. Static vs. Rapid Load Curves

  30. Case 2- Rotterdam • 400-mm Square Pile • 17 meters Long • End Bearing into Sand Fill Soft CL Dense Sand

  31. Static vs Pseudo-Static

  32. Case 3 – San Francisco • 22-Inch Diameter Tubex Pile • 60 Feet Deep • End-Bearing Into Dense Sand FILL Dense SM BAY MUD CH V. Dense SM Location : Fisherman’s Wharf , San Francisco

  33. Installing 16- inch Diameter Tubex Test Pile

  34. Static Test vs. Rapid Load Test Results Static Rapid Load Test Cohesionless Soil - Sand

  35. Case 4 - 24 Inch Diameter CIDH Piles • Capacity of Existing and new CIDH Piles • Performance Based Design • Results Correlated to Static Test • Refined Conventional CIDH Design • Location: U.C. Berkeley

  36. Static vs. Rapid Load Curves24 Inch CIDH Piers – Cohesive Soil Static Rapid Load Test

  37. Case 5 14-Inch Square Concrete Piles • 13 compression tests • Completed in 2 shifts • 3 static tension tests • Savings $500,000 • Location: Emeryville

  38. Typical Soil Profile No. 16” Square Pile Soil Type g (pcf)f(deg)C (psf) Ca/C 115 20 0 NA 110 5 200 0.9 125 20/24.5/28.6* 400/500/600* 0.9 130 24/27.9/32.5* 600/750/900* 0.8 130 27/32.5/37.4* 1000/1250/1500* 0.75 10’ 35’ 10’ 18’ Fill: (pre-drilled) Soft - Silty Clay Firm Sandy Clay Stiff Sandy Clay V. Stiff Sandy Clay 1 2 3 4 5 86’

  39. 15-test Pile Locations 3 Uplift – Load Tests 400’ 12 Rapid Load Tests 900’

  40. Rapid Load Test and Theory Load, kips 1 2 3 4 5 6 7 8 All Load Test Data 0.2 0.4 0.6 0.8 1.0 Deflection, In. Theoretical Capacity Load curve correction for clay

  41. Uplift Test Analysis & Results 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 All Load Test Data Deflection, In. Theoretical Capacity 0.0 50 100 150 200 250 300 350 400 Uplift Load, kips

  42. Rapid Load Tests in Clay • Rapid load test in clay yields higher capacity than a static test due to relaxation • Rapid load simulates seismic loading • Correction factor for clay – Prapid /Pstatic= 1.7

  43. Pile Load Testing Issues

  44. Factors Affecting a A Low Test Result • Excess Load Demand • Load Test Workmanship • Test Pile Location • Time After Pile Driven

  45. Look for Hidden Excess Load Demand in Pile Groups Column Load = 175 kips Allowable Pile Load = 110 kips Two piles required Capacity of pile cap = 220 kips Excess Capacity = 220 – 175 = 45 kips Actual ultimate capacity needed 175 / 2.0 = 87.5 x 2.0 = 175 kips/pile instead of 220 kips/pile

  46. Load Test Workmanship • Many Factors Can Effect Test Results • Is top of Pile level? • Was test stopped and started for some reason? • Were readings taken accurately? • Was pile damaged during driving? • Have gauges been calibrated?

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