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USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL.

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Presentation on theme: "USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL."— Presentation transcript:

1 USING THE RAPID LOAD TESTER TO PROVIDE PROJECT QUALITY CONTROL

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3 Uncertainty is Inherent in Soil Sampling

4  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  Subsurface Exploration of Soil and Bedrock Conditions  Borings  CPTs  Test shafts  Geophysical Exploration  Drive Indicator Piles  Dynamic Testing  Load Testing

6  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  Analytical capacity is often conservative.  Pile length increased for unknowns.  High factor of safety used.

8  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  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  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  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.

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

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16 Statnamic Single Point Test Rapid Load Test

17 Gravel Container Gravel Masses Combustion Chamber Pile

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

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

22  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

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25 Displacement Measurement System LED Transmitter DATA AQUISION SYSTEM Load Cell

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27  Family of curves from individual drops is compiled to create classic “Load Deflection Curve”

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

29 time Load Displacement Raw Data

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31 Case Histories

32  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

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34  400-mm Square Pile  17 meters Long  End Bearing into Sand Fill Soft CL Dense Sand

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36  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

37 Installing 16- inch Diameter Tubex Test Pile

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

39 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

40 Static vs. Rapid Load Curves 24 Inch CIDH Piers – Cohesive Soil Static Rapid Load Test

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

42 Fill: (pre-drilled) Soft - Silty Clay Firm Sandy Clay Stiff Sandy Clay V. Stiff Sandy Clay 10’ 35’ 10’ 18’ 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 No. 16” Square Pile Soil Type  (pcf)  (deg) C (psf) Ca/C 1234512345 86’

43 900’ 400’ 12 Rapid Load Tests 3 Uplift – Load Tests

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

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

46  Rapid load test in clay yields higher capacity than a static test due to relaxation  Rapid load simulates seismic loading  Correction factor for clay – P rapid /P static = 1.7

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48  Excess Load Demand  Load Test Workmanship  Test Pile Location  Time After Pile Driven

49 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

50  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?

51  Readings taken at 100 kip increments only.  Data between last 100 kip reading and ultimate load missing.  Always take as much data as possible.  Run test past design load to Davisson Criteria ultimate capacity

52 APPLIED LOAD Test Stopped Here Actual Ultimate Capacity DEFLECTION

53  Determine if there is an anomaly in the location of lower capacity test(s).  If so assign a lower allowable load in that area only.

54 1 10 100 1000 Hours After Installation 0 50 90 Percent of Capacity

55  The term “test failure” indicates the pile is useless or design values are wrong.  Analytical capacities are “best estimates”  Better to Use “Load Test Results”  The owner may be able to live with a lower design capacity

56  Inexperienced inspectors tend to overdrive piles looking for blow counts.  Load tests can minimize reliance on blow counts  Have a preconstruction meeting with engineer and agree on blow count criteria.

57 THE END


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