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Large-scale Physical Model Tests
- f Micropile Stabilized Slopes
- J. Erik Loehr and Andrew Boeckmann
Large-scale Physical Model Tests of Micropile Stabilized Slopes J. - - PowerPoint PPT Presentation
Large-scale Physical Model Tests of Micropile Stabilized Slopes J. - - PowerPoint PPT Presentation
Large-scale Physical Model Tests of Micropile Stabilized Slopes J. Erik Loehr and Andrew Boeckmann University of Missouri Columbia John J. Deeken Black and Veatch Stabilization Technique Motivation How is force developed within
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Motivation
How is force developed within reinforcing
members?
What is the interaction between the soil and
the reinforcing members?
How does geometric arrangement affect load
transfer and limit loads?
What group or network effects exist?
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Research Methods
Geometric Scale Factor, λ 1:1 1:~8 1:~100 Field Testing
Large- scale Physical Modeling
Centrifuge Testing
Actual performance, but
- no control of
environmental conditions
- remote test sites
- failure data rare
Reproduce stresses, but
- cannot model
construction techniques
- member/soil
interaction questionable
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Modeling Device
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Model Container
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Model Soil
33o φ’ 13% wopt 115 pcf γd-max 19% Fines Content 1% Organic Content 9 Plasticity Index 14 Plastic Limit 23 Liquid Limit
95 100 105 110 115 120 6% 8% 10% 12% 14% 16% 18% 20% ω γd (lb/ft3) Zero Air Voids Reduced Proctor 0% 20% 40% 60% 80% 100% 0.01 0.1 1 10 Grain Size (mm) Percent Finer by Dry Weight 0.0001 0.001 0.01 0.1 1 Grain Size (inch)
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Pore Pressure Control System
Sprinkler System
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Instrumentation: Pore Pressure
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Instrumentation: Displacement
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Reinforcement & Similitude
Can’t scale stresses, but can scale
reinforcement stiffness appropriately:
λ = 8 λEI = 1,448 EI = 3.65x106 lb-ft2 4” 2.5” 0.3” 0.75” 0.28” 0.1” EI = 2,200 lb-ft2
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Instrumentation: Strain Gages
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Construction
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Construction: Model Micropiles
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Construction: Model Micropiles
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As-constructed
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Testing
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Failure!
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Time Lapse Movie Clip
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Model Performance – pore pressures
- 400
- 350
- 300
- 250
- 200
- 150
- 100
- 50
50 100 150 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 Elapsed Time (Hours) Pore Pressure (psf) 3 4 1 6 8 5 2 7 9 24 30 32 34 36 38 40 42 44 45
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Model Behavior - deformations
- 1
1 2 3 4 5 6 7 8 9 10 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 Elapsed Time (hours) Displacement (inches) 2 6 7 4 3 5 9 1 8 24 30 32 34 36 38 40 42 44 45
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Forensics
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Forensics
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Interpretation of Results
0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 22 25 28 31 34 37 40 43 46 Slope Face Angle Factor of Safety U2 U3 U4 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Slope Displacement (in.) Factor of Safety U2 U3 U4
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Moment Distribution
5 10 15 20 25 30
- 5
5 10 15 20 25 Moment (lb-in) Distance from Micropile Bottom (in) 30 38 45
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Load Transfer
4 8 12 16 20 24 24 27 30 33 36 39 42 45 48 Inclination (Degrees) Maximum Induced Bending Moment (lb-in) R1, S/D = 29.3 R2, S/D = 14.7 R3, S/D = 9.8
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Completed Testing
Single Line, Perpendicular to Slope
- s/d from 8 to 30
- “rigid” and scaled
members
Single Line, A-Frame
- s/d from 4 to 8
- No cap beam
Unreinforced models
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Future Testing
A-frame arrangement with capping
beam
Reticulated micropile Larger scale device
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Observations
Tests performed for unreinforced slopes
indicate modeling errors are small
Model micropiles reasonably representative
- f field scale micropiles
Mobilization of resistance is roughly linear Capping beam necessary for conditions
tested to date
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Acknowledgements
Funding provided by U.S. National Science