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 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?

Research Methods Geometric Scale Factor, λ 1:1 1:~8 1:~100 Field Testing Centrifuge Testing Large- Actual Reproduce stresses, performance, but but scale -no control of -cannot model environmental construction Physical conditions techniques -remote test sites -member/soil Modeling interaction -failure data rare questionable

Modeling Device

Model Container

Model Soil Zero Air Voids 120 Reduced Proctor 115 Liquid Limit 23 110 γ d (lb/ft 3 ) Plastic Limit 14 105 Plasticity Index 9 100 Organic Content 1% 95 6% 8% 10% 12% 14% 16% 18% 20% ω Fines Content 19% Grain Size (inch) 1 0.1 0.01 0.001 0.0001 100% γ d-max 115 pcf Percent Finer by Dry Weight 80% w opt 13% 60% 40% φ ’ 33 o 20% 0% 10 1 0.1 0.01 Grain Size (mm)

Pore Pressure Control System Sprinkler System

Instrumentation: Pore Pressure

Instrumentation: Displacement

Reinforcement & Similitude � Can’t scale stresses, but can scale reinforcement stiffness appropriately: 4” 2.5” 0.75” 0.28” λ = 8 0.3” 0.1” λ EI = 1,448 EI = 2,200 lb-ft 2 EI = 3.65x10 6 lb-ft 2

Instrumentation: Strain Gages

Construction

Construction: Model Micropiles

Construction: Model Micropiles

As-constructed

Testing

Failure!

Time Lapse Movie Clip

Model Performance – pore pressures 150 24 30 32 34 36 38 40 42 44 45 100 50 3 0 4 9 Pore Pressure (psf) -50 1 5 -100 -150 2 -200 6 7 8 -250 -300 -350 -400 0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 Elapsed Time (Hours)

Model Behavior - deformations 10 24 30 32 34 36 40 42 44 45 38 9 8 7 Displacement (inches) 6 5 5 6 8 4 3 7 2 9 1 1 4 0 2 3 -1 0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384 408 Elapsed Time (hours)

Forensics

Forensics

Interpretation of Results 2.4 2.4 U2 U2 2.2 2.2 U3 U3 U4 2.0 2.0 U4 Factor of Safety Factor of Safety 1.8 1.8 1.6 1.6 1.4 1.4 1.2 1.2 1.0 1.0 0.8 0.8 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 22 25 28 31 34 37 40 43 46 Slope Face Angle Slope Displacement (in.)

Moment Distribution 30 30 38 Distance from Micropile Bottom (in) 25 45 20 15 10 5 0 -5 0 5 10 15 20 25 Moment (lb-in)

Load Transfer 24 Maximum Induced Bending Moment (lb-in) 20 R1, S/D = 29.3 R2, S/D = 14.7 R3, S/D = 9.8 16 12 8 4 0 24 27 30 33 36 39 42 45 48 Inclination (Degrees)

Completed Testing � Unreinforced models � 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

Future Testing � A-frame arrangement with capping beam � Reticulated micropile � Larger scale device

Observations � Tests performed for unreinforced slopes indicate modeling errors are small � Model micropiles reasonably representative of field scale micropiles � Mobilization of resistance is roughly linear � Capping beam necessary for conditions tested to date

Acknowledgements � Funding provided by U.S. National Science Foundation, Grant CMS0093164