Outline of Presentation. Behavior of Laterally Loaded Piles in A Mechanically Stabilized Earth (MSE) Wall

Transcription

1 Behavior of Laterally Loaded Piles in A Mechanically Stabilized Earth (MSE) Wall Jie Han, Ph.D., PE, F.ASCE Glenn L. Parker Professor of Geotechnical Engineering The University of Kansas, USA Outline of Presentation Introduction Problem Statement Construction of Test Wall Instrumentation Lateral Load Testing and Results Numerical Analysis p-y Curves of Laterally Loaded Piles Cyclic Loading Effect Conclusions Mechanically Stabilized Earth (MSE) Wall - Key Components Drainage Internal and External Stability Analysis of MSE Wall z q r z Facing Reinforced fill Retained fill H W P a(ext) Foundation soil p a(int) =K a(int) H p a(ext) =K a(ext) H 3 4 MSE Wall-Supported Bridge Abutment MSE Wall-Supported Sound Barrier Walls Wind load Sound barrier wall Wind load Highway Casing Bedrock Rock socket Lateral load: traffic loading, thermal effect, earthquake 5 1

2 Basic Design Questions 1. How to design laterally loaded piles behind an MSE wall? 2. How to design an MSE wall considering lateral loads from piles? Current Practice Pile Geosynthetics 3. How to consider cyclic loading effect? Answer: no design method available for these conditions! 7 Leveling pad Rock socket Casing Bedrock Long, large diameter piles, i.e., more costly 8 Proposed Design Research Methodology Leveling pad Again, no design method! Pile Bedrock Geosynthetics More research needed! 9 Theoretical derivation Numerical analysis Laboratory model test Field test KDOT research project investigated Pile offset distance effect Pile length effect Group pile effect 10 Site Location for Field Test Wall 20ft (6m) high 3ft (1m) embedment Test Wall Cross-section 8in (0.2m) impermeable 1 ft (0.3m) drainage fill soil cover Reaction pile Granular backfill Test pile 14ft (4.2m) long Sandstone Limestone Shale Limestone Maintained displacement method for loading tests Google Maps (2008) (KDOT, 2007) 12 2

3 Pile Layout and Plan View Leveling Pad and Metal Pipes for Piles A B Test piles BG BS C D 15ft (4.5m) Reaction piles Used for p-y curve calibration (Tensar, 2007) N Distance to back of wall facing Pile A 3ft (0.9m) 1d 6ft (1.8m) 2d Diameter of test pile (d) = 3ft (0.9m) Pile C 9ft (2.7m) 3d Pile D 12ft (3.6m) 4d 13 Wall Construction Backfill and Compaction Small Compactor Blocks Placement, Leveling Backfill Placement, Leveling, Compaction Geogrid Placement, Trimming (if necessary), Connectors, Pre-tensioning Notes Top Soil Cover Slip Joints Leveling Placement Large Compactor Geogrid must be trimmed to go around the piles Geogrid Connection Tensar Uniaxial Geogrid Spacing: One course every 0.6m or 3 blocks Tensioning of Grid and Placement of CA-5 3

4 Instrumentation Inclinometer Casing Inclinometer Casing Strain Gages on Geogrid Photo Targets Attached to Facing Earth Pressure Cells Behind Facing 19 Strain Gages on Geogrid Photogrammetry Earth Pressure Cell Black area = 0.15m scale 4

5 Single Pile Test Group Pile Test Test Piles 26 Surface Observations Group Test Surface Cracks 4.2m from back of wall Observations Aesthetic Group after test at noon Crack at Back of Reinforced Zone Group after test Group after test afternoon 5

6 Numerical Modeling of Single Pile Numerical Modeling of Group Piles Horizontal deflection Vertical deflection 26ft (8m) 15ft (4.5m) Piles 15ft (4.5m) Numerical Modeling Pre-test modeling Elastic-plastic (M-C) model Typical fill parameters Immediate post-test modeling Elastic-plastic (M-C) model Measured fill parameters Refined modeling Cap-yield model stress dependent Individual blocks Compaction stresses Measured fill parameters 33 (87psi) Stress-strain Curve of Backfill - Refined Model vs. Test Friction angle = 50 o 34 Load vs. Displacement of Single Pile - Test 2 in 4 in 6 in 8 in 10 in kips Pile A Pile C Pile D S % length reduction 40% capacity reduction Serviceability and Ultimate Capacity Load (kn) Serviceability Ultimate Pile offset distance (d) Serviceability = 25 mm (1 in.), Ultimate displacement = 20%d 36 6

7 Load vs. Displacement of Group Piles - Test 2 in 4 in 6 in 8 in 15% reduction kips 200 Vertical Wall Facing Deflection - Model vs. Test 1in 2in 3in 4in Refined 20ft ft Q ult(g) = 85%Q ult(s) Pile group efficiency = 85% Lateral Deflection of Single Pile - Model vs. Test 2in 4in Horizontal Wall Facing Deflection - Single Pile Test at El. 5.4m -10 ft 10 ft 20ft Pile head deflection (mm) 4in 10ft 2in ft Horizontal Wall Facing Deflection - Single Pile Test Pile C at El. 5.6m 10 ft Pile head deflection (mm) 6in Horizontal Wall Facing Deflection Model vs. Test 4in 2in

8 Pile Influence Range 5ft 10ft Lateral Earth Pressure Increase - Model vs. Test Example (): b = d + 2xtan = 17.3ft (5.3m) s = 15ft (4.5m), pile group efficiency = 15/17.3 = 87%, test pile group efficiency = 85% Pile spacing (m) Distance, x Influence range, b 20ft 10ft Refined = o fill friction angle ( ) Lateral Earth Pressure Coefficient Model 20ft Strains in Geogrid Model vs. Test Pile group 10ft Refined K p = Distance from edge of center pile (m) 46 Maximum Tension Increase in Geogrid Model p-y Curve Method for Laterally Loaded Pile Spring stiffness, k (subgrade modulus) p = k y k 1 Refined 47 Sand: Reese s method 48 8

9 Passive Wedge-type Failure of Pile in Sand (Reese et al., 1974) Key Parameters in Reese s Method s This method is included in LPILE software. Back-calculated using tests of piles with level ground Calibration of k Coefficient for p-y Curve Piles in Level Ground vs. behind Wall R3 & R4 = reaction piles in level ground p = k y p = f p = f k y f = p multiplier Back-calculation of p Multiplier p = f p p Multiplier for Resistance Reduction p = f p Lateral load = 227 kn (51 kips)

10 Physical Test Wall in Lab Single Pile Physical Test Wall in Lab Group Piles 56 Static to Cyclic Lateral Load Test Cyclic Lateral Load Test Load (N) Ultimate lateral load capacity D 4d pile offset % d F.S = 2 Single pile 57 Stage of cyclic loading Pile head deflection during cyclic loading Single pile with 2d offset Stage of cyclic loading Pile head deflection during cyclic loading Group piles with 2d offset % increase Static loading 600 Post cyclic loading Load (N) Load-Deflection of Pile Head Pile offset = 2d Load (N) % reduction 19% reduction Single pile Middle pile in group 59 Summary Piles in the MSE wall can carry reasonable lateral loads without socketed into bedrock. Piles had rigid rotation while wall facing had flexible deflections. The MSE wall can tolerate a large local deformation (up to 4 inches or 100mm). Modular blocks can hide the local deformation well. Lateral pile capacity in the MSE wall depends on the distance to the wall facing. Pile group effect depends on pile spacing and the distance to wall facing

11 Summary Acknowledgements Numerical method can reasonably simulate the laterally loaded pile in the MSE wall, especially after considering strain hardening, confining and compaction effect, and discrete blocks. Response of laterally loaded piles can be modeled by p-y curves with p-multipliers (<1.0), which depend on the distance to the wall facing and the lateral load. Cyclic loading increases single pile load capacity, but reduces group pile load capacity. 61 Drs. R.L. Parsons, M. Pierson, and J. Huang Kansas Department of Transportation Applied Foundation Testing Dan Brown and Associates Tensar International Corporation Ph.D. candidate: Saif Jawad Questions? 11