1. Overview of Integrated Bridge Systems - Geosynthetic Reinforced Soil (IBS-GRS) Abutments
Emad Ghodrati1, Evert Lawton2
1 Graduate Student, Dept. Civil & Environmental Eng., University of Utah
2 Professor, Dept. Civil & Environmental Eng., University of Utah
Workshop on Emerging Bridge Support and Embankment Technologies
Salt Lake City, UT, October12, 2016

2. Outline Definition and benefits Definition
Benefit compare to conventional bridge abutments
Recent design guidelines
NCHRP 556 (2006) background research and recommended procedure
FHWA GRS-IBS interim implementation Guide (2012)
Few example of the current research to improve the design procedure
Analytical solution for settlement (Hoffman & Wu)
Deformation of GRS performance test (Nicks et al.)
Optimum reinforcement density(Xie&Leshchinsky)
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

3. GRS-IBS definition: Geosynthetic Reinforced Soil (GRS)
Alternating layers of compacted granular soil reinforced with closely spaced geosynthetic material (less than 12 in. according to FHWA).
Integrated Bridge System (IBS)
A cost-effective method to support the bridge superstructure on the GRS fill and integrate the roadway into the superstructure
Definition by FHWA
Ref: Fig1: Geosynthetic Reinforced Soil Integrated Bridge System Synthesis Report
Ref. Fig2: MONITORED DISPLACEMENTS OF UNIQUE GEOSYNTHETIC-REINFORCED SOIL BRIDGE ABUTMENTS, 2002, by N. Abu-Hejleh, J.G. Zornberg, T. Wang, and J. Watcharamonthein
Founders/Meadows structure near Denver, Colorado,

4. Definition by FHWA
Ref: Fig1: Geosynthetic Reinforced Soil Integrated Bridge System Synthesis Report
Ref. Fig2: MONITORED DISPLACEMENTS OF UNIQUE GEOSYNTHETIC-REINFORCED SOIL BRIDGE ABUTMENTS, 2002, by N. Abu-Hejleh, J.G. Zornberg, T. Wang, and J. Watcharamonthein
Founders/Meadows structure near Denver, Colorado,

5. Founders/Meadows structure near Denver, Colorado,

6. GRS-IBS benefits:
Lower construction and maintenance cost compare to conventional system (i.e., sloped embankment, reinforced concrete cantilever retaining wall, and etc.)
Faster construction
No need for special equipment and specialized construction crew
Smother transition from approach slab to the bridge deck (reduced bump at the end of the bridge)
Not much embedment is needed
More flexible and less sensitive to differential settlement compare to conventional options
Better performance in extreme loading condition such as Earthquake and Tsunami compare to conventional system (Japan)
2H:1V negative batter on a wall 30 feet high (Japan)
Cost:
25–30 percent lower cost than standard pile cap abutments on deep foundations with 2:1 slopes for off-system bridges.
50–60 percent lower cost than standard department of transportation bridges.
Embedment:
environmental problem such as excavation into previous contaminated soil is involved.
Ref Fig1: Barrett, R.K., and Ruckman, A.C., “GRS−A New Era in Reinforced Soil Technology.” Proceedings, GeoDenver 2007, Geosynthetics in Reinforcement and Hydraulic Applications, ASCE, 2007.
Bowman Road Bridge (Ohio) after 4.5 years

7. NCHRP full scale test abutment
Two different (21 kN/m and 70 kN/m tensile strength) 3.5m long reinforcement at each face with 0.2m spacing.
Concrete “cinder” block with frictional connection
4.65m high
SP-SM backfill with 8.5% fine. 100% target compaction of standard proctor compaction
34.8 friction angle and 13.8 kPa cohesion intercept using direct shear test on particle finer than No.10 sieve
Large scale triaxial test: 37.3 friction angle and 20kPa cohesion intercept

9. Tult = 70 kN/m
Tult = 21 kN/m
Average settlement at the seat “sill”

10. Lateral displacement
for GRS abutment with
Tult = 70 kN/m
Lateral displacement
for GRS abutment with
Tult = 21 kN/m

12. Numerical parametric study by Helwany and Wu
Increase in reinforcement spacing increase the displacement
Increase in backfill friction angle (relative compaction) decrease the displacement
Increase in reinforcement stiffness decrease the displacement
Dyna3D model
Von-mises model for reinforcement
Drucker-prager with cap for soil (isotropic)
1% of H settlement to choose the appropriate pressure of the sill (2% long term with creep)
S = 20cm
S = 20cm
Reinforcement spacing (cm)
Friction angle
Reinforcement stiffness (kN/m)

13. NCHRP report 556 Design procedure
Ultimate capacity: Determine the maximum ultimate pressure on the abutment using the given table and modify by the graph. Multiply the strength by 0.75 for isolated sill and by 1 for integrated sill
Settlement: 1.5% of H
Check pull out
Evaluate stability of the footing
Check the global stability
For reinforcement: The recommended combined safety factor is Fs = 5.5 for reinforcement spacing ≤ 0.2 m, and Fs = 3.5 for reinforcement spacing of 0.4 m.
1% of H settlement to choose the appropriate pressure of the sill (2% long term with creep)

14. NCHRP report 556 Design procedure
Limitation
Hmax = 10m
Dry-stacked concrete modular block
At least 34º friction angle for material passing No.10 sieve compacted to 95% of standard compaction test
100 percent passing 10 cm (4 in.) sieve, 0 to 60 percent passing mm (No. 40) sieve, and 0 to 15 percent passing mm (No. 200) sieve, free from organic material, plasticity index not greater than 6.
At least 100% relative compaction (standard compaction) of the fill material
Competent foundation (at least Su = 140kPa for clay and 20 SPT blow count for granular soil)
Minimum 0.3m clearance from the back of the facing and the sill

15. NCHRP report 556 Design procedure
Tolerable settlement of 100mm(4in.) and lateral displacement of 50mm(2in.)
Well-graded and well-compacted granular material with closely spaced (0.2m) may provide up to 900kPa load-carrying capacity.
Preloading can reduce the post-construction settlement 2 to 6 times.
The default spacing of reinforcement is set to 0.2m and spacing more than 0.4m is not recommended.
For competent foundation reinforcement length of 0.35H with 45 degree increase in length by height. Use reinforced soil foundation for poor foundation.

16. FHWA Interim Implementation Guide
Minimum requirement
Hmax = 10m
At least 38º friction angle for backfill material
Minimum compaction of 95% of standard compaction test
Maximum 12% fine
Reinforcement with at least 70 kN/m ultimate tensile strength
Maximum bearing of about 190 kPa
Maximum span of about 43m
Maximum 0.5% vertical strain and 1% lateral strain
Maximum reinforcement spacing of 0.3m in GRS abutment and 0.15m at the bearing bed
External Stability (overturning is not possible)
Facing is not a structural member
Creep is considered in the factor of safety
For span lengths (Lspan) greater than or equal to 25 ft, a minimum base width of the wall including the block face (Btotal) of 6 ft should initially be chosen. For span lengths (Lspan) less than 25 ft, a minimum base width of the wall including the block face (Btotal) of 5 ft should initially be chosen. At least 0.3H

17. NCHRP report 556 Backfill Requirement

18. External stability (Sliding, Bearing capacity and global stability)
Design Procedure
Ultimate capacity: Determine the ultimate vertical capacity on the abutment either a performance test or using W-equation
Settlement: For material similar to the given test result, the given curve may be used otherwise a performance test is needed
Lateral deformation: by assuming zero volume change, it is twice the vertical strain
External stability (Sliding, Bearing capacity and global stability)
Facing is not a structural member
Creep is considered in the factor of safety
For span lengths (Lspan) greater than or equal to 25 ft, a minimum base width of the wall including the block face (Btotal) of 6 ft should initially be chosen. For span lengths (Lspan) less than 25 ft, a minimum base width of the wall including the block face (Btotal) of 5 ft should initially be chosen. At least 0.3H

19. The W-Equation has a good correlation with measured data
Facing is not a structural member
Creep is considered in the factor of safety
For span lengths (Lspan) greater than or equal to 25 ft, a minimum base width of the wall including the block face (Btotal) of 6 ft should initially be chosen. For span lengths (Lspan) less than 25 ft, a minimum base width of the wall including the block face (Btotal) of 5 ft should initially be chosen. At least 0.3H

20. Analytical solution for settlement (Hoffman&Wu)

21. Step 1

22. The interpretation of the second observation is that sH/sV decreases from KA to a value MKA where stresses in the soil are again in equilibrium with those in the reinforcement. M is the fraction of reinforcement strength that can be mobilized for load-carrying, and the remainin fraction 12Mconverts failure into orderly plastic deformation.
Step 2: Calculate the reinforcement mobilization factor by solving 3 nonlinear equation

23. Step 3:

24. Step 4:

25. Cons:
Complicated
Requires good estimate for friction angle considering the curved nature of the graph (for prediction more precise is needed)
Need assumption of compaction induced stress

26. Deformation of GRS performance test(Nicks et al.)
They performed 13 Performance Test (PT) with different backfill, facing, reinforcement spacing and strength

27. Deformation of GRS performance test(Nicks et al.)
Findings:
The smaller size OGA result in less settlement due to higher contact point and less void
Facing blocks can reduce the settlement 50% to 75%
The reinforcement spacing has more influence than its strength
The maximum lateral displacement happens in the top third height
The theoretical investigation by Adams et al. showed that the stiffness of GRS abutment is about 0.92 to 3 times the stiffness of PT
Suggested allowable vertical pressure to limit vertical strain to 0.5%
The allowable applied pressure at 0.5% vertical strain (target limit)
ranges between about 7 percent and 13 percent of the ultimate
bearing resistance, with an average of 10 percent

28. Optimum reinforcement density(Xie&Leshchinsky)
Limit Analysis (LA) and a Discontinuity Layout Optimization (DLO)
MSE walls as bridge abutments: Optimal reinforcement density 2015
The reinforcements connection to the modular block facing was modeled as a perfect mechanical connection (no frictional interaction). Also, the surcharge footing was modeled as a weightless rigid block.

29. Increasing the reinforcement strength, increases the bearing capacity
Increase in the densely reinforced portion of the abutment from top to bottom resulted in increase in the overall bearing capacity of the GRS abutment up to a point.
Increasing the setback of the surcharge load increases the overall bearing capacity of the system.
Increasing the reinforcement strength, increases the bearing capacity
increase in the densely reinforced portion of the abutment from top to bottom resulted in increase in the overall earing capacity of the GRS abutment up to a point.
the bearing capacity reaches an asymptote, because the general bearing capacity failure under the surcharge footing controlled the overall failure of the system.
the setback of the surcharge load from the tip of the wall increased the overall bearing capacity of the system

30. increase in the densely reinforced portion of the abutment from top to bottom resulted in increase in the overall earing capacity of the GRS abutment up to a point.
the bearing capacity reaches an asymptote, because the general bearing capacity failure under the surcharge footing controlled the overall failure of the system.
the setback of the surcharge load from the tip of the wall increased the overall bearing capacity of the system

31. Reference
Abu-Hejleh N., Zornberg, J.G., Wang, T., and Watcharamonthein, J. (2002) “Monitored Displacements of Unique Geosynthetic-Reinforced Soil Bridge Abutment”, Geosynthetics International, 9(1), pp
Wu, J.T.H., Lee, K.Z.Z., Helwany, S.B., and Ketchart, K. (2006) “Design and Construction Guidelines for GRS Bridge Abutment with a Flexible Facing, Report No. 556”, National Cooperative Highway Research Program (NCHRP), Washington, DC.
Adams, M.T., Nicks, J.E., Stabile, T., Wu, J.T.H., Schlatter, and W., Hartmann, J. (2011) “Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide. Final Report”, FHWA-HRT Federal Highway Administration, McLean, VA.
Hoffman, P., and Wu, J.T. H. (2015)“An analytical model for predicting load–deformation behavior of the FHWA GRS-IBS performance test”, International Journal of Geotechnical Engineering, 9(2), pp
Nicks, J.E., Esmaili, D., and Adams, M.T. (2016) “Deformations of geosynthetic reinforced soil under bridge service loads”, Geotextiles and Geomembranes, 44, pp
Xie, Y., Leshchinsky, B.(2015) “MSE walls as bridge abutments: Optimal reinforcement density”, Geotextiles and Geomembranes e138

32. Thank you for your attention!