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GRS-IBS BridgesDesign Methodology and Construction Techniques for a Successful Bridge

Replacement

2020 Statewide Conference on Local Bridges

• What is GRS-IBS?• When and Why was it developed?• Where is GRS-IBS being used?• What materials are required?• Advantages vs. Disadvantages• Design and construction needs

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Presentation Outline

• Geosynthetically Reinforced Soil – Integrated BridgeSystem

• First used in the 1970’s for retaining wall structures builtby the US Forest Service

• Adapted for use in bridges by Colorado DOT and FHWA inmid-1990’s

• GRS structures differ from MSE (Mechanically StabilizedEarth) structures

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What is GRS-IBS?

• Three Main Components• Reinforced Soil Foundation• Abutment (Facing Element, Backfill, Geotextile Reinforcement)• Integrated Approach

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What is GRS-IBS?

• The first GRS-IBS bridge on record was built in DefianceCounty, Ohio in 2005

• Since it’s construction Defiance County has built 24 moreGRS-IBS bridges.

• More widespread acceptance due to FHWA’s Every DayCounts initiative in 2010

• According to FHWA, approximately 300 structures existacross 44 states as of 2018

• New Yorkà St. Lawrence, Madison, Ulster and ColumbiaCounties

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Where are GRS-IBS Structures Being Used?

• Materials• Facing Blocks/Units• Geosynthetic

Reinforcement• Compacted Backfill

• Equipment• Measuring Devices/Survey

Equipment• Small Excavator• Hand Tools• Walk Behind Compactor

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Materials and Equipment Needed

• Standard 7-5/8” x 7-5/8” x15-5/8 CMU Blocks orSegmental Retaining WallBlocks

• Meets ASTM C1262-10Requirements forFreeze/Thaw

• Non-StructuralComponent

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Materials – CMU Block

• Select Structure Backfill compacted to 95%

• Compact in 4” Lifts

• Open Graded vs. Well Graded Backfill Types

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Materials - Backfill

• Can be Uniaxial or Biaxialà If using uniaxial, make surefabric is installed in proper direction

• Ultimate Tensile Stress of 4,800 psi

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Materials – Geotextile Fabric

• Advantages• Readily Available Materials & Ease of Construction

• Not Limited by Weather Concerns

• More Customizable than MSE Structure

• Cost Effective and Shorter Duration

• Less Susceptible to Movement

• Reduces Differential Settlement at Approach

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Advantages of GRS-IBS Usage

• Simple Span Structures Less Than +/- 140’ Long

• Low Velocity Streams or Location of Flow Equalization

• When Founded Behind Existing Abutments to Remain

• Roads Over Other Roadways

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When To Use GRS-IBS?

• Long Span and Multi-Span Configurations

• Scour Critical Locations

• When Deep Foundations are Required

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When To NOT Use GRS-IBS

• Blockà Fillà GeotextileàREPEAT!

• Ensure First Layer of Block isLevel

• Composite Construction

• Geosynthetic Layers RestrainLateral Deformations

• Additional Geotextile Layersin Bridge Seat

• Jointless Construction andIntegrated Approach

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Design Methodology and Features

• Solid Blocks at the bottom courses, sometimes differentcolors

• Upper courses of block at beam seat are groutedtogether and pinned with rebar

• Design takes into account sliding, bearing resistance ofsoil before RSF and global stability. Eccentric loading andoverturning do not need to be checked

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Design Methodology and Features

• Ensure All Granular Fill is Swept From Top of Block BeforePlacing Next Layer

• Ensure Geotextile is Oriented in Proper Direction

• Avoid Wrinkles in Geotextile

• Avoid Use of Track Mounted Equipment on Geotextile

• Superstructure types can be prestressed concrete beamsor steel girders

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Construction Techniques

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Construction Techniques

• In the fabrication of the CMU blocks, ASTM C1262-10states the requirements that need to be met for whichmaterial property of the block?

A. Load Bearing Capacity

B. Resistance to freeze/thaw conditions

C. Fire Resistance

D. Finished Appearance

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Learning Assessment #1

• In the fabrication of the CMU blocks, ASTM C1262-10states the requirements to that need to be met for whichmaterial property of the block?

A. Load Bearing Capacity

B. Resistance to freeze/thaw conditions

C. Fire Resistance

D. Finished Appearance

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Learning Assessment #1

• Which of the following steps is important in the properinstallation of the geotextile membrane?

A. Place the geotextile membrane in the direction of greatestreinforcement strength parallel to the wall

B. Place the geotextile membrane in the direction of greatestreinforcement strength perpendicular to the wall

C. Installing overlaps between adjacent layers of geotextile

D. Allowing granular fill to exist on top of the CMU block as itcreates additional friction between the geotextile and block

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Learning Assessment #2

• Which of the following steps is important in the properinstallation of the geotextile membrane?

A. Place the geotextile membrane in the direction of greatestreinforcement strength parallel to the wall

B. Place the geotextile membrane in the direction of greatestreinforcement strength perpendicular to the wall

C. Installing overlaps between adjacent layers of geotextile

D. Allowing granular fill to exist on top of the CMU block as itcreates additional friction between the geotextile and block

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Learning Assessment #2

• Which failure method is NOT required to be checked inthe design of a GRS abutment?

A. Overturning

B. Sliding

C. Soil Bearing Resistance

D. Global Stability

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Learning Assessment #3

• Which load failure method is NOT required to be checkedin the design of a GRS abutment?

A. Overturning

B. Sliding

C. Soil Bearing Resistance

D. Global Stability

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Learning Assessment #3

• FHWA-HRT-17-080 – Design and Construction Guidelinesfor Geosynthetic Reinforced Soil Abutments andIntegrated Bridge Systems, June 2018

• NYSDOT GEM-28 – Guidelines for Design andConstruction of Geosynthetic Reinforced Soil IntegratedBridge System, August 2015

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Additional Reference Materials

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Questions??

Byron S. Raych, P.E.Managing Engineer

Barton & Loguidice, D.PC.braych@bartonandloguidice.com