First Use Of Geosynthetic Reinforced Soil – Integrated Bridge System in Illinois

First Use OfGeosynthetic Reinforced Soil –

Integrated Bridge Systemin Illinois

Keith Sargent, P.E.Associate

Thomas Engineering Group

Dr. Riyad Wahab, P.E.State Geotechnical Engineer

IL Dept. of Transportation

What is GRS-IBS?• Alternating layers of compacted granular fill

material and sheets of geotextile reinforcement.

• Face of GRS-IBS wall is CMU or modular blocks.

• Wall is constructed on top of a “Reinforced Soil Foundation” (RSF).

• FHWA promotes the use of GRS-IBS through their “Every Day Counts” and “Accelerated Bridge Construction” programs.

Typical GRS Section

Construction Sequence: Step One

• Lay a row of facing blocks.

Construction Sequence: Step Two

• Add a layer of compacted fill.

Construction Sequence: Step Three

• Add a layer of geosynthetic fabric

What are the benefits?• GRS uses common, readily available materials and

equipment.

• Cost can be up to 25 to 60 percent less than bridges built with traditional methods.

• Easy to maintain due to fewer construction items.

• Reduces construction time.

• Eliminates deep foundations and approach slabs.

Approximate GRS-IBS Costs

• FHWA estimates GRS-IBS using CMU facing to be approximately $33/SF.

• If a wet-cast modular block is used, the estimated cost increase is approximately $28/SF ($61/SF).

• Costs for approach slabs and deep foundations eliminated.

• Comparison: MSE wall costs approximately $55/SF.

GRS-IBS Use in IllinoisFHWA contacted IDOT to search for projects, and in turn IDOT contacted Districts and Local agencies looking for suitable projects:

• Competent soils resistant to scour

• Waterways with 100-yr velocities of 3 ft/sec max

• Non-staged construction

• Low Average Daily Traffic volumes

• Single Span superstructure - range (25 ft - 80 ft)

• Skew 15° or less

• Abutment wall heights not exceeding 30 ft

GRS-IBS Use in Illinois

• The Village of Lombard showed interest in using the GRS-IBS technology for their Great Western Trail project.

• Original plan was to use MSE wall retaining pile supported abutments

• Bollinger, Lach and Associates worked with FHWA and the Village to incorporate GRS-IBS technology into Contract Drawings.

Project Location

MSE Configuration to be Replaced

• 48” deep precast prestressed concrete I beams spanning 92’-6”.•Integral abutments supported by 8 H-piles 80’ long.• 30 ft approach pavement spanning to 10’ wide spread footing.• MSE retaining walls used to shorten span and retain embankment.• Although bridge is for pedestrian use, it is designed for H-20 loading

MSE Configuration to be Replaced

GRS-IBS Design• FHWA has assembled guidelines for design of

GRS-IBS.

• Guidelines provide example plan sheets and details along with approximate quantities.

• Detailed construction specifications are also provided within the guidelines.

• Guidelines account for “favorable” and “poor” soil conditions.

Normal Use is with Concrete Deck Beams

Revised Elevation with GRS-IBS

• Increased Span Length by 6 ft to accommodate blocks and footing.• Deleted 30 ft by 15 in. thick approach pavement and 10 ft footings.• Deleted piles, added 6 ft wide spread footings.• Kept Aggregate column ground improvement.

.

Revised Section with GRS-IBS

• C.I.P. Footing.

• Reinforced Soil Foundation (RSF) on Aggregate Columns.

• Used Extra GRS Aggregate Backfill to transition approach settlement.

• Approach is 3” HMA.

Current Construction Status

• Project was on September 23, 2011 Letting.

• Aggregate Column Ground Improvements - completed on May 29th, 2012.

• Reinforced Soil Foundation and Modular Block Walls (both east and west sides) - completed on August 17th.

• C.I.P. footings - installed August 25th.

• PPC I-Beams to be erected in October.

• Instrumentation to monitor wall movement installed at the end of August (paid for by FHWA).

Aggregate Column Installation

Aggregate Column Installation

Aggregate Column Installation• Installation of Aggregate Columns went

smoothly. • Approximately two days of work for each

abutment.• Approximately 65 columns per abutment.• Test column provided excellent results.

– Loaded to 150% of design load (48 kips)– Deflected less than a ½”

• Total Cost: $108,000

RSF Shop Drawings

RSF Installation

• Four Step Process:– Install geotextile fabric on subgrade leaving excess on

the sides.– Compact lifts of CA-06 stone.– Install layers of geogrid reinforcement.

– Wrap foundation with geotextile fabric.

• Installation of RSF is simple, however this project required foundation steps that complicated the construction.

RSF Construction

Block Shop Drawings

RECON Blocks Selected

• 16”tall, 48”wide 24”deep

• Other approved blocks included Redi Rock and Stone Strong

• Wet Cast Block Required

• To be stained and anti-graffiti surface applied

Modular Block Installation

• Block installation took longer than anticipated given the size of the block (4FT wide x 16” tall x 24” deep).

• FHWA intent is to use 45 LB CMU blocks, not 1600 LB wet cast blocks.

• Approximately 400 blocks per wall.• Making certain blocks are level and set into place

is very important.• Block constructed with no batter, so precision was

crucial.

Modular Block InstallationSetting first row level and in line was very important.

Modular Block InstallationExcavator needed to set block – very time

consuming and difficult to perform precisely.

Geosynthetic Reinforced Soil Installation

• Soil reinforcement was Tenax TT L Type 70 geogrid.– Delivered in 4 FT wide rolls.

– Difficult to cut and lay flat.– Stretching tight was important.

• Select Fill was CA-16.– Required little compaction

– Easy to work with.

Geosynthetic Reinforced Soil Installation

Tenax installed between blocks and halfway up block.

Geosynthetic Reinforced Soil Installation

Final Product

FHWA Monitoring Research• FHWA hired TEG to perform survey monitoring at

regular intervals over the next two years• Goal is to monitor horizontal and vertical displacement of

the wall.

Remaining Work

• Installation of PPC I-Beams

• Superstructure with Safety Railing

• Decorative lighting

• Staining/Coloring of Wall

• Anti-Graffiti Coating with UV Protection

Final Thoughts• The use of GRS-IBS for the Great Western

Trail project in Lombard may not be representative of a usual GRS-IBS project.

• Modular block used for Great Western Trail was large and required heavy machinery and added labor to set in place.

• Modular block used was much more expensive than a standard CMU.

• Overall cost was higher than MSE wall.

Questions?

Email: keiths@thomas-engineering.com

http://www.fhwa.dot.gov/everydaycounts/technology/grs_ibs/