Geogrids. Geogrids. Biaxial Geogrids OUR FOCUS TODAY

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1 OUR FOCUS TODAY BX (Biaxial) Geogrids and how they can help you solve site Subgrade Problems for any pavement type OUR FOCUS TODAY Geogrids...improve the performance or Biaxial provide economic benefits - Bi-Directional o f any flexible pavement - Polypropylene - High Low Strains - Pavements & Foundations Geogrids Uniaxial One Directional - HDPE - High Low Strains - Slopes & Retaining Walls Biaxial Geogrids Two Basic Applications Base Reinforcement & Subgrade Improvement 1 2

2 Base Reinforcement Structural Pavement Reinforcement Subgrade Improvement Soft Soil Reinforcement Increased Service Life for Long-Term Economy Alton Heights Subdivision - Alton, KY Geogrids Are NOT Fabrics Different Functions Different Properties Different Specification Criteria Fabric Uses Fabric Used in Pavements They Do Not Reinforce SEPARATION They Separate Subgrade Im provem ent M echanism s Literature Review on Geotextiles - COE...if geotextiles are included in the structure (of a pavement), no structural support should be attributed to geotextiles. geotextiles should be used in filtration, drainage, and separation, but not reinforcement 13

3 Filtration * Drainage AASHTO M288 G en eric G eotextile S pec Erosion Control Silt Fence Separation Geogrids Were Designed to Reinforce W hat is the difference between Fabrics & Geogrids? But Not Reinforcement! DISTINCTIONS Tensile Modulus TENSILE MODULUS A fancy word fo r the relationship between the amount a material will stretch under a given load Strain Compatibility Geogrids have a high Tensile Modulus Compared to Fabrics Strain TENSILE MODULUS What Type o f Reinforcing Would You Use? - Steel Rebar TENSILE MODULUS S u bgrade S o ils are L ike C on crete Weak in Tension - A Bungee Cord o f Equal Strength The High Tensile Modulus Steel - o f Course! Fail with very little Stretching -Therefore- Reinforcement Must have a High Modulus 14

4 Field Proof DISTINCTIONS Apertures TENSAR Geogrid Fabric N ote how the Fabric Ruts Mechanical Interlock Confinement DISTINCTIONS Flexural Rigidity Structural Capabilities These properties allow biaxial geogrids to provide Structural Value Less Stone and Less Cost -vs.- Fabrics and Chemical Treatments Stiffness helps protect existing subgrade strength BX Geogrid Reinforcem ent Capabilities 1984 University o f W aterloo - Test Results LDOP1 Even works where you think it s not needed Le. go o d subgrades Proven by Research an d... In-ground Performance Extended Service Life (Higher SN Value) 15

5 1984 University o f W aterloo - Test Results LOOP2 Traffic Benefit Ratio (TBR) Ratio o f the number o f loads to failure with Geogrid vs. without Geogrid Reduced Aggregate Thickness - Maintains Same Service Life 1984 University of W aterloo The Bottom Line Traffic Benefit Ratio (TBR) = 3.0 or an increase to 300% o f original service life Up to 50% Reduction in Base Course Thickness Summary of Research University of Waterloo BX1100 TBR = 3 Corps of Engineers BX1100 TBR = 2.7 BX1200 TBR = 4.7 University of Alaska B X1100 TBR = 2-3 BX1200 TBR = 2-10 Montana State University Verifies a M inimum BX1100 TBR = 3 TBR Varies Some with Base Thickness 1992 US Army Corps of Engineers USDOT/FAA commissioned study for reinforcing airfield pavements Phase I - Geotextile 1992 US Army Corps o f Engineers Phase I - Geotextile Literature Review states th at.....geogrids have more potential than geotextiles for reinforcement o f flexible pavements." Also "...if geotextiles are included in the structure, no structural support should be attributed to geotextiles. 16

6 1992 US Army Corps o f Engineers Phase II - Geogrid Literature Review Geogrids perform better than geotextiles in base layer reinforcement m ainly because o f grid interlock with aggregate particles. Poor friction properties o f geotextiles do not allow good interlock with aggregate particles US Army Corps o f Engineers Phase III - Geogrid Reinforcing Full Scale Test Full Scale Test Report on all commercially available geogrids - Therefore- Full Scale Testing o f Geogrids was Recommended 1992 US Army Corps o f Engineers Several Grids Tested COE Results N ot A ll Geogrids Perform The Same W hy the Difference in Perform ance??? Common M aterial Properties Tensile Strength and M odulus Aperture Size Junction Strength Stiffness Soil Particle Movement Direction of Wheel Path Pattern COE E nlist the Help o f Dr. Kinney 17

7 H ow Properly D esigned G eogrids Work CONFINEMENT University of Alaska & COE Torsional Rigidity Modulus A Measure o f the Resistance to: In-plane Rotation Fishhook Particle Movement Aggregate Restraint Correlates to In-Ground Performance In- Ground Performance is Predicted by Torsional Rigidity Torsional Rigidity (cmkg/deg) Traffic Benefit Ratio (TBR) TORSIONAL RIGIDITY Not all Geogrids are Equal" Specifications Sheet Comparisons DO NOT Prove Equivalence Biaxial Geogrids Two Basic Applications Good Subgrades & Poor Subgrade BX Geogrid Applications Base Reinforcement & Subgrade Improvement Combination 1 8

8 Subgrade Improvement Soft Soil Reinforcement Cost Effective Solution TH E PROBLEM! Immediate Results THE SOLUTION! Subgrade Improvem ent M echanisms Are Sim ilar to Base Reinforcement Design Tools Good Subgrades Structural Pavement Reinforcement Reduce Aggregate Thickness for Immediate Economy Increased Service Life for Long-Term Economy 19

9 Base Reinforcement Economic Benefits Design Tools Reduced Initial Construction Cost Quicker Construction Up to 50% Less Aggregate Base Required Less Expensive Pavement Easy to Install Cost Effective No special equipment BX Installation BX Installation One-Step Application No mixing No waiting Immediate Results Readily Available Environmentally Friendly No Dust to drift or breathe STRUCTURAL Geogrids BX Geogrid Applications Proven Performance & Economy in Good Subgrade Conditions Base Reinforcement Proven Performance & Economy in Poor Subgrade Conditions Subgrade Im provement Base Reinforcement & Subgrade Improvement Combination 20

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