809Geogrid Materials

809.1General Description

This Specification includes requirements for geogrid used in reinforced slopes and Mechanically Stabilized Embankment (MSE) Wall backfill. 809.1.01 Definitions ASTM—American Society for Testing and Materials GRI—Geosynthetic Research Institute 809.1.02 Related References

AASHTO Task Force 27 Guidelines U.S. Environmental Protection Agency, Method 9090—Chemical Compatibility Association of Textile Chemists and Colorists, Method 30—Soil Burial American association of Textile Chemists and Colorists, Method 100—Preparation of Bacterial Broth ASTM D 638 ASTM D 746 ASTM D 975 ASTM D 1238 ASTM D 1505 ASTM D 1525 ASTM D 2165 ASTM D 4355 ASTM D 4595 GRI—GG1 GRI—GG2-87 GRI—GG3a or GG3b GRI—GG5 809.1.03 Submittals Supply certification from the manufacturer showing the physical properties of the material used and conformance with the specifications according to Subsection 106.05 of the specifications. Provide evidence from the manufacturer that the geogrid has been used successfully in installations with similar environmental and project conditions. Obtain prior approval from the Office of Materials and Research for all materials before use on construction. 1467 1467 1467

Submit product specifications and test results to the Engineer for review and approval at least 45 days prior to intended use. Do not begin placement of geogrid until the test results have been reviewed and approved by the Engineer.

809.2Materials

Use geogrid that is free of defects, punctures or flaws.

Use geogrid materials for reinforced slope construction that consist of the following: • Either a biaxial or uniaxial grid of polymer tensile elements manufactured into a regular network with apertures of sufficient size to allow for soil interlock. • A commercially prepared material of high tenacity polyester, high density polyethylene (HDPE) or polypropylene that is formed by stretching, heat welding, chemical welding, knitting, weaving or combinations of these methods. Adhere to the following additional requirements: Long Term Design Strengths 1) Use geogrid that meets the minimum long-term design strengths (TLT) in the machine direction as indicated on the plans. 2) Provide to the Engineer, in writing, the ultimate tensile strength of the grid (TULT) to verify the calculation in obtaining the long-term design loads (TLT). These strengths are required for the Project and are determined based on the AASHTO Task Force 27 guidelines, which incorporates reduction factors to the ultimate strength of the geogrid for creep, site damage and durability. 3) Calculate the long-term design strength using the following formula: TLT = TULT x CRC FC x FD Where: TLT = Long-term design load—lb/ft (kg/m) TULT = Geogrid ultimate tensile strength—lb./ft. (kg/m) CRC = Creep reduction coefficient FC = Factor of safety to account for construction damage FD = Factor of safety to account for product durability

Determine the TULT based on wide strip tensile testing as noted in Subsection 809.2.02.

Determine the reduction factors by the methods described in paragraphs a - e as follows: 1) Creep

tests according to the following criteria: • Conducted for a minimum duration of 10,000 hours • Tests were made for a range of load levels, including loads that the geogrid will be subjected to on the project.

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10% within the design life of 75 years (designated Tw).

CRC = Tw TULT In the absence of test data, use the following creep reduction factors for different polymers: Polymer Type Creep Reduction Coefficient Polyester 0.40 Polypropylene 0.20 Polyamide 0.35 Polyethylene 0.20 2) Construction Damage

construction damage tests using fill materials and construction procedures which are representative of those on the project.

FC = TULT TC Where: FC = The construction damage factor TC = The ultimate strength of the excavated grid that has been subjected to construction damage tests. TULT = Geogrid ultimate tensile strength—lb/ft (kg/m)

than those represented on the Project, use a minimum value of FC of 1.25. Use a lower value of FC only if substantiated with damage tests using fills and construction procedures specific to the project.

3) Product Durability

durability tests to examine the effects of chemical and biological exposure on the grid, as described in the AASHTO Task Force 27 report.

• Effect on short-term and long-term mechanical properties. • Changes to the following: • Reinforcement microstructure • Dimensions • Mass • Oxidation • Environmental stress cracking • Hydrolysis 1469 1469 1469

• Temperature • Plasticization • Surface micrology • Variations in the infrared spectrum analysis. • A full investigation into the synergetic effects of different environments, particularly temperature. Subject the reinforcement to a working stress during the environmental test.

outlined by the following, as a minimum: • U.S. Environmental Protection Agency, Method 9090 – Chemical Compatibility. • Association of Textile Chemists and Colorists, Method 30 – Soil Burial. • American Association of Textile Chemists and Colorists, Method 100 – Preparation of Bacterial Broth.

exposed and shall include as a minimum: • pH in the range of 2, 4, 8, 12 – ASTM-D-2165 • Diesel oil – ASTM-D-975 • Fungi and Bacteria • UV exposure 500 hrs. – ASTM-D-4355 • Solvents and agents that are site specific. In the performance of this testing the conditioning temperature is laboratory standard plus 1.5 times laboratory standard for the pH environments. When no conditioning time period is given, use 30 days. Extrapolate results from short-term tests to the required design life of 75 years. After the geogrid is subjected to these conditions, test the geogrid according to Subsection 809.2.02, and calculate the durability factor of safety by the following formula: FD = TULT TD Where: TD= The ultimate strength of the geogrid subjected to product durability tests. The minimum allowable value of FD is 1.10. In the absence of any geogrid durability tests, use a Durability Factor (FD) of 2.0. 4) Pullout Resistance:

tests using backfill materials representative of those on the Project, as described in the AASHTO Task Force 27 report.

(19 mm) as measured at the leading edge of the compressive zone within the soil mass and not the ultimate pullout capacity.

type, conduct pullout tests on a project specific basis until the engineering behavior of the soil- reinforcement system is clearly defined.

simulating actual project conditions. 1470 1470 1470

length of 2 ft. (600 mm). Perform the tests on samples with a minimum width of 1 ft. (300 mm), or a width equal to a 4 longitudinal grid element, whichever is greater. Conduct the tests at 70 oF ±4 oF (21ºC ± 2 °C) at constant strain rates of 0.02 in. (0.5mm) per minute. Evaluate the pullout resistance by the following relation: Tp = (2 tan P) x Sv x Ls x fd Where: Tp = Ultimate pullout capacity of tensile reinforcement—lb./ft. (kg/m) Sv = Vertical stress—lb./ ft. 2 (kg/m2) Ls = Total length of geogrid beyond failure plane—ft. (m) P = Internal angle of friction of select backfill fd = Equivalent coefficient of direct sliding derived from pullout tests The equivalent coefficient of direct sliding, fd, may be related to the open area of the grid. In the absence of product specific data tested with site-specific granular backfill, estimate the from the following preliminary analysis: % Open Area of Grid Direct Sliding 80% more 0.5 51 to 79 0.7 50 or less 0.6 Ensure the pullout resistance, Tp, meets the following minimum strength requirement: Tp = FPO x TLT with a displacement less than or equal to ¾ in. (19 mm) Where: FPO = Factor of safety against pullout, equal to 1.5 TLT = Long-term design load—lb./ft. (kg/m) 1471 1471 1471

5) Junction Strength:

length of the grid sample is greater than the ultimate tensile strength of the element to which they are attached.

shear strengths to the ultimate strength.

ultimate strength per element by dividing the number of elements per foot (meter) of width.

Use geogrid materials for MSE wall construction that meets the following requirements: • Is a biaxial grid of polymer tensile elements manufactured into a regular network with apertures of sufficient size to allow for soil interlock. • Is a commercially prepared material of copolymerized high density polyethylene (HDPE) that is formed by stretching, heat welding, chemical welding, or combinations of these methods. • Has the following physical properties: Physical Properties Property Requirement Melt Index 0.00176 - 0.00846 oz./10 min. (0.05 -0.24 grams/10 min.) Density 59.0 – 59.6 pcf (0.945 - 0.955 grams/cc) Tensile Strength 500 ksf (24 000 kPa) minimum Ultimate Elongation 500% min. Brittleness -100 o F (-73 o C) maximum Vicat Softening Point 260 oF (127 oC) minimum Chemical Resistance Resistant to all natural occurring alkaline and acidic soil conditions Biological Resistance Resistant to attack by bacteria and fungi

• Has the following structural and mechanical properties:

MSE Wall Geogrid—Structural and Mechanical Properties

Property Requirement

Roll Length 100 ft. (30 m)

Roll Width 3 ft. or 4.5 ft. (1 m or 1.4 m)

Roll Weight 82 lb.—3 ft. roll (37.2 kg—1 m roll); or 114 lb.—4.5 ft. roll (51.7 kg—1.4 m roll)

Grid Pitch 0.6 in. x 4 in. (15 x 100mm)

Color Black

Ultimate Tensile Strength 7.47 kips/ft. (109 kN/m) 147214721472

MSE Wall Geogrid—Structural and Mechanical Properties

Property Requirement

Extension @ Ult. Tensile Strength 17.0% maximum

Extension @ Design Load (0.4 Ult.) 3.0% maximum

Modulus in Tension 9000 ksi (62 000 MPa)

Thermal Stability Stable over a range of -60 o

F to 174 o

F (-51 o

C to 79 o

C)

Note: Tests are based on 10 single rib samples extended at a constant rate of 1 in. (25 mm)/min. at a temperature of

68 ± 4 o

F (20 ± 2 o

C.)

General Provisions 101 through 150.

Test geogrid according to the following:

Test Property Test Method

Reinforced Slopes

Tensile Strength—Wide Width ASTM D 4595

Tensile Strength—Single Rib Strand GRI – GG1

Junction Strength GRI – GG2-87

Tensile Creep Testing GRI – GG3a or GG3b

Geogrid Pullout GRI –GG5

MSE Wall Backfill Stabilizing Geogrid

Melt Index ASTM D 1238

Density ASTM D 1505

Tensile Strength ASTM D 638

Ultimate Elongation ASTM D 638

Vicat Softening Point ASTM D 1525

Brittleness ASTM D 746

General Provisions 101 through 150.

809.2.01 Delivery, Storage, and Handling

During shipment and storage, protect the grid from mud, dirt, dust, debris and exposure to ultraviolet light,

including sunlight.. 1473 1473 1473