Rev. 7-1-95
GEOGRID FOR SUBGRADE STABILIZATION OR MODIFICATION
617-R-188b
The Standard Specifications are revised as follows:
MATERIALS
617.02 Materials. Materials shall be in accordance with 913.21.
CONSTRUCTION REQUIREMENTS
617.03 Foundation Preparation. The foundation shall be cleared and grubbed in accordance with 201 and excavated using lightweight equipment to minimize disturbance of the foundation soils. Construction activities using heavy weight equipment which cause pumping and rutting of the foundation soils shall be prevented where possible or otherwise minimized. Fine grading may be waived where impractical. However, when very soft soil is encountered, the foundation shall be cleared of all trash and rubbish materials, leaving the roots in place and not disturbing the vegetation cover. The foundation surface shall be subject to inspection and approval prior to geogrid and fill placement. Proofrolling inspection will not be required. 617.04 Geogrid Placement. The geogrid shall be installed in accordance with the manufacturer's recommendations. Excess geogrid shall be removed. As an alternative, the Contractor will be permitted to turn the excess portion of the geogrid into the fill layer as an envelope, provided an acceptable installation is obtained. The geogrid shall be placed taut prior to backfill placement. Installation may require the use of stakes to hold the geogrid in place. The geogrid material supplier shall provide a qualified and experienced manufacturer's representative on the project site at the start of the work to assist the Contractor and the Engineer at the start of construction. The representative shall also be available during construction when required by the Engineer. Geogrid rolls shall be overlapped a minimum of 0.6 m (2.0 ft) side to side and end to end. The geogrids shall be overlapped 0.9 m (3.0 ft) in areas where foundation conditions cannot support workers' foot traffic or where 0.6 m (2.0 ft) is found to be inadequate during fill placement. Overlaps shall be oriented, or shingled, to prevent advancing fill from lifting the geogrid. Overlaps shall be further secured, if necessary, to prevent separation during fill placement, with metal or plastic ties, hog rings, or small mounds of fill. If damage is caused by construction traffic after laying the geogrid, such geogrid shall be patched. Patching shall include placement of a minimum of 0.9 m (3.0 ft) of overlapped geogrid beyond the damaged area. If the damaged portion extends for more than 50 percent of the roll in the width direction, the entire width shall be replaced.
Geogrid shall be covered with fill as soon as reasonably possible after placement. Exposure of geogrid between laydown and cover shall be a maximum of 3 calendar days. Only that amount of geogrid required for immediately pending work shall be placed to prevent damage to the geogrid. Each geogrid roll shall be labeled or tagged to provide product identification sufficient for inventory and quality control purposes. No changes to the geogrid layer, including, but not limited to, length, geogrid type, or elevation shall be made without written consent of the Engineer. 617.05 Fill Placement. Vehicles shall not be permitted on the geogrid before at least 200 mm (8 in.) of fill has been placed on the geogrid. The fill placement shall proceed forward along the roadway centerline and outward to the roadway shoulders of the embankment edges, to minimize wrinkles in the geogrids. The first lift of fill shall be 200 mm (8 in.) loose in thickness to stabilize and eliminate observable displacement of the subgrade under construction vehicular traffic loads. If it is not possible to compact the first lift of fill to 95 percent of maximum dry density in accordance with AASHTO T99, the stabilized fill shall be lightly compacted, so as to prevent excessive loading and destabilization of the subgrade. Subsequent lifts shall be placed and compacted in accordance with 203.23. Heavy compaction equipment and vibratory compactors shall be avoided on the stabilized fill. Fill placed over very soft foundation soil conditions shall require lightweight earth moving equipment. 617.06 Method of Measurement. Geogrid for subgrade stabilization or modification will be measured by the square meter (square yard). The quantity will be computed based on the total area of geogrid shown on the plans, exclusive of the area of geogrids used in overlaps. The portion of geogrid cut off or turned up into the backfill layer will not be measured for payment. 617.07 Basis of Payment. The accepted quantities of geogrid for subgrade stabilization or modification work will be paid for at the contract unit price per square meter (square yard) for geogrid. Payment will be made under:
Pay Item ______________Metric Pay Unit Symbol (English Pay Unit Symbol)
Geogrid, Subgrade ..................................................................m2 (SYS)
The costs of furnishing the materials, manufacturer's representative, all labor, equipment required for furnishing and placing the geogrid, all work necessary to establish grades, geogrid splices, overlaps, stakes or pins, supplemental product test data, and patching or replacement of damaged geogrid shall be included in the cost of this work. SECTION 913, AFTER LINE 5217, INSERT AS FOLLOWS:
913.21 Geogrid. Geogrid shall be a regular network of integrally connected polymer tensile elements with aperture geometry sufficient to permit significant mechanical interlock with the surrounding material. The geogrid structure shall be dimensionally stable and shall be able to retain its geometry under construction stresses. The geogrid structure shall have resistance to damage during construction, ultraviolet degradation, and all forms of chemical and biological degradation encountered in the soil being stabilized. The geogrid shall be in accordance with the property requirements as specified in the Geosynthetic Research Institute Standard Test Methods GG1. (a) Certifications. The Contractor shall submit a type A certification in accordance with 916.02(a). Such certification shall show that the geogrid supplied is in accordance with the respective criteria for all test methods and standards specified. When requested by the Engineer, the Contractor shall supply supplemental product test data from a Department approved independent laboratory to support the certified values submitted. (b) Delivery, Storage, and Handling. The Contractor shall be responsible for the proper delivery of the material. During all periods of shipment and storage, the geogrid shall be protected from temperatures greater than 60EC (140EF), mud, dirt, dust, and debris. The manufacturer's recommendations shall be followed with regard to protection from direct sunlight. At the time of installation, the geogrid will be rejected if it has defects, tears, punctures, flaws, deterioration, or damage incurred during manufacture, transportation, or storage. All damaged portions of geogrid for the entire width shall be replaced. (c) Property Requirements. The geogrid shall be in accordance with the property requirements as follows:
PROPERTY | TEST METHOD | UNIT | VALUE, Min. |
Aperture Size | Calibered | mm (in.) |
19 x 19 (0.75 x 0.75) |
Open Area | COE CWO2215 | percent | >50, <80 |
Tensile Modulus, machine direction or cross machine direction |
GRI, GG11, 3 | N/m (lb/ft) |
146,000 (10,000) |
Ultimate Strength, machine direction or cross machine direction |
GRI GG12,3 | N/m (lb/ft) |
11,670 (800) |
1. Secant modulus at 5 percent elongation measured by Geosynthetic Research Institute Test Method GG1, Geogrid Tensile Strength. No offset allowance shall be made in calculating secant modulus.
2. Ultimate strength measured by Geosynthetic Research Institute Test Method GG1, Geogrid Tensile Strength.
3. Minimum average roll values shall be in accordance with ASTM D 4759.
The geogrids to be used shall be selected from the Department's List of Approved Geogrids for Subgrade Stabilization or Modification.
Requests for adding geogrids to the approved list shall be supported by means of a certification which documents compliance with the above requirements and a 1 running meter (1 running yd) sample. The certification shall be prepared by the manufacturer in accordance with the applicable requirements of 916. No relabeled materials will be considered for approval. A specified material shown on the approved list will not be listed under more than one name. When it is determined that the material is acceptable, it will be added to the List of Approved Geogrids for Subgrade Stabilization or Modification, which will be maintained by the Division of Materials and Tests.