Section 207 — Earthwork Geosynthetics

Description

207.01This work consists of providing and installing geotextile in separation, stabilization, filter, and reinforcement applications, geogrid in stabilization and reinforcement applications, and geomembranes in moisture barrier applications.

Material

207.02Conform to the following Subsections: Geomembranes 714.05 Geotextile 714.01 Reinforcement geotextile and geogrid 714.04 Stabilization geogrid 714.03

Construction Requirements

207.03General . Identify, store, and handle geosynthetics according to ASTM D4873 and the manufacturer’s recommendations. Elevate and protect geosynthetic rolls with a waterproof cover if stored outdoors. Maintain product identification label s in a visible location on the inside of the core. Limit geosynthetics exposure to less than 10 days of ultraviolet radiation. Unless otherwise specified, overlap geosynthetic s in the direction, sequence, and distance according to the manufacturer’s recomm endations. For seams sewn on site, comply with the manufacturer’s recommendations. Obtain approval of the seam before installation. Use thread consisting of high strength polypropylene or polyester. Do not use nylon thread. Use thread that is resistant to ultraviolet radiation and a contrasting color to the geotextile. If geosynthetic joints are field constructed , submit an installation plan according to Subsection 104.06 at least 14 days before installation that includes proposed equipment, the QCP, and the follow ing:

(a)Assembly description. Include the seam type, seam allowance, stitch type, sewing thread tex ticket numbers and types, stitch density, and stitch gauge;

(b)Proposed panel layout drawing. Show seam and overlap locations ; and

(c)Sewn seam samples. Sew seam samples using the same equipment and procedures used to sew production seams. Submit samples that have at least 6 feet of sewn seam and are at least 5 feet wide. If production seams are sewn in both the machine and cross -machine directions, provide sewn seam samples that are oriented in both the machine and cross- machine directions. Replace or repair geosynthetic that is torn or punctured according to the manufacturer’s recommendations.

207.04Geotextile an d Geogrid in Separation and Stabilization Applications.

(a)Surface preparation. Before placing the geotextile remove sharp objects and large rocks. Fill depressions or holes with suitable material to provide a smooth surface. Prepare the surface as follows:

(1)E xisting ground. Cut trees and shrubs flush with the ground surface. Clear the area of vegetation and obstructions according to Sections 201 and 203.

(2)Subgrade. Prepare the subgrade accord ing to Subsections 204.13(b) and (c) .

(3)Subexcavation. Perform subexcavation according to Subsection 204.07.

(b)Geotextile or geogrid placement. Place geogrid on top of geotextile if both are shown at the same elevation in the plans. Place the geosynthetic smooth, taut, and wrinkle free on the underlying surface. Conform to curves. Overlap in the direction of construction. Overlap at least 24 inches at the ends and sides of adjoining sheets or sew the joints according to the approved installation plan. Do not place longitudinal overlaps below anticipated wheel paths. Hold the geosynthetic in place with pins, staples, or piles of cover material.

(c)Backfilling .

(1)First lift plac ement and compaction. Place the specified backfill onto the geotextile or geogrid from the edge of the geosynthetic or from previously placed cover material. Do not operate equipment directly on the geosynthetic. Spread the pile of cover material maintaining a minimum 6-inch lift over the geosynthetic. Avoid sudden stops, starts, or turns of the construction equipment. Fill ruts from construction equipment with additional cover material. Do not blade material down to remove ruts. If rutting exceeds 3 inches during placement, decrease the construction equipment size, decrease the equipment weight, or increase the first lift thickness as directed. Compact according to Subsection 204.11. Do not use sheepsfoot or studded compaction equipment. Compact the cover material with pneumatic- tire or nonvibratory smooth drum rollers.

(2)Subsequent lift placement and compaction. Place subsequent lifts according to Subse ction 204.10. Compact according to Subsection 204.11. Vibratory rollers may be used unless pumping or foundation failures occur. Repair damaged areas and then use only nonvibratory rollers.

207.05Geotextile Filter Applicat ions.

(a)Surface preparation. Before placing the geotextile remove sharp objects and large rocks. Fill depressions or holes with suitable material to provide a smooth surface. Prepare the surface as follows:

(1)Existing ground. Cut trees and shrubs flush with the ground surface. Clear the area of vegetation and obstructions according to Sections 201 and 203. (2) Subgrade. Prepare the subgrade according to Subsections 204.13(b) and (c) .

(3)Subexcavation. Perform subexcavation according to Subsection 204.07.

(b)Geotextile placement. For slope or wave protection, place the long dimension of the geotextile down the slope. For stream bank protection, place the long dimension of the geotextile parallel to the centerline of the channel. Overlap or sew seams at the ends and sides of adjoining sheets.

(1)Overlapping. Overlap the uphill or upstream sheet over the downhill or downstream sheet. For above water applications, overlap the geotextile at least 12 inches. For underwater applications, overlap the geotextile at least 36 inches.

(2)Sewing. Sew the geotextile seam according to the approved installation plan. Offset end joints of adjacent sheets at least 5 feet. Use key trenches or aprons at the crest and toe of slopes to hold the geotextile in place. As an alternative use anchor pins, at least 18 inches long and spaced at 36 inches on center s to hold the geotextile sheets in place.

(c)Backfilling. Place aggregate, slope protection, or riprap on the geotextile starting at the toe of the slope and proceeding upward. Place riprap onto the geotextile from a height of less than 12 inches. Place slope protection rock or aggregate backfill onto the geotextile from a height less than 36 inches. Do not allow stones weighing more than 100 pounds to roll down the slope. In underwater applications, place the geotextile and cover material in the same day.

207.06Geotextile and Geogrid Reinforcement Applications. For MSE retaining walls and reinforced soil slopes, place reinforcement geosynthetics according to Section 255 or 261, as applicable. For deep patch and other reinforcement geosynthetic applications, perform the work as follows:

(a)Surface preparation. Perform subexcavation according to Section 204. Provide a smooth, flat, and firm foundation for the geosynthetic.

(b)Geosynthetic placement. Place the reinforcement geosynthetic with the higher strength direction oriented perpendicular to the road centerline or slope face, as shown in the plans. Place the geosynthetic smooth, taut, and wrinkle free on the underlying surface. Conform to curves. Overlap 24 inches for biaxial geosynthetics in the direction of construction. For uniaxial geogrids, do not splice in the high strength direction, and abut adjacent sheets of geogrid. Hold the geosynthetic in place with pins, staples, or piles of cover material.

(c)Backfilling. Place the specified material onto the geosynthetic from the edge of the geosynthetic or from previously placed cover material. Do not operate equipment directly on the geosynthetic. Spread the material maintaining a minimum 6 -inch lift over the geosynthetic before operating equipment over the geosynthetic. Avoid sudden stops, starts, or turns of the construction equipment. Fill ruts from construction equipment with additional cover material. Do not blade material down to remove ruts. If rutting exceeds 3 inches during placement, decrease the construction equipment size, decrease the equipment weight, or increase the first lift thickness as directed. Compac t according to Subsection 204.11. Do not use sheepsfoot or studded compaction equipment. Compact from the face of slope or wall towards the back of the reinforcement.

207.07Geomembrane Applications. Conduct a preparatory phase meeting at least 7 days before start of geomembrane installation according to Subsection 153.06(a) . Discuss details of the approved submittal according to Subsection 207.03 and observe performance of seam test strips.

(a)Surface preparation. Provide a smooth, flat, firm, unyielding foundation for the geomembrane with no sudden, sharp, or abrupt changes or break in grade. Remove rocks, stones, sticks, sharp objects, and debris protruding more than ½ inch above the prepared surface.

(b)Geomembrane placement. Orient seams parallel to the line of maximum slope. Use sandbags or piles of cover material to hold the geomembrane in place. Do not drive equipment directly on the geome mbrane.

(c)Backfilling. Place the specified backfill within the same work shift that the geomembrane is installed or place enough cover material to keep the geomembrane in place to resist thermal shrinking, expansion, and other deformations. Place backfill onto the edge of previously placed cover material and roll it into place. Do not push material along the geomembrane which can result in damage, stretching, or wrinkling.

207.08Acceptance . Geosynthetics will be evaluated under Subsections 106.02 and 106.03. Submit a production certification with each shipment of geosynthetics. Geosynthetic installation will be evaluated under Subsections 106.02 and 106.04. Sewn joints will be evaluated under Subsection 106.02. Clearing will be evaluated under Section 201. Removal of obstructions will be evaluated under Section 203. Subgrade preparation and subexcavation will be evaluated under Section 204.

Measurement

207.09Measure the Section 207 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring geosynthetics by the square yard, measure each individual layer on a plane parallel to the slope face. Do not measure return wraps at edges of the reinforced areas.

Payment

207.10The accepted quantities will be paid at the contract price per unit of measurement for the Section 207 pay items listed in th e bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 .