for Highway Construction Page 558 of 71 5 SECTION 640 – CONSTRUCTION GEOTEXTILES
640.01 Description.
Provide and install geotextile.
640.02 Materials.
Provide materials as specified in 718.
640.03 Construction Requirements.
A.Shipment and Storage . Place the geotextile in a dry place off the ground and protected from damage and maintain in an opaque, heavy -duty protective covering during periods of shipment and storage.
B.Placement . Grade the area to be covered to a smooth, uniform condition without obstructions, depressions, and debris. Spread the geotextile immediately ahead of the covering operation. Do not drag the geotextile on the ground or mishandle it. Place the geotextile loosely and without wrinkles so the placement of the overlying material will not tear the geotextile. Hold the geotextile in place with pins, staples, or small piles of fill or rock. Lap or sew the geot extile, as specified, at the ends and sides of adjoining sheets. Place the cover material on the geotextile so at least 6 to 18 inches of material is between the vehicle or equipment tires or tracks and the geotextile, depending on the survivability of the geotextile and the weight of the construction equipment. Do not spread overlying material closer than 2 feet from geotextile edges before forming overlaps for installations requiring adjacent geotextile placements, so that subsequent overlaps can be constructed without having to push material back from geotextile edges. Cover the geotextile with the specified cover material as soon as possible. Do not allow the geotextile to be exposed to the elements for more than 30 calendar days for ultraviolet stabilized geotextiles and 7 days for geotextiles that have not been ultraviolet stabilized.
C.Soft Ground. Limit construction vehicle size and weight so rutting in the initial lift above the geotextile is 3 inches or less deep when geotextile is placed over soft ground. Do not turn vehicles on the first lift above the geotextile. Do not end- dump the cover material directly on the geotextile. Limit compaction of the first lift above the geotextile over soft ground to routing of placing and spreading equipment only. Do not allow sheep- foot type equipment on the first lift. Closely observe subsequent lifts during compaction, and if foundation failures occur during compaction operations, use lightweight compaction equipment. Use pegs, pins, or the manufacturer’s recommended method as needed to hold the geotextile in place until the specified cover m aterial is placed. Do not drop cover material on unprotected geotextile from a height greater than 3 feet above the geotextile surface.
D.Seams. Use sewn seams that consist of 2 parallel rows of stitching. Ensure the 2 rows of stitching are ½ inch apart with a to lerance of ¼ inch and do not cross, except for restitching. Provide a lock -type stitch. If a flat or prayer seam is used, the minimum seam allowance (i.e., the minimum distance from the geotextile edge to the stitch line nearest to that edge) is 1½ inches. Ensure the minimum seam allowance for other seam types is 1 inch. for Highway Construction Page 559 of 71 5 Obtain approval of the seam, stitch type, and the equipment used to perform the stitching before work start begins. Use a “J” seam with 2 passes of a lock- type stitch with at least 3 stitches per inch. The Contractor may use the prayer seam (flat) for repair of damaged in- place geotextiles. Sew the seams with high -strength polyolefins, polyester, or Kevlar thread that is as resistant to deterioration as the geotextile being sewn. Provide thread color that contrasts with the geotextile color. Do not use nylon threads. Ensure the strength of the seam is at least 90 percent of the minimum required tensile strength for the intended application as specified in 718.05, 718.06, 718.07, 718.08, and 718.09. Obtain approval before production field stitching or seaming.
E.Repairs. If the geotextile is torn, punct ured, or the overlaps or sewn joints disturbed, as evidenced by visible geotextile damage, subgrade pumping, intrusion, or roadbed distortion, remove the backfill around the damaged or displaced area and repair or replace the damaged geotextile at no cost to the Department. Place a patch of the same type geotextile over the damaged area and overlap the existing geotextiles at least 2 feet from the edge of the damaged area, except for pavement overlay geotextiles. Patch overlay geotextiles as specified in 640.03.I. Where geotextile seams are required to be sewn, repair damaged sheets by sewing. Sew seams as specified in 640.03.D.
F.Underground Drainage . Construct underdrains . Place the geotextile to conform loosely to the shape of the trench. Overlap the geotextile at least 12 inches at longitudinal and transverse joints or sew the geotextile joints. In trenches less than 12 inches wide, overlap the width of the trench. When drainage geotextile s are placed under or over a horizontal or sloping surface (e.g., subgrade, in conjunction with drain blankets) use the geotextiles that meet the construction survivability requirements of subgrade separation geotextiles.
G.Riprap /Erosion Control . Construct geotextiles under riprap or rock buttresses as specified and as specified. Overlap the geotextile at least 2 feet at longitudinal and transverse joints or sew the geotextile at joints at the time of manufacture to form geotextile widths as specified. If overlapped, place the geotextile so the upstream strip of geotextile is on top of the next downstream strip. Where placed on slopes, lap each strip over the next downhill strip and as specifie d. Lap geotextile up against structures one half the riprap layer depth. Anchor geotextile upstream edges, downstream edges, top edges not against structures and bottom edges as specified . Start placemen t of aggregate and/or riprap on the geotextile at the toe of the slope and proceed upwards. Show the combination of the rock -fill drop height and the aggregate cushion thickness are adeq uate to not puncture or damage the geotextile when placing the riprap or rock -fill. Where an aggregate cushion i s required, place it at least 6 inches thick. The limits specified in Table 640.03- 1 apply. for Highway Construction Page 560 of 71 5 Table 640.03- 1 – Riprap Drop Crite ria Size of Riprap Material Maximum Drop Directly onto Geotextile Onto Aggregate Cushion Blanket ≤ 200 lb Rock 3 feet 5 feet > 200 lb Rock 0 3 feet After placing the riprap, backfill voids in the riprap face so the geotextile is completely covered. Do not grade slopes after riprap placement if grading results in stone movement directly on the geotextile. Do not allow stones weighing more than 110 pounds to roll down the slope. The Engineer may reduce drop heights if geotextile damage from the stones dropping is evident. When geotextile is placed on slopes steeper than 2H:1V, place the stones on the slope without free- fall.
H.Subgrade Separation. Prepare the subgrade as specified in 205 or as directed. Overlap adjacent geotextiles at least 2 feet at longitudinal and transverse joints or sew the geotextiles to form the widths specified. Type I refers to moderate survivability conditions and Type II refers to high survivability conditions as defined in 718.07.
I.Pavement Overlay s. Construct pavement overlay s as follows:
1.Weather Limitations . Do not place sealant and geotextile when the roadway surface or weather conditions would prevent proper construction. Do not place paving grade asphalt sealant until the minimum air temperature is at least 50°F.
2.Initial Surface Preparation. Prepare the pavement surface before the sealant is applied as specified in 401.03. In addition, clean cracks exceeding ⅛ inch width and fill with suitable bituminous crack filler. Allow the crack filling material to cure in accordance with the manufacturer’s written instructi ons before placing the geotextile. Place leveling courses before placing the geotextile.
3.Asphalt Sealant Application. Provide asphalt sealant that is the type and grade specified. Spread the sealant material using a pressure distributor as specified in 406.03. Uniformly spray -apply the asphalt sealant to the prepared dry pavement surface at the rate recommended by the geotextile manufacturer and as approved. Do not allow the distributor tank temperature to exceed 320°F for paving grade asphalt cements. Spray the asphalt sealant 6 inches wider than the paving geotextile. Apply the sealant only as far in front of the geotextile installation as is appropriate to ensure a tacky surface at the time of geotextile placement. Place the geotextile on the sealant while it is hot. Do not allow traffic on the sealant.
4.Geotextile Placement . Protect the geotextile from moisture. Place the geotextile using mechanical or manual laydown equipment capable of providing a smooth installation with minimal wrinkling or for Highway Construction Page 561 of 715 folding. Slit wrinkles or folds larger than 1 inch and lay flat. Shingle- lap tran sverse joints and slit folds or wrinkles in the direction of the paving operation. Provide overlap sufficient to ensure closure, but not more than 6 inches. Use brooms or pneumatic rollers to maximize geotextile contact with the pavement surface. Apply additional hand- placed sealant material at laps. Limit traffic on the placed geotextile to neces sary construction equipment and emergency vehicles. Avoid abrupt starts and stops. Remove and replace damaged geotextile with the s ame type of geotextile, and shingle lap the overlaps in the direction of paving at no cost to the Department.
5.Overlay Placement . Ensure overlay placement closely follows geotextile placement. Do not allow windrow asphal t on the geotextile ahead of the paving machine. Avoid abrupt starts or stops and keep turnings of paver and other equipment to the minimum to avoid geotextile damage.
640.04 Method of Measurement.
The Engineer will measure ac ceptably completed work to the nearest square yard of surface area covered. A separate measurement will not be made for const ruction of laps, seams , joints , or patches unless the Engineer orders more than the specified lap, in which case the added lap width will be measured. The Engineer will compute the square yards of drainage geotextile in the trench by multiplying the length of the trench where geotextile is used by the averag e perimeter of the constructed trench’s typical section.
640.05 Basis of Payment .
The Department will pay for accepted quantities at the contract unit prices as follows: Pay Item Pay Unit Drainage Geotex tile ................................................................................ SY Riprap /Erosion Control Geotextile .......................................................... SY Subgrade Separation Geotextile ............................................................. SY Pavement Overlay Geotextile ................................................................. SY If the Engineer directs geotextiles with properties more stringent than specified, the Department will allow price adjustment s for difference in material cost only. for Highway Construction Page 562 of 71 5 SECTION 641 – BIAXIAL GEOGRID
641.01 Description.
Provide biaxial geogrid and all accessories, equipment, and labor necessary to reinforce subgrade or subbase, or similar applications as specified or as directed.
641.02 Materials.
Provide the geogrid manufacturer’s certified test results attesting the geogrid meets the specifications. Provide geogrid certifications signed by the manufacturer’s authorized agent, including the following information about each geogrid to be used:
1.Manufacturer’s name, address, and phone number.
2.Full product name.
3.Style or product code number.
4.Geogrid roll and/or lot number.
5.Geogrid polymer type.
6.Testing agency name, address, and phone number.
7.Certified te st dates and results.
8.Published physical dimensions. Provide the test dates on the certification. As a means of identification, provide tags on the product rolls with the manufacturer’s name, full product name, style or product code number, and lot and/or roll number, which will permit field determination of the product delivered to the project site is covered by the certification. Ensure the certified copy of the test results includes each test result and each mean average roll value. The Department will not accept the certification without the certified test results. The Engineer will obtain geogrid samples for testing. Each sample will be taken beyond the first wrap and will be at least 6 feet long and extend across the full geogrid roll width. The samples will be labeled with the manufacturer and full product name, style or product code number, lot and roll number, and sampling date.
A.Geogrid Property Requirements . Provide biaxial geogrid and associated components that meet the requirements in Table 641.02- 1. Ensure the biaxial geogrid consists of a regular network of connected longitudinal and transverse polymer elements with aperture geometry sufficient to allow significant mechanical interlock with the surrounding materials. Constr uct in single or multiple layers meeting the requirements in Table 641.02- 1. Table 641.02- 1 Geogrid Property Requirements Minimum Value (a) Property Test Method Type I Type II Type III Tensile Strength @ 5% strain , (lb/ft) ASTM D6637 550 800 1200 Tensile Strength ASTM D6637 275 400 550
Source: Idaho Standard Specifications for Highway Construction, 2023 Edition. Pages 594–597 of 768.