355 ALASKA 2020 SECTION 631 GEOTEXTILE FOR SUBSU RFACE DRAINAGE AND E ROSION CONTROL
631-1.01 DESCRIPTION . Prep are ground surfac e, and furnish and place geotextiles for
subsurface drai nage and erosion control, as sho wn on the Plans.
631-2.01 MATERIALS. Use materials that conform to the following for the class specified in the
bid sche dule: Geotextiles and Sewn Seam Strength Subs ection 729-2.01 Sewing Thread. Use high strength polypropylene, or polyester. Do not use nylon thread. Use thread of contrasting color to that of the geotextile itself.
631-3.01 Constructi On Requirements.
1.Surface Pr eparati on. Prepare ground s urface by removi ng stu mps, brush, boulders, and sharp objects. Fill holes and ruts over 3 inches deep, with material shown on the Plans or as approved by the Engineer. Construct smooth and stable trench walls.
2.Geotextile Place ment. Unroll geotextile directly onto the prepared surface. Stretch geotextile to remove any creases, folds or wrinkles. Place geotextile in a manner which will ensure intimate contact between the trench wall and the geotextile (i.e., no voids, folds, or wrinkles). The geotextile may be held in place with securing pins at 3- foot spacing along all edges (but not closer than 2 inches from the edge) to prevent movement during construction. Do not expo se geotextiles to sunlight for longer than 14 days after removal of protective cover ing. Do not allow geotextile rolls to get wet prior to installation.
a.Subs urface Drai nage. In trenche s, after placing the geotextile and material shown on the Plans , fold the geotextile over the top of the material shown on the Plans to produce a minimum overlap of 12 inches, for trenche s great er than 12 inches wide. In trenches less than 12 inches wide, make the overl ap equal to the width of the trench. Then cover the ge otextile with the s ubsequ ent cou rse of material.
b.Erosion Control. Place and anchor geotextile on the approved surface so it will not be torn or excessively stretc hed by placem ent of the overlying mater ials. Secure the geotextile to the s lope but secure it loosely enough so that the geotextile will not tear when riprap or other cover material is placed on the geotextile. The geotextile shall not be keyed at the top of the slope until the riprap or other cover material is in place at the top of the slope. Anch or the terminal end s of the geotextile using key trenches or aprons with a minimum of 24 inches depth into the soil substrate at the crest and toe of slope, or as shown on the Plans. Place geotextile with the machine direction parall el to the direction of water flow (normally parallel to the slope for erosion control runoff and wave action, and parallel to the stream or channel).
3.Joining. Join geotextile by sewing or overla pping.
a.Sew seam s with a Butterfly or J-Seam using a double thread chain stitch (lock stitch). Bring adjacent sections of geotextile togeth er and fold so that the stitching penetrates four layers of geotextile for the full seam length. Make the stitching line 1-1/4 inches (±1/ 4 inc h) from the folded edge of the seam and at least 1/2 inch from the free edge of the geotextile. Sew seams so that they can be easily inspected by the Engineer or representative. Illustrati ons showing correct stitch formation and seam configurations are provid ed in Figure 1-2 (page 1- 28) of the FHWA publ ication, Geosynthetic Design & Co nstruction Guidel ines, FHWA -NHI-07-092, August 2008. 356 ALASKA 2020 Conform both factory and field sewn seams to the strength requirements of Table 1 as outlined in the AASHTO M288 for subsurface drainage and erosion control applications.
b.Overla p geotextile secti ons by a minimum of 3 feet at all longitudinal and transverse joints. Overlap successive geotextile she ets in the dir ection of flow so that the upstream sheet is placed over the downstream sh eet and/or upsl ope ov er do wnslope. In trenc hes, where overlapp ed seams are con structed in the longitudinal trench direction, make the overlap equal to the width of the trench.
4.Placement of Cover Material . Foll owing p lacem ent of the g eotextile on the prepared surf ace, place cover material of the type shown on the Plans. Place the cover material and armor from the bottom to the top of the slope using method s wh ich minimize tearing and/ or excessive stretchi ng of the geotextile. In unde rwater appl ications, place the geotextile and the required thickn ess of cover material in the same day. Mainta in prope r overlap and geotextile continuity. Do not exceed the allowable drop heigh ts for c over material shown in Tabl e 631- 1. Do not allow stones with a weight of more than 100 pounds t o roll down the slope on the geotextile. Do not grade the slope in a way that will disturb the cover material or armor stone once it has been placed. Backfill all voids in the riprap or other cover material, which allows the geotextile to be visible, wit h material shown on the Plans, so that the geotextile is completely covered. TABLE 631-1 ALLOWABLE DROP HEIGHT FOR GEOTEXTILE * Protected geotextile is defined as having a gravelly covering (cushion layer) at least 6 inches thick. ** If stones greater than 250 pounds must be dropped or if a height of drop greater than 3 feet is required, then perform field trials to determine the minimum cushion thickness and/or maximum height of safe drop without damaging the geotextile. Maintain a minimum depth of 12 inches of cover material between the geotextile and the wheels or tracks of the construction equipment.
5.Geotextile Repair. Should the geotextile be torn, punctured, or the overlaps or sewn joints disturbed – as evidenced by visible geotextile damage – remove the backfill around the damaged area and repair or replace the damaged area at no additional expense to the Stat e. Make repairs to the damaged area with a patch of the same type of geotextile originally placed. Overlay torn area with geotextile with a minimum 3 foot overlap arou nd the edge s of the torn area. Ensure that the patch remain s in place when mater ial is placed over the affected area.
631-4.01 METHOD OF M EASUREMENT. By multiplying plan neat line width by the measured
length in final position parallel to installation centerline along the ground surface No allowance will be made f or geotextile in key trenc hes or for overlap, whet her at joints o r patc hes.
631-5.01 BASIS OF PA YMENT. Payment will be made at the contract unit price per square yard.
Material used to fill ruts and holes will be paid for under separate materials pay items at the unit price for the type of material used. INDIVID UAL STONE Max. Weig ht (lbs) ALLOWABLE DROP HE IGHT (ft) UNP ROT ECTED GEOTEXTILE PROT ECTED GEOTEXTILE * < 5 3 3 5-250 0 3 > 250 0 0** 357 ALASKA 2020 Payment will be made under: PAY ITEM Item Number Item Description Unit 631.0001. ____ Geotextile, Drainage, Class 2 SY 631.0002. ____ Geotextile, Erosion Control, Class 1 SY 358 ALASKA 2020 SECTION 632 PAVING FABRIC
632-1.01 DESCRIPTION . Furnish and install geotextile paving fabric where shown on the Plans.
632-2.01 MATERIALS. Use materials that conform to the following:
Paving Fabric Subsection 729- 2.03 Emulsified Asphalt Subsection 702- 2.03
632-3.01 Constructio N Requirements.
1.Surface Preparation. Prepare the surface on which the fabric is to be placed as follows:
a.Remove excess asphalt material, loose aggregate, and other foreign materials from the surface.
b.Fill all potholes and cracks wider than 1/4 inch with emulsified asphalt (CSS -1) sand slurry.
2.Application of Sealant . Apply asphalt sealant (emulsified asphalt, tack coal) by distributor meeting all requirements set forth under Subsection 402- 3.02. Apply asphalt sealant uniformly at 0.20 to 0.30 gallons per square yard and at a temperat ure shown in Table 702- 1 or as recommended by the Paving Fabric manufacturer. Do not apply asphalt material on a wet surface or when the ambient air temperature is below 45 °F or when other conditions would prevent proper application.
3.Fabric Laydown Equipment . Use approved mechanical laydown equipment to place fabric.
4.Fabric Placement . Place fabric directly on top of the asphalt sealant (emulsified asphalt, tack coat) before the sealant has cooled and lost its tackiness. Lay fabric in full rolls without wrinkles and/or folds. Place the fabric per the manufacturer’s recommendations. Overlap geotextile joints to ensure full closure of the joint, but do not exceed 6 inches of overlap. Overlap transverse joints in the direction of paving. Apply 0.20 gallons per square yard of additional asphalt sealant beneath all fabric joints. Remove and replace damaged geotextiles. Removal and replacement of damaged geotextiles is subsidiary to Section 632 Pay Items.
5.Bituminous Surface Course Overlay . Place the bituminous surface course closely following the fabric laydown to avoid exposure of uncovered fabric overnight or to traffic or inclement weather. Do not allow the temperature of the hot -mix asphalt to exceed manufacturer’s recommendations. If asphalt sealant bleeds through the fabric before the placement of the overlay, apply sand or bituminous surface course evenly over the affected area to prevent fabric pick -up by construction equipment. Prevent paver or other construction equipment from turning and/or pivotin g on the fabric.
632-4.01 METHOD OF M EASUREMENT. By multiplying plan neat line width by the measured
length in final position parallel to installation centerline along the ground surface. No allowance will be made f or overlap, whet her at joints o r patc hes.
632-5.01 BASIS OF PA YMENT. Payment will be made under:
PAY ITEM Item Number Item Description Unit 632.0001.____ Paving Fabric SY
Source: Alaska Standard Specifications for Highway Construction, 2020 Edition. Pages 383–385 of 584.