USACE / NAVFAC / AFCESA / NASA UFGS-31 05 22 (August 2008)
--------------------------
Preparing Activity: USACE (CW) Superseding
UFGS-31 05 22 (April 2006)
UNIFIED FACILITIES GUIDE SPECIFICATIONS
References are in agreement with UMRL dated January 2009
SECTION 31 05 22
GEOTEXTILES USED AS FILTERS
08/08
NOTE: This guide specification covers the requirements for furnishing, hauling,
and placing the geotextile, complete, as specified and shown, and maintaining
the geotextile until placement of the granular filter material, bedding material,
and/or riprap cover is completed and accepted.
Edit this guide specification for project specific requirements by adding, deleting,
or revising text. For bracketed items, choose applicable items(s) or insert
appropriate information.
Remove information and requirements not required in respective project, whether
or not brackets are present.
Comments and suggestions on this guide specification are welcome and should
be directed to the technical proponent of the specification. A listing of technical
proponents, including their organization designation and telephone number, is
on the Internet.
Recommended changes to a UFGS should be submitted as a Criteria Change Request
(CCR).
PART 1 GENERAL
NOTE: This guide specification is to facilitate the preparation and review
of specifications for procurement and installation of woven and nonwoven geotextiles
as filter material. It is based on field performance and the laboratory testing
of a limited number of geotextiles. Geotextiles possess greatly varying engineering
properties and physical characteristics. Such variations require the designer
to decide which testing method and what test criteria are necessary for each
application. The apparent opening size (AOS), percent open area (POA), geotextile
permeability (Kg), and strength test described in the specifications that follow
are physical property tests. While it is acceptable to specify minimum thickness
value where it governs performance, it is inappropriate to use thickness to
identify a geotextile. Result of these tests are used to judge the acceptability
of a geotextile for a particular use. Prospective geotextile suppliers should
furnish these test results before their geotextile will be considered for use,
or before contract specifications are adjusted to permit the use of geotextiles
whose properties are outside the limits imposed by this guide. For severe soil
conditions and/or for a project using a large amount of geotextiles, the specifications
should require that the applicable tests be run during construction, either
at a specific frequency or upon demand of the Contracting Officer. For projects
requiring small amounts of geotextiles under normal soil conditions the physical
properties of the geotextile supported by written authentication from an authorized
representative of the manufacturers may be accepted.
The actual life of geotextiles is not known, and their use in inaccessible areas
must be considered carefully. Therefore geotextiles should not be used as filter
material in toe drains, buried collector system, relief wells, or within any
portions of embankments. Caution is advised in using geotextiles on the upstream
face of earth dams or to wrap permanent piezometers.
Geotextiles are basically inert materials for typical civil engineering applications.
However certain applications may expose the geotextile to chemical or biological
activities that could drastically influence the filtration properties of the
geotextile. Specific site conditions should be reviewed, and if such conditions
exist, testing and specifications should be written to overcome it.
Geotextile strength requirements vary with intended use and construction procedures.
Experience has shown that when a heavier non-woven geotextile is used, the bedding
material can often be reduced in thickness or be completely eliminated. TABLE
I in SI (ENGLISH) UNITS (1) presents the most important geotextile strength
properties. It should be noted that the strength requirements listed are only
a guideline to the minimum values required for survivability. Specific applications
may require additional testing.
Filter design criteria for geotextiles are based on the apparent opening size
(AOS, which is designated as EOS in the previous guide specification), percent
open area (POA, for woven only), geotextile permeability (Kg), and an appropriate
percent passing size of the soil. For piping analysis computations, AOS must
be expressed as an equivalent U.S. standard sieve opening in millimeters. To
assure adequate resistance to reduction in permeability over time (clogging)
and sufficient long term flow through the soil/woven geotextile system, POA
criteria, as expressed in the next note, can be used.
===================================================================
TABLE I
RECOMMENDED GEOTEXTILE STRENGTH REQUIREMENTS IN METRIC UNITS (1)
-------------------------------------------------------------------
GEOTEXTILE | STRENGTH REQUIREMENTS (MINIMUM VALUES)
USE |
-------------------------------------------------------------------
| ASTM D | ASTM D 4355 | ASTM D | ASTM D |
| 4632 | ULTRAVIOLET | 4833 | 4533 |
| TENSILE | DEGRADATION | PUNCTURE | TEAR |
| (N) | AT 500 HRS | (N) | (N) |
| | PERCENT | | |
-------------------------------------------------------------
RIPRAP SLOPE | | | | |
PROTECTION | | | | |
FILTER WITH | | | | |
GREATER THAN | 515 | 50 | 180 | 180 |
102 mm | | | | |
BEDDING | | | | |
------------------------------------------------------------------
RIPRAP SLOPE | | | | |
PROTECTION | | | | |
WITHOUT | 900 | 50 | 360 | 180 |
BEDDING | | | | |
-------------------------------------------------------------------
DRAINAGE | 515 | 50 | 180 | 110 |
TRENCH | | | | |
-------------------------------------------------------------------
SLAB | 515 | 50 | 180 | 110 |
DRAIN | | | | |
-------------------------------------------------------------------
ARTICULATED | | | | |
MATTRESS OR | | | | |
INTERLOCKING | 515 | 50 | 180 | 180 |
BLOCK SLOPE | | | | |
PROTECTION | | | | |
FILTER | | | | |
------------------------------------------------------------------
(1) Strength values are for the weaker principal direction.
===================================================================
TABLE I
RECOMMENDED GEOTEXTILE STRENGTH REQUIREMENTS IN ENGLISH UNITS (1)
-------------------------------------------------------------------
GEOTEXTILE | STRENGTH REQUIREMENTS (MINIMUM VALUES)
USE |
-------------------------------------------------------------------
| ASTM D | ASTM D 4355 | ASTM D | ASTM D |
| 4632 | ULTRAVIOLET | 4833 | 4533 |
| TENSILE | DEGRADATION | PUNCTURE | TEAR |
| (lbs) | AT 500 HRS | (lbs) | (lbs) |
| | PERCENT | | |
-------------------------------------------------------------------
RIPRAP SLOPE | | | | |
PROTECTION | | | | |
FILTER WITH | | | | |
GREATER THAN | 115 | 50 | 40 | 40 |
4 INCHES | | | | |
BEDDING | | | | |
-------------------------------------------------------------------
RIPRAP SLOPE | | | | |
PROTECTION | | | | |
WITHOUT | 200 | 50 | 80 | 40 |
BEDDING | | | | |
-------------------------------------------------------------------
DRAINAGE | | | | |
TRENCH | 115 | 50 | 40 | 25 |
-------------------------------------------------------------------
SLAB | | 50 | 40 | 25 |
DRAIN | 115 | 50 | 40 | 25 |
-------------------------------------------------------------------
ARTICULATED | | | | |
MATTRESS OR | | | | |
INTERLOCKING | 115 | 50 | 40 | 40 |
BLOCK SLOPE | | | | |
PROTECTION | | | | |
FILTER | | | | |
------------------------------------------------------------------
(1) Strength values are for the weaker principal direction.
The designer must specify geotextile properties which will allow retention of
the soil being protected, permit sufficient flow through the textile, and prevent
clogging. The designer should select the AOS, POA, and Kg, based on criteria
in TABLE II. The AOS requirement should be specified as a range, to allow for
manufacturing tolerance. It is preferable to specify a geotextile with opening
as large as allowed by the design criteria. The smallest sieve opening size
of the AOS range should not be smaller than the U.S. Standard sieve size No.
120 (0.125 mm).
TABLE II
GEOTEXTILE FILTER DESIGN CRITERIA
PROTECTED SOIL (1) COEFFICIENT OF
(PERCENT PASSING SOIL (2) PERMEABILITY (3)
NO. 200 SIEVE) PIPING WOVEN NON-WOVEN
< 5 095/D85 < 1 POA 10% Kg 5Ks
5 TO 50 095/D85 < 1 POA 4% Kg 5Ks
50 TO 85 095/D85 < 1 POA 4% Kg 5Ks
095 < 0.212 mm
(No. 70 U.S.
sieve)
95/D85 < 1 Kg 5Ks
095 < 0.125
(No. 120 U.S.
sieve)
(1) Recent experiences have indicated that 095 (i.e. AOS) increased
with increasing relative density, Dr, and it is higher for uniform soil
than well graded soil of similar density and average particle size.
(2) If the protected soil contains appreciable quantities of material
retained on the No. 4 U.S. sieve use only the soil passing the No. 4 U.S.
sieve in selecting the 095 of the geotextile.
(3) Kg is the permeability of the geotextile and Ks is the permeability
of the protected soil.
Satisfactory geotextile performance is greatly dependent on the field preparation
of the surface of the protected soil and the installation procedure.
The following information is related to TABLE 1. Geotextile calculations should
be based on procedure from an accepted reference. Worst placement conditions
should be considered since stresses generated during installation often exceed
post construction stresses.
(1) The requirement of permittivity (as defined in ASTM D 4491) should be chosen
in such a manner that the permeability of the geotextile should always be at
least five times greater than the permeability of the adjacent soil during the
life of the protected earth structure.
(2) The minimum seam strength listed in TABLE 1 is based on the tensile strength
of the parent geotextile material. Seam strength can also be considered as
not less than 90 percent of the unaged grab tensile strength of the geotextile
in the applicable direction.
NOTE: TO DOWNLOAD UFGS GRAPHICS
Figures described below are available on-line for download. Go to http://www.wbdg.org/ccb/NAVGRAPH/graphtoc.pdf
.
Figure 1. Correct geotextile placement for current acting parallel to bank
or for wave attack on the bank.
Figure 2. Placement of geotextile on bank subject to streamflow action. Revetment
materials have not yet been placed on the geotextile.
Figure 3. Geotextile on bank subject to wave attack showing placement of vertical-wall
key trench at toe and top bank. Revetment materials have not yet been placed
on geotextile.
Figure 4. Key trench design used when soil conditions do not permit construction
of vertical walls.
The Designer must comply with the requirements of the following Regulatory Requirements:
U.S. DEPARTMENT OF INTERIOR, BUREAU OF RECLAMATION - 7-2071 (6-48), (1992) Design
Standard No. 13, "Embankment Dams", Chapter 19, "Geotextile"
U.S. DEPARTMENT OF INTERIOR, BUREAU OF RECLAMATION:
EM 1110-2-1601, (1991) "Hydraulic Design of Flood Control Channels"
EM 1110-2-1906, (1970) Laboratory Soil Testing, Appendix V, "Grain-Size Analysis",
paragraph 2d "Procedure", subparagraph (1)(g)
1.1 UNIT PRICES
NOTE: If Section 01 22 00.00 10 MEASUREMENT AND PAYMENT is included in the
project specifications, this paragraph title (UNIT PRICES) should be deleted
from this section and the remaining appropriately edited subparagraphs below
should be inserted into Section 01 22 00.00 10.
1.1.1 Payment
Payment will be made at the contract unit price and will constitute full compensation to the Contractor for providing
all plant, labor, material, and equipment and performing all operations necessary for the complete and satisfactory
installation of the geotextile. The following items are included in the contract unit price for Geotextiles
and will not be counted a second time in the process of determining the extent of geotextile placed: Material
and associated equipment and operation used in laps, seams, or extra length; securing pins and associated material,
equipment, and operations; and material and associated equipment and operations used to provide cushioning layer
of sand or gravel or both to permit increase in allowable drop height of stone. No payment will be made for
geotextiles replaced because of waste, contamination, damage, repair, or due to Contractor fault or negligence.
1.1.2 Measurement
Installed geotextiles will be measured for payment in place to the nearest [_____] square meter feet of protected
area as delineated in the drawings.
1.1.3 Unit of Measure
Unit of measure: [_____] square meter feet.
1.2 REFERENCES
NOTE: This paragraph is used to list the publications cited in the text of
the guide specification. The publications are referred to in the text by basic
designation only and listed in this paragraph by organization, designation,
date, and title.
Use the Reference Wizard's Check Reference feature when you add a RID outside
of the Section's Reference Article to automatically place the reference in the
Reference Article. Also use the Reference Wizard's Check Reference feature
to update the issue dates.
References not used in the text will automatically be deleted from this section
of the project specification when you choose to reconcile references in the
publish print process.
The publications listed below form a part of this specification to the extent referenced. The publications are
referred to within the text by the basic designation only.
[ASTM INTERNATIONAL (ASTM)ASTM D 123(2007) Terminology Relating to TextilesASTM D 4354(1999; R 2004) Sampling of Geosynthetics for TestingASTM D 4355(2007) Deterioration of Geotextiles from Exposure to Light, Moisture and Heat in a Xenon-Arc Type ApparatusASTM D 4491(1999a; R 2004e1) Water Permeability of Geotextiles by PermittivityASTM D 4533(2004) Trapezoid Tearing Strength of GeotextilesASTM D 4632(2008) Grab Breaking Load and Elongation of GeotextilesASTM D 4751(2004) Determining Apparent Opening Size of a GeotextileASTM D 4833(2007) Index Puncture Resistance of Geotextiles, Geomembranes, and Related ProductsASTM D 4873(2002) Identification, Storage, and Handling of Geosynthetic Rolls and SamplesASTM D 4884(1996; R 2003) Strength of Sewn or Thermally Bonded Seams of Geotextiles][U.S. ARMY CORPS OF ENGINEERS (USACE)EM 1110-2-1601(1994; Change 1) Hydraulic Design of Flood Control Channels]1.3 SUBMITTALS
NOTE: Review submittal description (SD) definitions in Section 01 33 00 SUBMITTAL
PROCEDURES and edit the following list to reflect only the submittals required
for the project. Submittals should be kept to the minimum required for adequate
quality control.
A “G” following a submittal item indicates that the submittal requires Government
approval. Some submittals are already marked with a “G”. Only delete an existing
“G” if the submittal item is not complex and can be reviewed through the Contractor’s
Quality Control system. Only add a “G” if the submittal is sufficiently important
or complex in context of the project.
For submittals requiring Government approval on Army projects, a code of up
to three characters within the submittal tags may be used following the "G"
designation to indicate the approving authority. Codes for Army projects using
the Resident Management System (RMS) are: "AE" for Architect-Engineer; "DO"
for District Office (Engineering Division or other organization in the District
Office); "AO" for Area Office; "RO" for Resident Office; and "PO" for Project
Office. Codes following the "G" typically are not used for Navy, Air Force,
and NASA projects.
Choose the first bracketed item for Navy, Air Force and NASA projects, or choose
the second bracketed item for Army projects.
Government approval is required for submittals with a "G" designation; submittals not having a "G" designation
are for [Contractor Quality Control approval.][information only. When used, a designation following the "G"
designation identifies the office that will review the submittal for the Government.] Submit the following in
accordance with Section 01 33 00 SUBMITTAL PROCEDURES:
SD-04 Samples
Geotextile
Geotextile samples for testing, if requested, to determine compliance with the requirements
in this specification, a minimum of [_____][60] days prior to the beginning of installation
of the same textile. Upon delivery of the geotextile, submit duplicate copies of the written
certificate of compliance signed by a legally authorized official of the manufacturer. The
certificate shall state that the geotextile shipped to the site meets the chemical requirements
and exceeds the minimum average roll value listed in TABLE 1. Upon request, supply quality
control and quality assurance tests for the geotextile. Provide all samples from the same production
lot as will be supplied for the contract, of the full manufactured width of the geotextile by
at least 3 m 10 feet long, except that samples for seam strength may be a full width sample
folded over and the edges stitched for a length of at least 1.5 m 5 feet. Samples submitted
for testing shall be identified by manufacturers lot designation. For needle punched geotextile,
the manufacturer shall certify that the geotextile has been inspected using permanent on-line
metal detectors and does not contain any needles.
SD-07 Certificates
Geotextile
[Manufacturer's certification of the geotextile material.] [All brands of geotextile and
all seams to be used will be accepted on the basis of mill certificates or affidavits. Submit
duplicate copies of the mill certificate or affidavit signed by a legally authorized official
from the company manufacturing the geotextile. The mill certificate or affidavit shall attest
that the geotextile meets the chemical, physical and manufacturing requirements stated in this
specification.]
1.4 DELIVERY, STORAGE, AND HANDLING
Deliver only approved geotextile [rolls][, panels, ][_____] to the project site. All geotextile shall be labeled,
shipped, stored, and handled in accordance with ASTM D 4873. No hooks, tongs, or other sharp instruments shall
be used for handling geotextile.
PART 2 PRODUCTS
2.1 MATERIALS
2.1.1 Geotextile
2.1.1.1 General
NOTE: Nonwoven geotextiles are suitable for filtering fine-grained soils whereas
woven or nonwoven are suitable for well graded granular soils.
Provide geotextile that is a [woven][non-woven] pervious sheet of plastic yarn as defined by ASTM D 123 matching
or exceeding the minimum average roll values listed in TABLE 1. Strength values indicated in the table are for
the weaker principal direction.
TABLE 1
MINIMUM PHYSICAL REQUIREMENTS FOR DRAINAGE GEOTEXTILE
------------------------------------------------------------------------
PROPERTY UNITS ACCEPTABLE VALUES TEST METHOD
------------------------------------------------------------------------
GRAP STRENGTH N ASTM D 4632
------------------------------------------------------------------------
SEAM STRENGTH N ASTM D 4632
------------------------------------------------------------------------
PUNCTURE N ASTM D 4833
------------------------------------------------------------------------
TRAPEZOID TEAR N ASTM D 4533
------------------------------------------------------------------------
PERMEABILITY cm/sec ASTM D 4491
------------------------------------------------------------------------
APPARENT OPENING
SIZE U.S. SIEVE ASTM D 4751
------------------------------------------------------------------------
PERMITTIVITY sec -1 ASTM D 4491
------------------------------------------------------------------------
ULTRAVIOLET
DEGRADATION Percent 50 AT 500 Hrs 50 AT 500 Hrs ASTM D 4355
------------------------------------------------------------------------
TABLE 1
MINIMUM PHYSICAL REQUIREMENTS FOR DRAINAGE GEOTEXTILE
------------------------------------------------------------------------
PROPERTY UNITS ACCEPTABLE VALUES TEST METHOD
------------------------------------------------------------------------
GRAP STRENGTH lb ASTM D 4632
------------------------------------------------------------------------
SEAM STRENGTH lb ASTM D 4632
------------------------------------------------------------------------
PUNCTURE lb ASTM D 4833
------------------------------------------------------------------------
TRAPEZOID TEAR lb ASTM D 4533
------------------------------------------------------------------------
PERMEABILITY cm/sec ASTM D 4491
------------------------------------------------------------------------
APPARENT OPENING
SIZE U.S. SIEVE ASTM D 4751
------------------------------------------------------------------------
PERMITTIVITY sec -1 ASTM D 4491
------------------------------------------------------------------------
ULTRAVIOLET
DEGRADATION Percent 50 AT 500 Hrs 50 AT 500 Hrs ASTM D 4355
------------------------------------------------------------------------
2.1.1.2 Geotextile Fiber
Fibers used in the manufacturing of the geotextile shall consist of a long-chain synthetic polymer composed of
at least 85 percent by weight of polyolefins, polyesters, or polamides. Add stabilizers and/or inhibitors to
the base polymer, if necessary to make the filaments resistant to deterioration caused by ultraviolet light and
heat exposure. Reclaimed or recycled fibers or polymer shall not be added to the formulation. Geotextile shall
be formed into a network such that the filaments or yarns retain dimensional stability relative to each other,
including the edges. Finish the edges of the geotextile to prevent the outer fiber from pulling away from the
geotextile.
2.1.2 Seams
NOTE: Most geotextiles are manufactured in widths of 1.8 to 5.5 m (six to eighteen
feet), but to reduce the number of overlaps, wider sections may be produced
by attaching narrow sections together. Pre-assembled sections of 11-m (36-foot)
widths or more are preferred to keep the number of overlaps to a minimum.
Sew the seams of the geotextile with thread of a material meeting the chemical requirements given above for geotextile
yarn or bond the seams by cementing or by heat. Attach the sheets of geotextile at the factory or another approved
location, if necessary, to form sections not less than [_____] meter [_____] feet wide. Test seams in accordance
with method ASTM D 4884. The strength of the seam shall be not less than 90 percent of the required grab tensile
strength of the unaged geotextile in any principal direction.
2.1.3 Securing Pins
NOTE: The use of security pins should be restricted as much as possible since
holes in geotextile allow pin boils to form and remove material from beneath
geotextile and cause failure of system.
Secure the geotextile to the embankment or foundation soil by pins to prevent movement prior to placement of
revetment materials. Other appropriate means to prevent movement such as staples, sand bags, and stone could
also be used. Insert securing pins through both strips of overlapped geotextile along the line passing through
midpoints of the overlap. Remove securing pins as placement of revetment materials are placed to prevent tearing
of geotextile or enlarging holes. Maximum spacing between securing pins depends on the steepness of the embankment
slope. The maximum pins spacing shall be equal to or less than the values listed in TABLE 2. When windy conditions
prevail at the construction site, increase the number of pins upon the demand of the Contracting Officer. Anchor
terminal ends of the geotextile with key trench or apron at crest, toe of the slope and upstream and downstream
limits of installation.
TABLE 2
MAXIMUM SPACING FOR SECURING PINS
----------------------------------------------------------
EMBANKMENT SPACING, meter
----------------------------------------------------------
STEEPER THAN 1V ON 3H 0.6
----------------------------------------------------------
1V ON 3H TO 1V ON 4H 1.0
----------------------------------------------------------
FLATTER THAN 1V ON 4H 1.5
----------------------------------------------------------
TABLE 2
MAXIMUM SPACING FOR SECURING PINS
----------------------------------------------------------
EMBANKMENT SPACING, feet
----------------------------------------------------------
STEEPER THAN 1V ON 3H 2
----------------------------------------------------------
1V ON 3H TO 1V ON 4H 3
----------------------------------------------------------
FLATTER THAN 1V ON 4H 5
----------------------------------------------------------
2.2 INSPECTIONS, VERIFICATIONS, AND TESTING
2.2.1 Manufacturing and Sampling
Geotextiles and factory seams shall meet the requirements specified in TABLE 1. [Perform conformance testing
in accordance with the manufacturers approved quality control manual.][Randomly sample geotextiles in accordance
with ASTM D 4354 (Procedure Method A). Sample factory seams at the frequency specified in ASTM D 4884.]
2.2.2 Site Verification and Testing
NOTE: The need for, and amount of, site verification testing should be based
on the severity of site conditions and the amount of textile being placed.
Collect samples at approved locations upon delivery to the site [at the request of the Contracting Officer][in
accordance with ASTM D 4354 (Procedure Method B)][at a frequency of once per 9290 square meters 100,000 square
feet]. Test samples to verify that the geotextile meets the requirements specified in TABLE 1. Identify samples
by manufacturers name, type of geotextile, lot number, roll number, and machine direction. Perform testing at
an approved laboratory. Submit test results from the lot under review for approval prior to deployment of that
lot of geotextile. Rolls which are sampled shall be immediately rewrapped in their protective covering.
PART 3 EXECUTION
3.1 SURFACE PREPARATION
Prepare surface, on which the geotextile will be placed, to a relatively smooth surface condition in accordance
with the applicable portion of this specification and shall be free from obstruction, debris, depressions, erosion
feature, or vegetation. Remove any irregularities so as to ensure continuous, intimate contact of the geotextile
with all the surface. Any loose material, soft or low density pockets of material, shall be removed; erosion
features such as rills, gullies etc. shall be graded out of the surface before geotextile placement.
3.2 INSTALLATION OF THE GEOTEXTILE
NOTE: This paragraph describes installation in an open area and on generally
planar surfaces. For installation of geotextiles in drainage systems or about
collector pipes, additional specification requirements may need to be added.
The use of geotextiles to wrap collector pipes should be avoided whenever possible.
Minimum overlaps should be specified at 300 to 450 mm (12 to 18 inches) depending
on the specified orientation of the overlap to the direction of wave attack,
velocity, or seepage. For under-water placement, minimum overlap should be
900 mm (3 feet).
Geotextiles will bridge small surface features in the slope and allow erosion
to occur beneath the geotextile. Surface drainage should be directed away from
the top of slope to prevent erosion under the geotextile. Surface flow should
be brought downslope at controlled points such as lined ditches.
3.2.1 General
Place the geotextile in the manner and at the locations shown. At the time of installation, reject the geotextile
if it has defects, rips, holes, flaws, deterioration or damage incurred during manufacture, transportation or
storage.
3.2.2 Placement
NOTE: The placement of the geotextile relative to this paragraph may follow
the following general procedures. (FIGURES referenced in this note are available
on-line, see the note above).
(1) For current acting parallel to the bank the geotextile will be placed with
the long dimension parallel to the current (Fig. 1a). Geotextile placement
must be started from the bottom up with upper strips overlapping lower strips,
and the upstream strips must overlap the downstream strips. The overlaps at
the end of strips will be staggered at least 1.5 m. (5 feet). Revetment and
geotextile materials should be extended at least below the mean low water to
minimize erosion at the toe (Fig. 2). If construction schedule permits, a period
of low streamflow should be selected for the geotextile installation.
(2) When revetment material and geotextile filter are selected to protect against
wave attack, the geotextile strips must be placed vertical to the slope of the
bank with the upper strips overlapping the lower strips (Fig. 1b). The geotextile
must be keyed at the toe to prevent uplift or undermining (Fig. 3). The key
trench should be located below the mean low water to prevent erosion of the
soil adjacent to the trench. When it is not possible to maintain vertical trench
walls, the geotextile must be keyed to an excavated trench with stable slopes
(Fig. 4). A key at the top of the bank will be installed where there is an
overbank drainage problem.
Allowing the geotextile to drape or be free of high tensile stress during placement
will require larger quantities of geotextiles than the actual slope length.
Place the geotextile with the long dimension [parallel] [perpendicular] to the [centerline of the channel][shoreline][trench]
and laid smooth and free of tension, stress, folds, wrinkles, or creases. Place the strips to provide a minimum
width of [_____] mm inches of overlap for each joint. The placement procedure requires that the length of the
geotextile be approximately [_____] percent greater than the slope length. Adjust the actual length of the geotextile
used based on initial installation experience. Temporary pinning of the geotextile to help hold it in place
until the [bedding layer][riprap] is placed will be allowed. Remove the temporary pins as the [bedding][granular
material][riprap] is placed to relieve high tensile stress which may occur during placement of material on the
geotextile. Design protection of riprap shll be in compliance with EM 1110-2-1601. Perform trimming in such
a manner that the geotextile is not damaged in any way.
3.3 PROTECTION
NOTE: All geotextiles can be damaged if stone is dropped on it from a height
greater than 900 mm (3 feet). Some geotextiles can be damaged with lesser drop
heights. When stone is heavy and angular it may cause punctures in the geotextile
even if dropped from a height of 300 mm (1 foot). Tension in the geotextile
must be minimized to prevent puncture.
Protect the geotextile at all times during construction from contamination by surface runoff; remove any geotextile
so contaminated and replaced with uncontaminated geotextile. Replace any geotextile damaged during its installation
or during placement of [granular filter materials][bedding materials][riprap] at no cost to the Government.
Schedule the work so that the covering of the geotextile with a layer of the specified material is accomplished
within [_____][7] calendar days after placement of the geotextile. Failure to comply shall require replacement
of geotextile. Protect the geotextile from damage prior to and during the placement of riprap or other materials.[
This may be accomplished by limiting the height of drop to less than 300 mm 1 foot, by placing a cushioning layer
of sand or gravel on top of the geotextile before placing the material, or other methods deemed necessary. Care
should be taken to ensure that the utilized cushioning materials will not impede the flow of water.] Before
placement of riprap or other materials, demonstrate that the placement technique will not cause damage to the
geotextile. In no case shall any type of equipment be allowed on the unprotected geotextile.
3.4 PLACEMENT OF CUSHIONING MATERIAL
Perform placing of cushioning material in a manner to ensure intimate contact of the geotextile with the prepared
surface and with the cushioning material. The placement shall also be performed in a manner that will not damage
the geotextile including tear, puncture, or abrasion. On sloping surfaces place the cushioning material from
the bottom of the slopes upward. During placement, the height of the drop of riprap material shall not be greater
than 300 mm 12 inches. Uncover any geotextile damaged beneath the cushioning material, as necessary, and replaced
at no cost to the Government.
3.5 OVERLAPPING AND SEAMING
3.5.1 Overlapping
NOTE: In general, overlapping is sufficient where the primary purpose is to
hold the material in place during installation. However, where the design requires
the geotextile to resist tensile stresses, seams should be sewn. A 300-mm (12-inch)
overlap specified in this section is considered minimum for all cases. The
Contractor has the option of field sewing instead of overlapping.
The overlap of geotextile [rolls] [panels] [_____] shall be [300][600] [900][_____] mm [12][24][36][_____] inches
. Appropriate measures will be taken to ensure required overlap exists after cushion placement.
3.5.2 Sewn Seams
NOTE: The Designer must specifiy appropriate seam test requirements. ASTM
D 1683, the previously used test standard, has been discontinued with no replacement
designated.
High strength thread should be used so that seam test conforms to ASTM D 4884. The thread shall meet the chemical,
ultraviolet, and physical requirements of the geotextile, and the color shall be different from that of the geotextile.
The seam strength shall be equal to the strength required for the geotextile in the direction across the seam.
Overlapping J-type seams are preferable over prayer-type seams as the overlapping geotextile reduces the chance
of openings to occur at the seam. Use double sewing, specially for field seams, to provide a safety factor against
undetected missed stitches.
3.6 [FIELD TESTING
NOTE: The need for field testing should be based on the size and importance
of the project. Field testing should be performed if the geotextile will be
in tension.
Field test geotextile[ in tension].]