ASTM D7178-22

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Designation: D7178 − 16 D7178 − 22
Standard Practice for
Determining the Number of Constrictions “m” of Non-Woven
Geotextiles as a Complementary Filtration Property
This standard is issued under the fixed designation D7178; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—A legend was added editorially to Eq X1.4 in X1.1.2.2 in July 2016.
1. Scope
1.1 This practice describes the procedure used along with existing test methodmethods to determine the number of constrictions
m of mechanically bonded non-woven geotextiles, based on thickness, mass per unit area, and fiber properties
1.2 The number of constrictions is a property of non-woven geotextiles, which is complementary to opening size to predict their
filtration behavior. It can be used to differentiate non-woven geotextiles with similar opening sizes but different structures
(thickness, weight, fiber diameter, etc.). However, more research is needed to assess its significance when comparing two products
with different opening sizes.
1.3 Consideration of the number of constrictionconstrictions is relevant in filtration applications where piping or clogging
concerns are to be controlled with a high level of confidence, that is, for filtersfilter applications in critical soils.
1.4 This standard is for design purposes only and is not intended for quality control purposes.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1577 Test Methods for Linear Density of Textile Fibers
D4439 Terminology for Geosynthetics
D4751 Test Methods for Determining Apparent Opening Size of a Geotextile
D5199 Test Method for Measuring the Nominal Thickness of Geosynthetics
D5261 Test Method for Measuring Mass per Unit Area of Geotextiles
D6767 Test Method for Pore Size Characteristics of Geotextiles by Capillary Flow Test
This practice is under the jurisdiction of ASTM Committee D35 on Geosynthetics and is the direct responsibility of Subcommittee D35.03 on Permeability and Filtration.
Current edition approved June 1, 2016Dec. 1, 2022. Published June 2016December 2022. Originally published in 2006. Last previous version approved 2011 in 2016 as
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D7178 – 06 (2011).D7178 – 16 . DOI: 10.1520/D7178-16E01.10.1520/D7178-22.
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D7178 − 22
3. Terminology
3.1 Definitions—For definitions of terms used in this test method, practice, refer to Terminology D4439.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 constriction—constriction, n—in the non-woven geotextile, a “window” delimited by three or more fibers, through which
soil particles could migrate.
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3.2.2 fiber count, T, n—a measure of the linear density of the fiber expressed in tex, where 1 tex = 10 kg/m.
3.2.2.1 Discussion—
The fiber count is sometime expressed in “Denier” (equivalent to the weight in grams of a theoretical 9000 m long fiber). The value
in “tex” can be obtained from the value in Denier considering that 1 Denier = 9 tex.
3.2.3 filtration paths—paths, n—under the forces induced by fluid flows, soil particles may travel in the geotextile filter along
filtration paths. Each of these paths is composed of a sequence of constrictions of various size and shape.
3.2.4 number of constrictions, m—m, n—average number of constrictions for a filtration path.
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3.2.4 fiber count, T—a measure of the linear density of the fiber expressed in tex, where 1 tex = 10 kg/m.
3.2.4.1 Discussion—
The fiber count is sometime expressed in “Denier” (equivalent to the weight in grams of a theoretical 9000 meters long fiber). The
value in “Tex” can be obtained from the value in Denier considering that 1 Denier = 9 Tex.
3.2.5 opening size—size, n—largest significant opening of a non-woven geotextile as measured using Test Method D6767.
NOTE 1—Although Test Method D4751 (Apparent Opening Size) is widely used to characterize geotextiles, it may often not be sufficient for advanced
filtration investigations such as those requiring consideration of the number of constriction as a significant parameter. The “bubble-point” measurement
technique proposed in Test Method D6767 shall thus be preferred to AOS per Test Method D4751.
3.2.5.1 Discussion—
Although Test Method D4751 (Apparent Opening Size) is widely used to characterize geotextiles, it may often not be sufficient
for advanced filtration investigations such as those requiring consideration of the number of constrictions as a significant parameter.
The “bubble-point” measurement technique proposed in Test Method D6767 shall thus be preferred to AOS per Test Method
D4751.
4. Summary of Practice
4.1 The physical properties of the geotextile are evaluated according to specific procedures and the number of constrictioncon-
strictions m is determined based on Eq 1.
5. Significance and Use
5.1 This practice provides a calculation method for determining the number of constrictions m of a non-woven geotextile (or of
a layer of a composite material). This standard is not applicable to woven geotextiles, knitted geotextiles, heat-bonded geotextiles,
or any other type of geosynthetic.
5.2 The number of constrictionconstrictions represents the number of “windows” delimited by three or more fibers, in which soil
t
particles could migrate. In that regard, it can be basically defined by the following equation: m5 where t is the thickness and
d
c
d the average distance between two constrictions. This value has been found to be relevant to explain the different filtration
c
behaviors of non-woven geotextiles with similar opening sizes but different structures for various soil conditions (see Appendix
X1 for details).
5.3 This value will be used in filtration research to evaluate the prediction of filtration efficiency and effectiveness of various
non-woven geotextiles with similar opening sizes (Test Method D6767).
D7178 − 22
5.4 Interpretation of the significance of m as calculated using this standard shall be done with care, as some non-woven structures
may not reflect the hypothesis used to establish the proposed equation (see Appendix X1 for details).
6. Procedure
6.1 Condition specimens at 23 6 2°C2 °C and 65 % relative humidity for not less than 24 h.
6.2 Determine the mass per unit area and thickness of the geotextile according to Test Methods D5261 and D5199.
6.2.1 Although the thickness of non-woven geotextiles is influenced by the normal load, the number of constrictions shall be
calculated considering the geotextile thickness under 2 kPa for standardization purposes. Practically, the number of constrictions
is not influenced by the thickness as it represents the structure of the non-woven (number of “windows” delimited by three or more
fibers, in which soil particles could migrate as defined in 5.2), which does not depend on the normal load.
NOTE 2—Although the thickness of non-woven geotextiles is influenced by the normal load, the number of constriction shall be calculated considering
the geotextile thickness under 2 kPa for standardization purpose. Practically, the number of constriction is not influenced by the thickness as it represents
the structure of the non-woven (number of “windows” delimited by three or more fibers, in which soil particles could migrate as defined in 5.2), which
does not depend on the normal load.
6.3 Determine the fiber count of the fibers per Test Methods D1577 using the data available from MQA or suppliers from the
supplier’s certificate. Report values by classes of average fiber count associated to the type of polymer as well as the percentage
of each class found in the geotextile sample (that is, respective percentages of polypropylene / xx tex, polypropylene / yy tex,
polyester / zz tex, etc.).
6.3.1 Calculate the number of constricti
...