1、Designation: D7178 06 (Reapproved 2011)D7178 16Standard Practice forDetermining the Number of Constrictions “m” of Non-Woven Geotextiles as a Complementary Filtration Property1This standard is issued under the fixed designation D7178; the number immediately following the designation indicates the ye
2、ar oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes the procedure used along with
3、existing test method to determine the number of constrictions m ofmechanically bonded non-woven geotextiles, based on thickness, mass per unit area and fiber properties1.2 The number of constrictions is a property of non-woven geotextiles, which is complementary to opening size to predict theirfiltr
4、ation 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 productswith different opening sizes.1.3 Consideration of
5、 the number of constriction is relevant in filtration applications where piping or clogging concerns are tobe controlled with a high level of confidence, that is, for filters applications in critical soils.1.4 This standard is for design purposes only and is not intended for quality control purposes
6、.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Do
7、cuments2.1 ASTM Standards:2D1577 Test Methods for Linear Density of Textile FibersD4439 Terminology for GeosyntheticsD4751 Test Method for Determining Apparent Opening Size of a GeotextileD5199 Test Method for Measuring the Nominal Thickness of GeosyntheticsD5261 Test Method for Measuring Mass per U
8、nit Area of GeotextilesD6767 Test Method for Pore Size Characteristics of Geotextiles by Capillary Flow Test3. Terminology3.1 DefinitionsFor definitions of terms used in this test method, refer to Terminology D4439.3.2 Definitions of Terms Specific to This Standard:3.2.1 constrictionin the non-woven
9、 geotextile, a “window” delimited by three or more fibers, through which soil particlescould migrate.3.2.2 filtration pathsunder the forces induced by fluid flows, soil particles may travel in the geotextile filter along filtrationpaths. Each of these paths is composed of a sequence of constrictions
10、 of various size and shape.3.2.3 number of constrictions, maverage number of constrictions for a filtration path.3.2.4 fiber count, Ta measure of the linear density of the fiber expressed in tex, where 1 tex = 10-6 kg/m.3.2.4.1 Discussion1 This practice is under the jurisdiction ofASTM Committee D35
11、 on Geosynthetics and is the direct responsibility of Subcommittee D35.03 on Permeability and Filtration.Current edition approved June 1, 2011June 1, 2016. Published July 2011 June 2016. Originally published 2006. Last previous version approved 20062011 asD7178D7178 06 (2011).06. DOI: 10.1520/D7178-
12、06R11.10.1520/D7178-16.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard
13、and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases onl
14、y the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1The fiber count is sometime expressed in “Denier” (equivalent to the weight in grams o
15、f a theoretical 9000 meters long fiber). Thevalue in “Tex” can be obtained from the value in Denier considering that 1 Tex = 9 Denier.Denier = 9 Tex.3.2.5 opening sizelargest significant opening of a non-woven geotextile as measured using Test Method D6767.NOTE 1Although Test Method D4751 (Apparent
16、Opening Size) is widely used to characterize geotextiles, it may often not be sufficient for advancedfiltration investigations such as those requiring consideration of the number of constriction as a significant parameter. The “bubble-point” measurementtechnique proposed in Test Method D6767 shall t
17、hus be preferred to AOS per Test Method D4751.4. Summary of Practice4.1 The physical properties of the geotextile are evaluated according to specific procedures and the number of constriction mis determined based on Eq 1.5. Significance and Use5.1 This practice provides a calculation method for dete
18、rmining the number of constrictions m of a non-woven geotextile (orof a layer of a composite material). This standard is not applicable to woven geotextiles, knitted geotextiles, heat-bondedgeotextiles or any other type of geosynthetic.5.2 The number of constriction represents the number of “windows
19、” delimited by three or more fibers, in which soil particlescould migrate. In that regard, it can be basically defined by the following equation: m5 tdcwhere t is the thickness and dc the averagedistance between two constrictions. This value has been found to be relevant to explain the different fil
20、tration behaviors ofnon-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 variousnon-woven geotext
21、iles with similar opening sizes (Test Method D6767).5.4 Interpretation of the significance of m as calculated using this standard shall be done with care as some non-woven structuresmay not reflect the hypothesis used to establish the proposed equation (see Appendix X1 for details).6. Procedure6.1 C
22、ondition specimens at 23 6 2C 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.NOTE 2Although the thickness of non-woven geotextiles is influenced by the normal load, the number of constri
23、ction shall be calculated consideringthe geotextile thickness under 2 kPa for standardization purpose. Practically, the number of constriction is not influenced by the thickness as it representsthe structure of the non-woven (number of “windows” delimited by three or more fibers, in which soil parti
24、cles could migrate as defined in 5.2), whichdoes 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 certificate.Report values by classes of average fiber count associated to the type of polymer as well as th
25、e percentage of each class foundin 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 constrictions m of the geotextile using Eq 1 (dimensionless value). Result must be rounded to thecloses
26、t unit.mi5123=piiti3(kpk 1Tk(1)where:i = specimen number,mi = number of constriction for the geotextile specimen i,i = mass per unit area of the geotextile specimen i (g/m2) as measured in 6.2,ti = thickness of the geotextile specimen i (mm) as measured in 6.2,k = class of fibers with a given fiber
27、count and type of polymer,pk = percentage (in decimal unit, that is, 10 % = 0.1) of fibers from a class of fibers k, andTk = fiber count (tex) associated to a class of fibers k as measured in 6.3.NOTE 3If the fiber count Tk is available in Denier, divide the available value by 9 to obtain the value
28、in Tex.7. Report7.1 Report the following information:7.1.1 State that the number of constriction was calculated as directed in Practice D7178;7.1.2 Complete geotextile identification;7.1.3 Statement of conditioning;7.1.4 Thickness and mass per unit area of the geotextile: individual values and avera
29、ge;7.1.5 Fiber count distribution / polymer as evaluated in 6.3. If it was assumed that only one type of polymer was used tomanufacture the geotextile, state this on report;D7178 1627.1.6 Number of constriction as calculated in 6.3.1; and7.1.7 Report any deviation from the described standard practic
30、e.8. Precision and Bias8.1 Precision and bias has not been established yet.9. Keywords9.1 clogging; constriction; filtration; geotextile; mechanically bonded; non-woven; number of constrictions; opening size;pipingAPPENDIX(Nonmandatory Information)X1. PHYSICAL SIGNIFICANCE OF THE NUMBER OF CONSTRICT
31、IONX1.1 Alternate Equations Describing the Number of ConstrictionX1.1.1 The number of constriction represents the number of “windows” delimited by three or more fibers, in which soil particlescould migrate. In that regard, it can be basically defined by the following equation:m5 tdc(X1.1)where:t = t
32、he geotextile thickness, anddc = the average distance between two constrictions.X1.1.2 Given that the average distance between two constrictions can be expressed by the following equation (1):3dc5 df=12n(X1.2)X1.1.2.1 The porosity of the non-woven geotextile by:n512 t (X1.3)where: = the mass per uni
33、t area,t = the thickness of the non-woven geotextile, and = the polymer specific gravity.X1.1.2.2 Another expression of the number of constriction of non-woven geotextiles is as follows:m5 tdF2 (X1.4)X1.1.3 Fiber count expressed as T5SpidF24 D, it is also possible to define the number of constrictio
34、n of non-woven geotextiles asfollows:m5pit4T (X1.5)3 The boldface numbers in parentheses refer to the list of references at the end of this standard.D7178 163where:pi = 3.14, = mass per unit area,t = thickness, andT = fiber count.X1.2 Constrictions and Filtration Opening Size DistributionsX1.2.1 Aco
35、nceptual definition of the constrictions and filtration opening size distributions of all the filtration paths of a geotextileis presented in Fig. X1.1 (2). Given that the filtration openings are defined as the smallest constrictions of the filtration paths, theirdistribution in size will be proport
36、ionally smaller than the constrictions one. By definition, the smallest opening size (O0) couldnot be smaller than the smallest constriction (C0).X1.3 Significance of the Number of Constrictions with Regard to Opening Size Distribution and Soil FiltrationX1.3.1 Non-woven geotextiles filters having s
37、imilar Filtration Opening Size (which may be considered equal to O100) but differentconstriction numbers may exhibit significantly different filtration behavior for specific situations.X1.3.2 Fig. X1.2 (2) presents the constrictions and openings sizes distributions of two geotextiles having an ident
38、ical opening size(O100), but where the number of constrictions of filter A is smaller than the one of filter B. As a consequence, the maximumconstriction size C100 of filter A is also smaller than the one of filter B.X1.3.3 Using the constriction and opening size distribution curves, it is possible
39、to estimate the probability that a given soilparticle will be retained in or on the geotextile, or be piped:X1.3.3.1 For a soil particle diameter d2 larger than the filter opening size O100, the probability to be trapped into the geotextileincreases as the number of constrictions increases. So filte
40、r B is more likely to trap soil particles with a diameter d2, while theseparticles will be retained on the surface of filter A. If the particle particles with a diameter d2 is part of the soil skeleton, thisskeleton will not be stable, the particles closer to the filter being likely to move downward
41、 into the geotextile structure. For twogeotextiles presenting the same opening size but different numbers of constrictions used to filter a soil made of a skeleton andmovable particles, the geotextile presenting a high number of constrictions could thus lead to an unstable behavior of the soil, thes
42、oil skeleton integrity being not properly supported in critical situations and/or soil / geotextile combinations.X1.3.3.2 For a soil particle diameter d1 lower than the geotextile opening size O100, the probability to be washed out through thegeotextile increases as the m value increases. On the oth
43、er hand, this increased probability to be retained on a low m geotextilecompared to a high m geotextile could eventually lead to the development of the blinding mechanism in critical situations and/orsoil / geotextile combinations.C: constrictionsO: openingsFIG. X1.1 Constriction and Filtration Size
44、 Distribution Curves (2)D7178 164X1.3.4 At the time of preparation of this standard, there was no general agreement regarding the limits that shall be consideredfor filtration design.REFERENCES(1) Giroud, J. P., “Granular Filters and Geotextile Filters,” Keynote Lecture, Proceedings of Geofilters 96
45、, Montral, Qubec, Canada, EcolePolytechnique Montral, 1996, pp. 565-680.(2) Giroud, J. P., “Geotextile Filters: Reliable Design or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 166
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