1、Designation: D7178 161Standard 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 year oforiginal adoption or
2、, 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.1NOTEA legend was added editorially to Eq X1.4 in X1.1.2.2 in July 2016.1. Scope1.1 This pr
3、actice describes the procedure used along withexisting test method to determine the number of constrictionsm of mechanically bonded non-woven geotextiles, based onthickness, mass per unit area and fiber properties1.2 The number of constrictions is a property of non-wovengeotextiles, which is complem
4、entary to opening size to predicttheir filtration behavior. It can be used to differentiate non-woven geotextiles with similar opening sizes but differentstructures (thickness, weight, fiber diameter, etc.). However,more research is needed to assess its significance whencomparing two products with d
5、ifferent opening sizes.1.3 Consideration of the number of constriction is relevantin filtration applications where piping or clogging concerns areto be controlled with a high level of confidence, that is, forfilters applications in critical soils.1.4 This standard is for design purposes only and is
6、notintended for quality control purposes.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory
7、 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D1577 Test Methods for Linear Density of Textile FibersD4439 Terminology for GeosyntheticsD4751 Test Method for DeterminingApparent Opening Sizeof a GeotextileD5199 Test Method for Measuring the Nominal Thicknessof GeosyntheticsD52
8、61 Test Method for Measuring Mass per Unit Area ofGeotextilesD6767 Test Method for Pore Size Characteristics of Geotex-tiles by Capillary Flow Test3. Terminology3.1 DefinitionsFor definitions of terms used in this testmethod, refer to Terminology D4439.3.2 Definitions of Terms Specific to This Stand
9、ard:3.2.1 constrictionin the non-woven geotextile, a “win-dow” delimited by three or more fibers, through which soilparticles could migrate.3.2.2 filtration pathsunder the forces induced by fluidflows, soil particles may travel in the geotextile filter alongfiltration paths. Each of these paths is c
10、omposed of a sequenceof constrictions of various size and shape.3.2.3 number of constrictions, maverage number of con-strictions for a filtration path.3.2.4 fiber count, Ta measure of the linear density of thefiber expressed in tex, where 1 tex = 10-6kg/m.3.2.4.1 DiscussionThe fiber count is sometim
11、e expressedin “Denier” (equivalent to the weight in grams of a theoretical9000 meters long fiber). The value in “Tex” can be obtainedfrom the value in Denier considering that 1 Denier = 9 Tex.3.2.5 opening sizelargest significant opening of a non-woven geotextile as measured using Test Method D6767.
12、NOTE 1Although Test Method D4751 (Apparent Opening Size) iswidely used to characterize geotextiles, it may often not be sufficient foradvanced filtration investigations such as those requiring consideration ofthe number of constriction as a significant parameter. The “bubble-point”measurement techni
13、que proposed in Test Method D6767 shall thus bepreferred to AOS per Test Method D4751.4. Summary of Practice4.1 The physical properties of the geotextile are evaluatedaccording to specific procedures and the number of constrictionm is determined based on Eq 1.1This practice is under the jurisdiction
14、 of ASTM Committee D35 on Geosyn-thetics and is the direct responsibility of Subcommittee D35.03 on Permeability andFiltration.Current edition approved June 1, 2016. Published June 2016. Originallypublished 2006. Last previous version approved 2011 as D7178 06 (2011). DOI:10.1520/D7178-16E01.2For re
15、ferenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We
16、st Conshohocken, PA 19428-2959. United States15. Significance and Use5.1 This practice provides a calculation method for deter-mining the number of constrictions m of a non-woven geotex-tile (or of a layer of a composite material). This standard is notapplicable to woven geotextiles, knitted geotext
17、iles, heat-bonded geotextiles or any other type of geosynthetic.5.2 The number of constriction represents the number of“windows” delimited by three or more fibers, in which soilparticles could migrate. In that regard, it can be basicallydefined by the following equation: m5tdcwhere t is thethickness
18、 and dcthe average distance between two constric-tions. This value has been found to be relevant to explain thedifferent filtration behaviors of non-woven geotextiles withsimilar opening sizes but different structures for various soilconditions (see Appendix X1 for details).5.3 This value will be us
19、ed in filtration research to evaluatethe prediction of filtration efficiency and effectiveness ofvarious non-woven geotextiles with similar opening sizes (TestMethod D6767).5.4 Interpretation of the significance of m as calculatedusing this standard shall be done with care as some non-wovenstructure
20、s may not reflect the hypothesis used to establish theproposed equation (see Appendix X1 for details).6. Procedure6.1 Condition specimens at 23 6 2C and 65 % relativehumidity for not less than 24 h.6.2 Determine the mass per unit area and thickness of thegeotextile according to Test Methods D5261 an
21、d D5199.NOTE 2Although the thickness of non-woven geotextiles is influencedby the normal load, the number of constriction shall be calculatedconsidering the geotextile thickness under 2 kPa for standardizationpurpose. Practically, the number of constriction is not influenced by thethickness as it re
22、presents the structure of the non-woven (number of“windows” delimited by three or more fibers, in which soil particles couldmigrate as defined in 5.2), which does not depend on the normal load.6.3 Determine the fiber count of the fibers per Test MethodsD1577 using the data available from MQA or supp
23、lierscertificate. Report values by classes of average fiber countassociated to the type of polymer as well as the percentage ofeach class found in the geotextile sample (that is, respectivepercentages of polypropylene / xx tex, polypropylene / yy tex,polyester / zz tex, etc.).6.3.1 Calculate the num
24、ber of constrictions m of the geo-textile using Eq 1 (dimensionless value). Result must berounded to the closest unit.mi5123 =iti3(kpk1Tk(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,t
25、i= thickness of the geotextile specimen i (mm) as mea-sured in 6.2,k = class of fibers with a given fiber count and type ofpolymer,pk= percentage (in decimal unit, that is, 10 % = 0.1) offibers from a class of fibers k, andTk= fiber count (tex) associated to a class of fibers k asmeasured in 6.3.NOT
26、E 3If the fiber count Tkis available in Denier, divide the availablevalue by 9 to obtain the value in Tex.7. Report7.1 Report the following information:7.1.1 State that the number of constriction was calculated asdirected in Practice D7178;7.1.2 Complete geotextile identification;7.1.3 Statement of
27、conditioning;7.1.4 Thickness and mass per unit area of the geotextile:individual values and average;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;7.1.6 Number of constriction as
28、 calculated in 6.3.1; and7.1.7 Report any deviation from the described standardpractice.8. Precision and Bias8.1 Precision and bias has not been established yet.9. Keywords9.1 clogging; constriction; filtration; geotextile; mechani-cally bonded; non-woven; number of constrictions; openingsize; pipin
29、gD7178 1612APPENDIX(Nonmandatory Information)X1. PHYSICAL SIGNIFICANCE OF THE NUMBER OF CONSTRICTIONX1.1 Alternate Equations Describing the Number ofConstrictionX1.1.1 The number of constriction represents the number of“windows” delimited by three or more fibers, in which soilparticles could migrate
30、. In that regard, it can be basicallydefined by the following equation:m 5tdc(X1.1)where:t = the geotextile thickness, anddc= the average distance between two constrictions.X1.1.2 Given that the average distance between two con-strictions can be expressed by the following equation (1):3dc5df=1 2 n(X
31、1.2)X1.1.2.1 The porosity of the non-woven geotextile by:n 5 1 2t(X1.3)where: = the mass per unit area,t = the thickness of the non-woven geotextile, and = the polymer specific gravity.X1.1.2.2 Another expression of the number of constrictionof non-woven geotextiles is as follows:m 5 tdF2(X1.4)where
32、:dF= fiber diameter.X1.1.3 Fiber count expressed as T5SdF24D, it is alsopossible to define the number of constriction of non-wovengeotextiles as follows:m 5 t4T(X1.5)where: = 3.14, = mass per unit area,t = thickness, andT = fiber count.X1.2 Constrictions and Filtration Opening Size Distribu-tionsX1.
33、2.1 A conceptual definition of the constrictions andfiltration opening size distributions of all the filtration paths ofa geotextile is presented in Fig. X1.1 (2). Given that thefiltration openings are defined as the smallest constrictions ofthe filtration paths, their distribution in size will be p
34、roportion-ally smaller than the constrictions one. By definition, thesmallest opening size (O0) could not be smaller than thesmallest constriction (C0).X1.3 Significance of the Number of Constrictions withRegard to Opening Size Distribution and Soil Fil-trationX1.3.1 Non-woven geotextiles filters ha
35、ving similar Filtra-tion Opening Size (which may be considered equal to O100) butdifferent constriction numbers may exhibit significantly differ-ent filtration behavior for specific situations.X1.3.2 Fig. X1.2 (2) presents the constrictions and openingssizes distributions of two geotextiles having a
36、n identicalopening size (O100), but where the number of constrictions offilterAis smaller than the one of filter B.As a consequence, themaximum constriction size C100of filter A is also smaller thanthe one of filter B.X1.3.3 Using the constriction and opening size distributioncurves, it is possible
37、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 d2larger than the filteropening size O100, the probability to be trapped into thegeotextile increases as the number of constrictions increases.So filter B
38、 is more likely to trap soil particles with a diameterd2, while these particles will be retained on the surface of filterA. If the particle particles with a diameter d2is part of the soilskeleton, this skeleton will not be stable, the particles closer tothe filter being likely to move downward into
39、the geotextilestructure. For two geotextiles presenting the same opening sizebut different numbers of constrictions used to filter a soil madeof a skeleton and movable particles, the geotextile presenting ahigh number of constrictions could thus lead to an unstable3The boldface numbers in parenthese
40、s refer to the list of references at the end ofthis standard.C: constrictionsO: openingsFIG. X1.1 Constriction and Filtration Size Distribution Curves (2)D7178 1613behavior of the soil, the soil skeleton integrity being notproperly supported in critical situations and/or soil / geotextilecombination
41、s.X1.3.3.2 For a soil particle diameter d1lower than thegeotextile opening size O100, the probability to be washed outthrough the geotextile increases as the m value increases. Onthe other hand, this increased probability to be retained on alow m geotextile compared to a high m geotextile couldevent
42、ually lead to the development of the blinding mechanismin critical situations and/or soil / geotextile combinations.X1.3.4 At the time of preparation of this standard, there wasno general agreement regarding the limits that shall be consid-ered for filtration design.REFERENCES(1) Giroud, J. P., “Gra
43、nular Filters and Geotextile Filters,” KeynoteLecture, Proceedings of Geofilters 96, Montral, Qubec, Canada,Ecole Polytechnique 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:/ 1615
