1、 Reference number ISO/TR 20432:2007(E) ISO 2007TECHNICAL REPORT ISO/TR 20432 First edition 2007-12-01 Guidelines for the determination of the long-term strength of geosynthetics for soil reinforcement Lignes directrices pour la dtermination de la rsistance long terme des gosynthtiques pour le renfor
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6、m either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO/TR 20432:2007
7、(E) ISO 2007 All rights reserved iii Contents Page Foreword iv 1 Scope1 2 Normative references1 3 Terms, definitions, abbreviated terms and symbols1 3.1 Terms and definitions .1 3.2 Abbreviated terms.2 3.3 Symbols3 4 Design procedure 4 4.1 Introduction4 4.2 Design lifetime .4 4.3 Causes of degradati
8、on 5 4.4 Design temperature .5 5 Determination of long-term (creep) strain.5 5.1 Introduction5 5.2 Extrapolation6 5.3 Time-temperature superposition methods .6 5.4 Isochronous curves.7 5.5 Weathering, chemical and biological effects8 6 Determination of long-term strength .8 6.1 Tensile strength.8 6.
9、2 Reduction factors 8 6.3 Modes of degradation .8 7 Creep rupture.9 7.1 Introduction9 7.2 Measurement of creep rupture: conventional method 10 7.3 Curve fitting (conventional method)11 7.4 Curve fitting for time-temperature block shifting of rupture curves 12 7.5 Strain shifting and the stepped isot
10、hermal method.13 7.6 Extrapolation and definition of reduction factor or lifetime15 7.7 Residual strength.15 7.8 Reporting of results.15 7.9 Procedure in the absence of sufficient data .15 8 Installation damage .16 8.1 General16 8.2 Data recommended16 8.3 Calculation of reduction factor.17 8.4 Proce
11、dure in the absence of direct data .17 9 Weathering, chemical and biological degradation.19 9.1 Introduction19 9.2 Data recommended for assessment19 9.3 Weathering.19 9.4 Chemical degradation .20 9.5 Biological degradation28 10 Determination of long-term strength .28 10.1 Factor of safety f s .28 10
12、.2 Design for residual strength.29 11 Reporting29 Bibliography 30 ISO/TR 20432:2007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Stan
13、dards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also t
14、ake part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees
15、is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when
16、 a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for example), it may decide by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely infor
17、mative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or
18、all such patent rights. ISO/TR 20432 was prepared by Technical Committee ISO/TC 221, Geosynthetics. TECHNICAL REPORT ISO/TR 20432:2007(E) ISO 2007 All rights reserved 1 Guidelines for the determination of the long-term strength of geosynthetics for soil reinforcement 1 Scope This Technical Report pr
19、ovides guidelines for the determination of the long-term strength of geosynthetics for soil reinforcement. This Technical Report describes a method of deriving reduction factors for geosynthetic soil-reinforcement materials to account for creep and creep rupture, installation damage and weathering,
20、and chemical and biological degradation. It is intended to provide a link between the test data and the codes for construction with reinforced soil. The geosynthetics covered in this Technical Report include those whose primary purpose is reinforcement, such as geogrids, woven geotextiles and strips
21、, where the reinforcing component is made from polyester (polyethylene terephthalate), polypropylene, high density polyethylene, polyvinyl alcohol, aramids and polyamides 6 and 6,6. This Technical Report does not cover the strength of joints or welds between geosynthetics, nor whether these might be
22、 more or less durable than the basic material. Nor does it apply to geomembranes, for example, in landfills. It does not cover the effects of dynamic loading. It does not consider any change in mechanical properties due to soil temperatures below 0 C, nor the effect of frozen soil. The Technical Rep
23、ort does not cover uncertainty in the design of the reinforced soil structure, nor the human or economic consequences of failure. Any prediction is not a complete assurance of durability. 2 Normative references The following referenced documents are indispensable for the application of this document
24、. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 10318, Geosynthetics Terms and definitions 3 Terms, definitions, abbreviated terms and symbols 3.1 Terms and definitions For the purpo
25、ses of this document, the terms and definitions given in ISO 10318 and the following apply. 3.1.1 long-term strength load which, if applied continuously to the geosynthetic during the service lifetime, is predicted to lead to rupture at the end of that lifetime 3.1.2 long-term strain total strain pr
26、edicted in the geosynthetic during the service lifetime as a result of the applied load ISO/TR 20432:2007(E) 2 ISO 2007 All rights reserved3.1.3 reduction factor factor (W 1) by which the tensile strength is divided to take into account particular service conditions in order to derive the long-term
27、strength NOTE In Europe, the term partial factor is used. 3.1.4 characteristic strength 95 % (two-sided) lower confidence limit for the tensile strength of the geosynthetic, approximately equal to the mean strength less two standard deviations NOTE This should be assured by the manufacturers own qua
28、lity assurance scheme or by independent assessment. 3.1.5 block shifting procedure by which a set of data relating applied load to the logarithm of time to rupture, all measured at a single temperature, are shifted along the log time axis by a single factor to coincide with a second set measured at
29、a second temperature 3.1.6 product line series of products manufactured using the same polymer, in which the polymer for all products in the line comes from the same source, the manufacturing process is the same for all products in the line, and the only difference is in the product mass per area or
30、 number of fibres contained in each reinforcement element 3.2 Abbreviated terms CEG carboxyl end group DSC differential scanning calorimetry HALS hindered amine light stabilizers HDPE high density polyethylene HPOIT high pressure oxidation induction time LCL lower confidence limit MARV minimum avera
31、ge roll value OIT oxidation induction time PA polyamide PET polyethylene terephthalate PP polypropylene PTFE polytetrafluorethylene PVA polyvinyl alcohol RF CHreduction factor to allow for chemical and biological effects RF CRreduction factor to allow for the effect of sustained static load RF IDred
32、uction factor to allow for the effect of mechanical damage RF Wreduction factor to allow for weathering SIM stepped isothermal method TTS time-temperature shifting ISO/TR 20432:2007(E) ISO 2007 All rights reserved 3 3.3 Symbols A itime-temperature shift factor b agradient of Arrhenius graph d 50mean
33、 granular size of fill d 90granular size of fill for 90 % pass (10 % retention) f sfactor of safety G, H parameters used in the validation of temperature shift linearity (see 7.4) m gradient of line fitted to creep rupture points (log time against load); inverse of gradient of conventional plot of l
34、oad against log time. M nnumber averaged molecular weight n number of creep rupture or Arrhenius points P applied load R 1ratio representing the uncertainty due to extrapolation R 2ratio representing the uncertainty in strength derived from Arrhenius testing S sqsum of squares of difference of log (
35、time to rupture) and straight line fit S xx , S xy , S yysums of squares as defined in derivation of regression lines in 9.4.3 0standard deviation used in calculation of LCL t time, expressed in hours t 90time to 90 % retained strength t Ddesign life t degdegradation time during oxidation t indinduc
36、tion time during oxidation t LCLLCL of time to a defined retained strength at the service temperature t max longest observed time to creep rupture, expressed in hours t n 2Students t for n 2 degrees of freedom and a stated probability t Rtime to rupture, expressed in hours t stime to a defined retai
37、ned strength at the service temperature T load per width T Bbatch tensile strength (per width) T charcharacteristic strength (per width) (see 6.1) T xunfactored long-term strength (see 9.4.3) ISO/TR 20432:2007(E) 4 ISO 2007 All rights reservedT Dlong-term strength per width (including factor of safe
38、ty) T DRresidual strength jtemperature of accelerated creep test Ktemperature T LCLLCL of T chardue to chemical degradation sservice temperature x abscissa: on a creep rupture graph the logarithm of time, in hours x mean value of x x iabscissa of an individual creep rupture point x ppredicted time t
39、o rupture y ordinate: on a creep rupture graph, applied load expressed as a percentage of tensile strength, or a function of applied load y 0value of y at 1 h (log t = 0) y mean value of y y iordinate of an individual creep rupture point y 0value of y at time 0, derived from the line fitted to creep
40、 rupture points 4 Design procedure 4.1 Introduction The design of reinforced soil structures generally requires consideration of the following two issues: a) the maximum strain in the reinforcement during the design lifetime; b) the minimum strength of the reinforcement that could lead to rupture du
41、ring the design lifetime. In civil engineering design, these two issues are referred to as the serviceability and ultimate limit state respectively. Both factors depend on time and can be degraded by the environment to which the reinforcement is exposed. 4.2 Design lifetime A design lifetime, t D ,
42、is defined for the reinforced soil structure. For civil engineering structures this is typically 50 to 100 years. These durations are too long for direct measurements to be made in advance of construction. Reduction factors have therefore to be determined by extrapolation of short-term data aided, w
43、here necessary, by tests at elevated temperatures to accelerate the processes of creep or degradation. ISO/TR 20432:2007(E) ISO 2007 All rights reserved 5 4.3 Causes of degradation Strain and strength may be changed due to the effects of the following: mechanical damage caused during installation; s
44、ustained static (or dynamic) load; elevated temperature; weathering while the material is exposed to light; chemical effects of natural or contaminated soil. 4.4 Design temperature The design temperature should have been defined for the application in hand. In the absence of a defined temperature or
45、 of site specific in-soil temperature data, the design temperature should be taken as the temperature which is halfway between the average yearly air temperature and the normal daily air temperature for the hottest month at the site. If this information is not available, 20 C should be used as the d
46、efault value. Many geosynthetic tests are performed at a standard temperature of (20 2) C. If the design temperature differs, appropriate adjustments should be made to the measured properties. This Technical Report does not cover the effects of temperatures below 0 C (see Clause 1). 5 Determination
47、of long-term (creep) strain 5.1 Introduction The design specification may set a limit on the total strain over the lifetime of the geosynthetic, or on the strain generated between the end of construction and the service lifetime. In the second case, the time at “end of construction” should be define
48、d, as shown in Figure 1. When plotted against log t, even a one-year construction period should have negligible influence on the creep strain curve beyond 10 years. Levels of creep strain encountered in the primary creep regime (creep rate decreasing with time) are thought not to adversely affect st
49、rength properties of geosynthetic reinforcement materials. ISO/TR 20432:2007(E) 6 ISO 2007 All rights reservedKey 1 Laboratory creep test 5 New time = 0 for post construction creep 2 Load ramp period on wall 6 Wall construction time 3 Load ramp period in creep test X Time 4 Loading and creep of reinforcement in wall Y Strain Figure 1 Conceptual illustration for comparing the creep measured in walls to laboratory creep data 5.2 Extrapolation Creep strain should be measured according to ISO 13431 and plotted as
