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1、BRITISH STANDARD BS 6906-5: 1991 Methods of test for Geotextiles Part 5: Determination of creep Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 This British Standard, having been prepared under the direction of the Textiles an
2、d Clothing Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 29 March 1991 BSI 02-1999 The following BSI references relate to the work on this standard: Committee reference TCM/35 Draft for comment 89/39360 DC ISBN 0 580 19272 5 Committees
3、responsible for this British Standard The preparation of this British Standard was entrusted by the Textiles and Clothing Standards Policy Committee (TCM/-) to Technical Committee TCM/35, upon which the following bodies were represented: Association of Consulting Engineers British Polyolefin Textile
4、s Association British Textile Technology Group Chemical Industries Association Department of Transport Department of Transport (Transport and Road Research Laboratory) ERA Technology Ltd. Federation of Civil Engineering Contractors Institution of Civil Engineers Lambeg Industrial Research Associatio
5、n Ministry of Agriculture, Fisheries and Food Ministry of Defence Society of Engineers Incorporated Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 BSI 02-1999i Contents
6、 Page Committees responsibleInside front cover Forewordii 1Scope1 2Definitions1 3Principle1 4Number of tests1 5Apparatus1 6Conditioning and testing atmosphere2 7Test specimens2 8Procedure2 9Results3 10Test report3 Appendix A Guidance on accuracy of test5 Figure 1 Strain/time relationship3 Publicatio
7、n(s) referred toInside back cover Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 ii BSI 02-1999 Foreword This Part of BS 6906 has been prepared under the direction of the Textiles and Clothing Standards Policy Committee, and
8、forms Part 5 of a comprehensive British Standard on methods of test for geotextiles. Geotextiles are being used increasingly in the reinforcement of soil structures and earthworks. An important characteristic of these materials, as of all plastics, is that their strain under a constant load is a fun
9、ction of time, i.e. they exhibit marked creep characteristics, in that the application of load may lead ultimately to rupture. These characteristics are also affected by environmental factors, in particular, temperature. Information on creep is essential for any consideration of the use of geotextil
10、es as reinforcement. The method described uses 50 mm wide specimens of woven textiles and corresponding samples of geogrids or sheathed strips. The specimen is narrower than the 200 mm width used for tensile testing (BS 6906-1) and has been chosen in this way in order to reduce the expense of long-t
11、erm testing. However, the creep of a conventional woven material arises from two sources: the creep of the warp in tension and the relaxation of the crimp in the warp due to creep in the weft. A 50 mm wide specimen will provide data representative of wider material provided that the friction between
12、 warp and weft is sufficent to maintain tension in the weft over the greater part of the specimen width. If the weft becomes completely slack the subsequent creep may be an underestimation of the creep of a wider specimen. Materials that exhibit large lateral contractions under tensile load, such as
13、 nonwovens, will need to be tested at greater widths. Creep data are not generally required in the cross direction of woven materials. For woven materials part of the extension on loading arises from a straightening of the weave structure and is relatively variable, while the subsequent time-depende
14、nt elongation, which is due to creep of the fibres, is more consistent. This method therefore requires application of a pre-load. Since the loads to be applied are percentages of the tensile strength, before carrying out this test, it is necessary to determine the tensile strength using the method i
15、n BS 6906-1. In soil the creep of the geotextile is likely to be reduced because of transfer of the load to the soil. In-soil testing is, however, difficult to carry out reproducibly. The air environment represents a controlled and more clearly definable test, the results of which are conservative w
16、ith regard to the behaviour of the material in service and which may also be used as the basis for estimating the performance in stress-relaxation and under other conditions of complex load. Information on accuracy of the test is given in Appendix A. Other Parts of BS 6906 are as follows. Part 1: De
17、termination of the tensile properties using a wide width strip; Part 2: Determination of the apparent pore size distribution by dry sieving; Part 3: Determination of water flow normal to the plane of the geotextile under a constant head; Part 4: Determination of the puncture resistance (CBR puncture
18、 test); Part 6: Determination of resistance to perforation (cone drop test); Part 7: Determination of in-plane waterflow; Part 8: Determination of sand-geotextile frictional behaviour by direct shear. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy,
19、(c) BSI BS 6906-5:1991 BSI 02-1999iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Sum
20、mary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside fr
21、ont cover. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv blank Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 BSI 02-19991 1 Scope This Part of BS 6906 describes
22、 a method for determining the load-strain-time relationship of geotextiles at a given temperature from a series of constant load tests. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 6906, the fol
23、lowing definitions apply. 2.1 gauge length the distance in the direction of the applied load between two fixed lines on the specimen drawn perpendicular to that direction, measured after application of the pre-tension 2.2 strain the percentage change in gauge length after application of load, includ
24、ing both that which occurs during loading and that which occurs after the load has been applied 2.3 decade of time the interval between a specified time and its multiple of ten, for example between 100 h and 1 000 h 2.4 isochronous curve a curve which indicates the strain of a material under load fo
25、r a specified time, plotted as load against strain NOTECurves for a range of times are generally plotted on the same diagram. 2.5 load the load in newtons per metre width applied to the specimen, including a pre-tension which is applied at commencement of the test 3 Principle A test specimen is clam
26、ped by jaws at either end across its width. A constant load is applied to the specimen. Strain is measured at specified time intervals. NOTEThe time to rupture may also be determined. 4 Number of tests Creep tests shall be carried out at loads of 20 %, 30 %, 40 % and 60 % of the maximum load per uni
27、t width for the material determined in accordance with BS 6906-1. Tests at additional loads may be appropriate for some materials. 5 Apparatus 5.1 Loading apparatus, consisting of a loading frame sufficiently strong so as not to deform or vibrate when in use. It shall provide access for the specimen
28、 to be mounted, the load to be correctly applied, and strain monitored. The connections between jaws and loading apparatus shall have sufficient freedom (e.g. universal joints) to ensure that the load is applied uniformly across the width of the specimen. The jaws shall grip the specimen with suffic
29、ient firmness to allow minimum slippage. They shall not cause damage nor produce areas of weakness outside the gauge length (see BS 6906-1). Throughout the test, the load shall be known and maintained constant to within 1 %. Where the load is applied by means of weights, with or without a lever, no
30、load cell is necessary provided that the weights and lever ratio have been calibrated previously and that the lever has been balanced with the associated jaw in place. The pre-tension shall be 1.0 0.2 % of the maximum load per unit width determined in accordance with BS 6906-1. NOTE 1In designing le
31、ver type apparatus particular attention should be paid to the limits on lever movement necessary to maintain this tolerance. NOTE 2This apparatus has been selected as a simple means of establishing zero strain although it is recognized as not ideal. 5.2 Extensometer(s), to give strain measurements.
32、Strain of the geotextile under load shall be measured between two lines drawn across the width of the specimen, parallel to each other and to the jaws and at a minimum spacing of 100 mm. If the mass of the extensometer equipment exceeds 1 % of the applied load an appropriate correction shall be made
33、 to the load. In general, two extensometers are necessary on opposite sides and ends of the specimen, from which the average reading will compensate for alignment errors. The extensometer shall allow for a resolution of 0.0002 (0.02 %) strain, and its range shall be selected such that it will accomm
34、odate material extension during at least the first hour of testing without exceeding its limits of calibration and without adjustment. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 2 BSI 02-1999 6 Conditioning and testing at
35、mosphere Unless otherwise specified, the test specimens shall be conditioned, and the test conducted in the standard temperate atmosphere for testing textiles defined in BS 1051, i.e. at a relative humidity of 65 2 % and a temperature of 20 2 C. Any departure from these conditions, for example due t
36、o power failure, shall be noted in the final report. NOTE 1The requirement for a specified relative humidity may be relaxed or omitted, if it can be shown that the material is not sensitive to humidity. NOTE 2Testing at other temperatures will often be required. Recommended additional temperatures a
37、re 10 2 C, 40 2 C and 60 2 C. 7 Test specimens For geotextile fabrics, take specimens at random from different positions across the width of the laboratory sample. Unless otherwise specified, take no specimens nearer than 100 mm from the selvedge or edge of the geotextile. Cut specimens parallel to
38、the warp (or machine direction) of the geotextile. Test specimens shall be 50 mm wide, and sufficiently long to allow a separation of 200 mm between the jaws. NOTEFor woven geotextiles that fray, cut each specimen 10 mm wider than the final width and then remove an equal number of threads from each
39、side to obtain the finished dimension. This helps maintain the specimen integrity during the test. For geomeshes or geogrids choose a specimen width that contains a whole number of ribs and at least one row of nodes or cross-members within the gauge length. Where appropriate, draw four parallel line
40、s running the full width of the specimen, perpendicular to the length dimension, the inner two separated by 100 mm and the outer two by 200 mm. Examine specimens for any signs of damage or inperfections. If any specimens are rejected, this shall be noted. Condition each test specimen for at least 48
41、 h in the test environment (see clause 6). Do not subject the specimen to any stress or strain which could affect its subsequent performance. 8 Procedure 8.1 Setting up The apparatus, including the mass of the jaws, shall be balanced before the specimen is mounted. Mount the test specimen centrally
42、in the jaws with the jaws parallel. Where appropriate, do this by having the outer two lines, which were previously drawn 200 mm apart across the width of the specimen, positioned as close as possible adjacent to the inside edges of the upper and lower jaw. Take care that the specimen length in the
43、machine direction is parallel to the direction of application of force. Attach the apparatus for measuring strain. 8.2 Application of pre-tension Apply the pre-tension which includes any load due to the mass of the jaws. If possible, record the strain up to application of the pre-tension but do not
44、include it in the overall value of strain. 8.3 Measurement of dimensions Carry out measurements after application of the pre-tension. Determine the specimen width from the average of three measurements, each made at different positions in the gauge length of the mounted specimen with a resolution of
45、 0.5 mm. Determine the specimen width of a geogrid from the number of ribs under load multiplied by the average rib spacing as determined from three measurements at separate positions on the roll. Determine the gauge length from the average of two measurements between the inner two lines drawn on th
46、e specimen, to which is attached the extensometer clamps. Make measurements at opposite ends and sides of the specimen, to the nearest 0.5 mm. 8.4 Application of load Apply the load smoothly but rapidly to the specimen at a rate which will not cause any rebound. This may be checked either by monitor
47、ing strain or by a load cell mounted in series with the end of the specimen. The loading time excluding any pre-tension shall be between 2 s and 60 s and shall be recorded. NOTE 1Particular attention should be paid to adjusting the mechanism to maintain levers within their calibrated limits (see 5.1
48、) and to avoiding any undue load on or distortion of the specimen when making such adjustments. NOTE 2Starting time is the moment at which the full load is first applied to the specimen. With certain jaws such as roller grips the specimen will slip during loading. If this slippage is seen to be unev
49、en across the width of the specimen, for example by curvature of one of the outer two lines, abandon the test. Licensed Copy: sheffieldun sheffieldun, na, Wed Dec 06 12:56:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 6906-5:1991 BSI 02-19993 8.5 Measurement of strain Measure strain and time continuously, or at intervals as given below, after the load is applied. Record the time of loading. After an elapse of 10 the period of loading, take not less than the following number of measurements: four within the first 0.1 h; four more within the