Geosynthetics. continued. Prof K. Rajagopal. IIT Madras, Chennai

Transcription

1 Testing of Geosynthetics continued Prof K. Rajagopal Department of Civil Engineering IIT Madras, Chennai in

2 Recap Earlier lectures have discussed the testing for the following properties of geotextiles Physical.. Fundamental material properties, p e.g. specific gravity, etc. Mechanical strength properties Hydraulic permeability properties Testing of Geosynthetics-3 2/36

3 Other Properties of Geotextiles Abrasion resistance Durability properties Melt flow index Asphalt retention Testing of Geosynthetics-3 3/36

4 Abrasion Resistance ASTM D1175 Abrasion is the wearing away of a part of the material due to rubbing against another surface Degradation in strength and material loss may happen due to continuous rubbing with rough and hard surfaces during service life of a geotextile. Abrasion is especially important in below railway track applications Rotary platform with a double head fitted with 1000 g vitrified abrasion wheels is used in this test. Geotextile is a disk shaped sample with 90 mm outer diameter and 60 mm inner diameter. After 1000 cycles of rotation, strip tensile strength tests are performed Abrasion resistance is expressed as the ratio of the tensile strength of the abraded sample with that of the virgin sample. Typical loss of tensile strength is about 40% after 1000 abrasion cycles. Loss in weight is also reported after the abrasion tests Testing of Geosynthetics-3 4/36

5 Abrasion by sand paper (ASTM D4886) The abrasion in this test is induced by rubbing a linear geotextile sample by a sand paper Loss in weight and tensile strength after 750 abrasion cycles is reported as the abrasion loss. Schematic of an abrasion testing device Testing of Geosynthetics-3 5/36

6 Durability tests on geotextiles Accelerated Durability Studies on Geotextiles Wetting of samples in seawater during nights Drying of samples in sun light during day time Testing of Geosynthetics-3 6/36

7 Results from alternate wetting and drying 350 WOVEN G/T(WHITE) GEOCOMPOSITE WOVEN G/T(BLACK) NON WOVEN TE ENSILE STRE ENGTH(kN/ /m) TIME (DAYS) No. of cycles Testing of Geosynthetics-3 7/36

8 Tests on paver or overlay fabrics Paver or overlay fabrics are used in surface treatment of pavements for protection of surface Prevents the propagation of cracks from old pavement section to the new overlay section Testing of Geosynthetics-3 8/36

9 Use of overlay fabrics for protecting pavements Testing of Geosynthetics-3 9/36

10 Pavement surface with overlay fabric Typical alligator cracks on the pavement surface Pavement surface without overlay fabric Performance of asphalt pavements with and without overlay fabrics Testing of Geosynthetics-3 10/36

11 Cyclic load tests to study the propagation of reflected cracks Testing of Geosynthetics-3 11/36

12 Typical results from laboratory tests on influence of geosynthetic layeron reflection cracking (Khodaii et al. 2009) Testing of Geosynthetics-3 12/36

13 Melting point of paving fabrics o When geosynthetics are used in flexible pavements they come in contact with hot asphalt during construction. o Geotextiles should not undergo structural changes due to exposure to excessive heat during construction. o The temperature at which the fibres melt can be determined from this test. o Differential Scanning Calorimeter (DSC) can be used to determine the melting point of the polymer as thermal transition point. Testing of Geosynthetics-3 13/36

14 Asphalt retention of paving fabrics (ASTM D6140) This test determines how well the geotextile can bond with asphalt Geotextile samples of mm size are taken They are submerged in bitumen at C for 30 minutes The saturated specimens are hung in the same oven at the same temperature for 30 minutes from one end and for another 30 minutes from another end Then the test specimens are cooled for 30 minutes and weighed to the nearest 0.1g. Asphalt retention = (W sat W o ) /A g where W sat is the saturated weight of the sample (g), W o is original weight of the sample (g) and A g is the area of the sample in m 2. Testing of Geosynthetics-3 14/36

15 Tests on Geogrids Aperture opening & Percent Open Area Thickness of rib and juctions Number of ribs per meter length Mass per Unit Area Tensile strength Interface frictional strength Shear pullout Connection strength between facing blocks and geogrids Testing of Geosynthetics-3 15/36

16 Biaxial composite geogrid nodes Aperture opening sizes bars nodes ribs Testing of Geosynthetics-3 16/36

17 Uniaxial geogrid transverse bars ribs Elongated apertures with very long ribs and short bars Testing of Geosynthetics-3 17/36

18 Thickness & No. of ribs and bars per unit length Thickness of bars Thickness of ribs Thickness of nodes Count the no. of ribs and bars per metre length by spreading the geogrid on a flat surface Testing of Geosynthetics-3 18/36

19 Percent Open Area Samples of at least 200 mm 250 mm representative of the geogrid are cut from the roll The geogrid pattern is drawn on a piece of paper Weigh the paper with the grid pattern accurate to g Cut out the grid opening areas from the paper Weigh the cut out portions Percent Open Area is the ratio of the weight of the cut out portions to the total weight of the paper multiplied by 100. Testing of Geosynthetics-3 19/36

20 Mass per Unit area Same procedure as used for geotextiles is applicable for the Mass per Unit Area of the geogrids also. The value is expressed in units of g/m 2. Testing of Geosynthetics-3 20/36

21 Tensile Strength of Geogrids ASTM D4595 (minimum width of 200 mm and gauge length of 100 mm, etc.) ASTM D6637 (single rib or multi ribs) Loading of samples at strain rate of 10 3% strain per minute Load at different deformations is measured to plot a graph between the strain on x axis and load/m on y axis Testing of Geosynthetics-3 21/36

22 ASTM D6637 Three junctions or 300 mm length Method da using single rib testingti Testing of Geosynthetics-3 22/36

23 Three junctions or 300 mm length Method-B using multi-ribs testing Testing of Geosynthetics-3 23/36

24 extensometer Gauge length for strains Fixed clamps Roller clamps Testing of Geosynthetics-3 24/36

25 Different types of grips Spacer block Roller grips Special grips used for testing extruded geogrids grid is held in position due to the elongated nodes width of the spacer blocks is changed for different geogrids Trapezoidal grips Testing of Geosynthetics-3 25/36

26 Tensile Strength Test of a knitted geogrid using roller clamps as per Method-A single rib test - geotextile padding given at supports to promote rupturewithin the gauge length Testing of Geosynthetics-3 26/36

27 Tensile strength Tensile strength of geogrid per meter width = Peak tensile load x No. of ribs per meter width/no. of ribs in the test Testing of Geosynthetics-3 27/36

28 Installation Damage of Geogrids (ASTM D 5818) Geogrids undergo damage during the construction The amount of damage depends on the type of aggregate, level of compaction, type of compaction equipment and construction practices The installation damage factor is specified after extensile field tests for site specific conditions ASTM 5818 recommends that the results from at least 20 tests should be used to determine the installation damage factor Typical damage factors are: for use in gravel/aggregate=1.1 1 to 1.2 for use in fine soils 1.05 to 1.1 for railway track applications, the damage factor could be much higher because of the large angular particles Testing of Geosynthetics-3 28/36

29 Field tests to determine the installation damage factor Testing of Geosynthetics-3 29/36

30 Field tests to determine the installation damage factor Testing of Geosynthetics-3 30/36

31 Tests on Geonets & Other drainage Products Geonets are predominantly used for erosion control works or for drainage purposes The in plane permeability of the geonets is evaluated using the procedure as applicable to geotextiles The normal pressures should correspond to the expected normal pressures in the construction Testing of Geosynthetics-3 31/36

32 Tests on Geomembranes Thickness Density Tensile strength/elongation g Permeability Peel tests on seams Shear tests on seams Testing of Geosynthetics-3 32/36

33 Thickness of a Geomembrane (ASTM D5199) Size of geomembrane sample is minimum 75 mm diameter Applied pressure is 20 kpa on a footer plate of diameter 6.35 mm For thick or stiff geomembranes, higher pressures as much as 200 kpa may be used For textured geomembranes, the thickness is measured between the projections Testing of Geosynthetics-3 33/36

34 Density of Geomembranes (ASTM D792) Density of geomembranes is determined as applicable for plastic materials using weights to sink them in water as per ASTM D792. Testing of Geosynthetics-3 34/36

35 double welded seam Direction of loads for the shear strength of a seam seam Direction of loads for the peel strength of a seam Determining the Shear and Peel strengths of a seam Testing of Geosynthetics-3 35/36

36 Tensile strength and elongation at break of geomembranes (ASTM D638) Geomembranes are subject to severe strains during their service life due to heat from the atmosphere and also the heat produced by the decay of waste products in landfills They should be able to elongate to more than 500% without rupturing Dumbbell shaped are cut from geomembrane sheets using sharp dies Testing of Geosynthetics-3 36/36

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