BS ISO 18325:2015 pdf download – Geosynthetics — Test method for the determination of water discharge capacity for prefabricated vertical drains
As the temperature correction (see Annex A) relates only to laminar flow, it is advisable to work at temperatures as close as possible to 20 °C to minimize inaccuracies associated with inappropriate correction factors, should the flow be non-laminar.
NOTE The biological activity in the water is the one of facts for air bubbles, which will affect the index discharge capacity in a negative way. Some biocides have been shown to reduce the biological activity. Demineralized water of grade 2 according to ISO 3696 can also be used to prevent this risk of biological activity.
5.4 Pressure controller The pressure controller shall be provided for controlling the pressure of (10 ~ 300) kPa applied to the mounted specimen to an accuracy of ± 5 %. It shall be capable of maintaining the proposed pressure on the PVDs without any deformation which would influence the test results.
5.5 Equipment for determining the amount of water When the amount of water is determined by measurements of volume, a measuring vessel for determining the volume to an accuracy of 1 % is required. When the volume is determined by weighing, it shall be determined to an accuracy of 1 %.
5.6 Dissolved-oxygen meter, or apparatus in accordance with ISO 5813. 5.7 Stopwatch, for measuring time to an accuracy of 0,1 s.
5.8 Thermometer, to determine the water temperature used for the flow measurements to an accuracy of 0,2 °C.
6 Test specimens
6.1 Handling The sample shall not be folded and shall be handled as infrequently as possible to avoid disturbance to its structure. The sample shall be kept in a flat position without any load.
6.2 Selection Take specimens from the sample in accordance with ISO 9862. 6.3 Number and dimensions Cut three test specimens from the sample with the length parallel to the machine direction. The full width of the product shall be tested.
6.4 Specimen condition The specimens shall be clean, free from surface deposits and without visible damage or folding marks.
7 Test procedure
7.1 Cut the test specimens from the sample exposed to a temperature of (20 ± 2) °C for 24 h. The specimens shall be longer than the confined length. The geotextile portion that is unexposed to the pressure should be cut to ensure smooth entry and exit of water flow through the specimen.
7.2 Place the specimens under water containing a wetting agent at laboratory temperature, gently stir to remove air bubbles and leave to saturate for at least 12 h. Use an aryl alkyl sodium sulfonate at a concentration of 0,1 % by volume as the wetting agent.
7.3 For specimen installation in straight condition, use the procedure described in 7.3.1 and 7.3.2.
7.3.1 Wrap the specimen with flexible membrane except top and bottom parts. Place the specimen in the pressure cell and insert it into the slots. The specimen shall be mounted in a straight line.
7.3.2 Cover the top and bottom parts of specimen with flexible membrane so as to ensure no wrinkles are formed. See that the membrane wrapped to the specimen is watertight without leakage. The confined length of the PVD exposed to pressure shall be (300 ± 10) mm for tests in straight condition.
7.4 For specimen installation in buckled condition, use the procedure described in 7.4.1 to 7.4.4.
7.4.1 Fix the guide frames to the supporters in the pressure cell. Insert two fixing pins into the holes and tie them to a value of A of (60 ± 1) mm in guide frames. Insert the central pin into the slit and place to the left end.
7.4.2 Wrap the specimen with flexible membrane except top and bottom parts. Place the specimen behind the fixing pins and in front of the central pin of guide frames in the pressure cell and insert it into the slots (see Figure 2). Move the centre of specimen at a constant speed of (120 ± 10) mm/min using the central pin until B becomes 55 mm (using the pushing rod with rotating handle). Insert the central pin in the guide frame.
7.4.3 Cover the top and bottom parts of specimen with flexible membrane so as to ensure no wrinkles are formed. Check that the membrane wrapped to the specimen is watertight without leakage.
7.4.4 Measure the confined length of the buckled specimen using a metal ruler.
7.5 Put a pressure on the cell of 50 kPa and check if the cell and the flexible membrane are watertight.
7.6 Allow water to flow through the specimen in order to remove air at a hydraulic gradient smaller than 1,0 before each measurement of the amount of water. 7.7 When pressurized, a sudden increase in pressure may cause damage to the surface of the flexible membrane. Therefore, pressure shall preferably be increased by 50 kPa up to the specified pressure in 2 min. The applied pressures are 200 kPa for straight condition and 120 kPa for buckled condition to be consistent with EN 15237. The variation of pressure during the desired measurement period shall be less than 5 %.