AS 1289.3.6.3:2020 – Methods of testing soils forengineering purposes Part 3.6.3: Soil classification tests-Determination of the particle size distribution of a soil-Standard method of fine analysis using a hydrometer.
7.4 Preparation for sedimentation The procedure shall be as follows:
(a) Transfer the liquid to the stirring devIce cup and operate for 15 mm. lithe volume of liquid exceeds the capacity of the cup, this process will need to be completed in multiple steps as follows:
(i) Transferthe mixture to the high-speed mechanical stirrer or to the air-,et dispersion cup. using a et of distilled water.
(ii) Transfer the suspension that has passed through the sieve to the 1 L measuring cylinder and make up to exactly 1 L with distilled water This makes the suspension to be used In the sedimentation analysis.
(b) For soils likely to suffer severe structural breakdown, it is recommended that the air dispersion device be used, and mechanical dispersion not be used before washing over the 75 pm sieve.
(c) In the case of (a) or (b) operate the dispersion device for 15 mm. When using the mechanical stirrer use the baffle in the mechanical stirrer container. When using the air-jet dispersion device, operate It at a gauge pressure of 140 kPa ± 10 kPa.
7.5 SedimentatIon
The procedure shall be as follows:
(a) Place the I L cylinder contalmng the susenson n the constailt teinper-ature room, or batn and preferably leave it to stand until it has attained the ambient temperature of 20 C * I C. Close the mouth of the cylinder with the palm of the hand, or with a suitable watertight stopper or lid, and turn the cylinder end over end thoroughly for about 60 rotations In 1 mm.
(b) Immediately after shaking, place the cylinder on a firm, level and vibration-free place in the constant temperature room or bath. Then proceed as follows:
(I) Start the stop-clock and record the time of commencement of the test.
(ii) Immediately immerse the hydrometer to a depth slightly below its floating position and allow it to float freely.
(iii) Take readings at the top of the meniscus at 0.5-, 1-, 2-, and 4-mm intervals and record readings to the nearest gram per litre (or 0.0005 g/mL) (Rh).
(iv) Remove the hydrometer slowly, rinse it in distilled water, and place it in another cylinder of distilled water, which Is at the same temperature as that of the suspension.
v) Re-insert the hydrometer in the suspension and take readings at elapsed times of B, 15 and 30 mm and 1.2,4 and 8 hrs.
(vi) Remove the hydrometer after each reading, rinse it, and replace it in the cylinder of distilled water.
(vii) After the 4 h reading take further readings once or twice daily up to 48 h after dispersion, recording the times of reading. (Always insert and withdraw the hydrometer carefully when taking a reading to avoid undue disturbance of the suspension, allowing 10 s for each operation. Avoid vibration of the sample from any source.)
(c) Record the temperature of the suspension once during the first 15 mm of sedimentation and then after every subsequent reading. Record the temperature, accurate to within ±0.5 °C (see Clause 10 Note 7).
(d) At the conclusion of the sedimentation test —
(I) transfer the contents of the cylinder after decantation to an evaporating dish (mass determined to within 0.01 g);
(ii) dry in the oven at 105°C to 110 °C;
(iii) cool in the desiccatorand determine the mass of thecontents to the nearest 0.01 g; and (iv) record the mass as the mass of the fraction passing the 75 pm sieve (m6u)
uncorrected for dispersing agent.
(e) For soils which do not require pre-treatment. or where the mass 01 material in suspension at the commencement of the hydrometer analysis has been found in the course of its preparation during fine sieve analysis (refer to AS 1289.3.6.1), omit the drying of the material after hydrometer analysis.
For soils which did require pre•treatmcnt. obtain the mass of the fraction passing the 75 pm sieve (m6) from the difference between the calculated oven-dry mass (m4) of the subsample obtained in Clause 7.1(a) and the oven-dry mass (m5) of the fraction of the sample retained on the 75 pm sieve.