AASHTO R 74:16(2020) Standard Practice for Wet Preparation of Disturbed Soil Samples for Test.
This method describes the wet preparation of soil samples, as received from the field, for mechanical analysis and the determination of soil constants.
Method A provides for drying the field samples at a temperature not exceeding 60°C (140°F), making a wet separation on the 0.425-mm (No. 40) sieve and drying to a temperature not exceeding 60°C (140°F). Method B provides that the field sample shall be kept at a moisture content equal to or greater than the natural moisture content. Samples of such soil should be shipped to the laboratory in sealed containers and not allowed to dry out before testing. If no procedure is specified, Method A shall govern.
The values stated in SI units are to be regarded as the standard.
The soil sample as received from the field shall be dried thoroughly in air, in a warming oven whose temperature is not above 60°C (140°F), or by means of a device that will not raise the temperature of the samples above 60°C (140°F). The aggregations shall then be thoroughly broken up in the mortar with a rubber-covered pestle or suitable mechanical device in such a way as to avoid reducing the natural size of individual particles. A representative test sample of the amount required to perform the desired tests shall then be selected by the method of quartering or by the use of a sampler.
5.2. The portion of the air-dried sample selected for the purpose of mechanical analysis and physical tests shall be weighed and the mass recorded as the mass of the total sample uncorrected for hygroscopic moisture. The test sample shall then be separated into two portions by means of a 0.425-mm sieve. The material passing the 0.425-rnni sieve shall be set aside for later recombination with additional material as described in Sections 5.3 to 5.7.
5.3. The material retained on the 0.425-mm sieve shall be placed in a pan, covered with water, and allowed to soak for a period of 2 to 24 h until the particle aggregations have become soft and broken down.
5.4. After soaking, the material shall be washed on a 0.425-mm sieve in the following manner: The empty 0.425-mm sieve shall be set in the bottom of a pan and the liquid from the sample poured into it. Enough additional water shall be added to bring the level of the water in the pan approximately 13 mm (1/2 in.) above the mesh of the sieve. A portion of the soaked material not to exceed 0.45 kg (I Ib) in mass shall be placed in the water on the 0.425-mm sieve and stirred by hand at the same time the sieve is agitated up and down. If the material retained on the 0.425-mm sieve contains lumps that have not slaked or disintegrated, but which can bc crumbled or mashed between the thumb and finger so as to pass the 0.425-mm sieve, such lumps shall be broken and washed through the sieve into the pan. After all lumps have been broken up, the sieve shall be held above the soil and water in the pan and the material remaining on the sieve shall be washed with a small amount of clean water. The washed material retained on the 0.425-mm sieve shall be transferred to a clean pan.AASHTO R 74 pdf download.