![]() The sum of the number of blows required for the second and third 6 in. The sample tube is driven 150 mm into the ground and then the number of blows needed for the tube to penetrate each 150 mm (6 in) up to a depth of 450 mm (18 in) is recorded. This is driven into the ground at the bottom of a borehole by blows from a slide hammer with a weight of 63.5 kg (140 lb) falling through a distance of 760 mm (30 in). Figure 2-31: The Standard Penetration Test (The test uses a thick-walled sample tube, with an outside diameter of 50 mm and an inside diameter of 35 mm, and a length of around 650 mm. The test procedure is described in the British Standard BS EN ISO 22476-3, ASTM D1586 and Australian Standards AS 1289.6.3.1. The standard penetration test (SPT) is an in-situ dynamic penetration test designed to provide information on the geotechnical engineering properties of soil. ASTM provides the detailed procedures for performing the Hydrometer test.Ĭlay particles can be sufficiently small that they never settle because they are kept in suspension by Brownian motion, in which case they may be classified as colloids. Stoke's law provides the theoretical basis to calculate the relationship between sedimentation velocity and particle size. Sand particles may take less than a second. Clay particles may take several hours to settle past the depth of measurement of the hydrometer. A hydrometer is used to measure the density of the suspension as a function of time. In the hydrometer tests, the soil particles are mixed with water and shaken to produce a dilute suspension in a glass cylinder, and then the cylinder is left to sit. If it is important to determine the grain size distribution of fine-grained soils, the hydrometer test may be performed. The classification of fine-grained soils, i.e., soils that are finer than sand, is determined primarily by their Atterberg limits, not by their grain size. Figure 2-30: A set of sieves (Essa Australia from: 2.6.2. According to the British standard, 0.063 mm is the boundary between sand and silt, and 2 mm is the boundary between sand and gravel. According to the Unified Soil Classification System, a #4 sieve (4 openings per inch) having 4.75mm opening size separates sand from gravel and a #200 sieve with an 0.075 mm opening separates sand from silt and clay. The boundary between sand and silt is arbitrary. If there are a lot of fines (silt and clay) present in the soil it may be necessary to run water through the sieves to wash the coarse particles and clods through.Ī variety of sieve sizes are available. Fine particles tend to stick to each other, and hence the sieving process is not an effective method. This method works reasonably well for particles in the sand and gravel size range. The stack of sieves is shaken for a standard period of time so that the particles are sorted into size bins. A known volume of dried soil, with clods broken down to individual particles, is put into the top of a stack of sieves arranged from coarse to fine. A stack of sieves with accurately dimensioned holes between a mesh of wires is used to separate the particles into size bins. The formal procedure is described in ASTM D6913-04(2009). ![]() ![]() The size distribution of gravel and sand particles are typically measured using sieve analysis. ![]()
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