Print Email Facebook Twitter Settling Tube Analysis of Sand Title Settling Tube Analysis of Sand Author Geldof, H.J. Slot, R.E. Faculty Civil Engineering and Geosciences Department Hydraulic Engineering Date 1979-06-01 Abstract For various reasons particle-size analysis of sediment is used in many fields of science and technology, a.o. earth sciences, agricultural and civil engineering. Relatively coarse-grained sediment like sand, with dimensions ranging from 0.06 till 2 mm, is analyzed almost exclusively by sieving. The size of particles in the silt and clay range (0.002 - 0.06 mm resp. smaller than 0.002 mm) commonly is derived from their settling velocity using Stokes' law; in this connection the important studies by Odén (1915, 1925) and Fisher/Odén (924) are recalled. Since the 1930's attempts have been made to remove this difference in analyzing technique by application of fall velocity analysis to sand-size sediment as well, using an empirical relation between size and fall velocity. A second and more important motive for the development of settling velocity analysis of sand is the surmise that the fall velocity of a particle might be a more fundamental property than its size as far as its behaviour in a stream is concerned. Hence, in studies on depositional environment of recent and ancient sediments settling velocity analysis is sometimes given preference to sieving (Reed et al., 1975; Emery, 1978). In this respect it is noted that in an alluvial stream the initiation of motion as well as the concentration distribution of suspended sediment with height are dependent on the ratio between shear velocity and fall velocity. Thirdly, in some cases the amount of material available to sampling is very small, e.g. in flume experiments on selective transport and in studies on sedimentary structures (Emery, 1978; Grace et al., 1978). Unlike sieving settling velocity analysis permits -- and sometimes necessitates the use of small samples. Fourthly, in settling velocity analysis the measurement process is continuous by nature. Therefore, more information is available than in the case of sieving, which is a discontinuous method. In addition, the application of a modern detection system and electronic data processing enables rapid analysis of a large number of samples in a short time. CONCLUSIONS 1. The specifications of the detection method applied in a settling tube are closely related to the characteristics of the sediment, the sedimentation fluid and the settling tube dimensions. 2. An underwater balance as applied in DUST is sufficiently accurate for fall velocity analysis of both fine and coarse sand. 3. Measurements in the test model of DUST have confirmed that the error due to settling convection is depending on particle size. For particles smaller than 0.2 mm the maximum value of the ratio between sample volume and settling tube volume, as estimated by the procedure of Kranenburg/Geldof (1974) is too large. 4. The reproducibility of the median fall velocity of samples of sieved sand, analyzed in the test model, is better than 2%. 5. Given a certain error in the measurement of the time of arrival of the particles at the level of measurement and given the maximum fall velocity in the samples to be analyzed, it can be shown that an optimum value of the delay time of the weighing system exists. The magnitude of the dynamic effect of the settling particles on the weighing system needs further study. Subject particle-sizeparticle-size analysissettling tubefalling velocitysandsedimentDUSTmeasurements To reference this document use: http://resolver.tudelft.nl/uuid:781aebaa-6816-43c0-b8ad-8478e5098410 Publisher TU Delft, Department of Hydraulic Engineering Source Report no. 4-79 Part of collection Institutional Repository Document type report Rights (c) 1979 TU Delft, Department of Hydraulic Engineering Files PDF Geldof_Slot1979.pdf 7.65 MB Close viewer /islandora/object/uuid:781aebaa-6816-43c0-b8ad-8478e5098410/datastream/OBJ/view