Designation: d 2434 – 68 (Reapproved 2006) Standard Test Method for Permeability of Granular Soils
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- 8. Calculation
| 7. Procedure
7.1 Open the inlet valve from the filter tank slightly for the first run to conditions described in 3.1.3 , delay measurements of quantity of flow and heat until a stable head condition without appreciable drift in water manometer levels is attained. Measure and record the time, t, head, h (the difference in level in the manometers), quantity of flow, Q, and water temperature, T. 7.2 Repeat test runs at heads increasing by 0.5 cm in order to establish accurately the region of laminar flow with velocity, v (where v = Q/At), directly proportional to hydraulic gradient, i (where i = h/L). When departures from the linear relation become apparent, indicating the initiation of turbulent flow conditions, 1-cm intervals of head may be used to carry the test run sufficiently along in the region of turbulent flow to define this region if it is significant for field conditions. N OTE 5—Much lower values of hydraulic gradient, h/L, are required than generally recognized, in order to ensure laminar flow conditions. The following values are suggested: loose compactness ratings, h/L from 0.2 to 0.3, and dense compactness ratings, h/L from 0.3 to 0.5, the lower values of h/L applying to coarser soils and the higher values to finer soils. 7.3 At the completion of the permeability test, drain the specimen and inspect it to establish whether it was essentially homogeneous and isotropic in character. Any light and dark alternating horizontal streaks or layers are evidence of segre- gation of fines. 8. Calculation 8.1 Calculate the coefficient of permeability, k, as follows: k 5 QL/Ath where: k = coefficient of permeability, Q = quantity of water discharged, L = distance between manometers, A = cross-sectional area of specimen, t = total time of discharge, h = difference in head on manometers. 8.2 Correct the permeability to that for 20°C (68°F) by multiplying k (see 8.1 ) by the ratio of the viscosity of water at test temperature to the viscosity of water at 20°C (68°F). 9. Report 9.1 The report of permeability test shall include the follow- ing information: 9.1.1 Project, dates, sample number, location, depth, and any other pertinent information, 9.1.2 Grain size analysis, classification, maximum particle size, and percentage of any oversize material not used, 9.1.3 Dry unit weight, void ratio, relative density as placed, and maximum and minimum densities, 9.1.4 A statement of any departures from these test condi- tions, so the results can be evaluated and used, 9.1.5 Complete test data, as indicated in the laboratory form for test data (see Fig. 3 ), and 9.1.6 Test curves plotting velocity, Q/At, versus hydraulic gradient, h/L, covering the ranges of soil identifications and of relative densities. tải về 126.61 Kb. Chia sẻ với bạn bè của bạn:
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