Lab 6. Constant Head and Falling Head Permeability Test in Sand (Lab13 and Lab14 in 9-5, Lab 10 in 8) * The rate of flow of water through a soil specimen of cross-sectional area A can be determined as q=kiA where q = flow in unit time, k=coefficient of permeability, i= hydraulic gradient k is defined as a measure of material's capacity to transmit water * k can be determined in the lab by * Constant head test (for coarse grain) * Falling head test (for coarse or fine grain soils) வாடா q=kiA QL hAt h then k = 9 he iA due to q = Q/t and i=h/L out Flow OUTFLOW Figure 3 Sketch of the combination permeameter test: Falling head (left), constant head (right) Falling Head Test Constant Head Test Allow water flowing through the sample Measure Q flowing through the sample and measure the time (t) to drop from over a period of time (t) under a steady the upper (h.) to the lower head (h) state head condition (h) Water supply Overflow pipe Funnel Plastic tube * Assembly a permeameter * Bottom porous stone * 2/3 of compacted sandy soil Top porous stone * Spring * Fix the specimen tube Stopper Spring Porous stone Plastic cylinder Porous stele Scales Stand Stopper Constant head chamber Figure 10-1. Schematic diagram of constant head permeability test setup * Data Recording for constant head * Use data sheet for Constant-Head Permeability Test : Determination of Coefficient of Permeability in p.309 (95) Determine Q three times with the same collection time and the same head difference h. Then find the average value of Q and record it. Data Recording for falling head * Use data sheet for Falling-Head Permeability Test : Determination of Coefficient of Permeability in p.309. * Take a reading Vw from burette * Read h, and h, from ruler * Record time t from hi to h2 * Calculation * Ignore Table 13-4 and 14-1 determination of void ratio of specimen * Calculate k and k20-c for constant-head method * k= QL 7200 Aht k20°c = kopec * Calculate k and k20-c for falling-head method 2.303VWL hi ητο log k20°c = krec (h1 - h2)ta h2 720°C k = * Lab Report (see section 13.7 and 14.7 in your textbook) - Results section should include data tables and sample calculations for both permeability tests. - Discuss the variation of k between two test methods. - Discuss any sources of error 2 1 uoo E 460 ulo ulo 430 490 510 6oo Soo 513.3 483.3 Constant-Head Permeability Test Determination of Coefficient of Permeability = =406.6 Description of soil Sample no Location Tested by Date Test No. 3 23.3 Item 2 xxxx Average flow, Q (cm) Repeat 3x record Avg 406d 513,3 483.3 Time of collection, 1 (s) 60 60 60 Temperature of water, T(°C) 18.5 19.5 20 Head difference, h (cm) 833 178.3 73.3 Diameter of specimen, D (cm) 7.5 7.5 7.5 Length of specimen, L (cm) 12.5 12.5 12.5 Area of specimen, A =D2 (cm) 5. 73.3 QL k= Aht (cm/s) Average k= cm/s Temperature of water °C ngoc С K20 c =krc 720°C cm/s copyright Oxford University Press Use approx. 600-700g of material. Falling-Head Permeability Test Determination of Coefficient of Permeability Description of soil Sample no. Location Tested by Date Test No. Item 1 2. 3 7.5 125 Diameter of specimen, D (cm) 17.5 7.5 Length of specimen, L (cm) 12.5 112.5 Area of specimen, A (cm) Beginning head difference, hi (cm) 63.5 hebt 75 Ending head difference, h2 (cm) 575 Test duration, 1 (s) 14.82 6.49 Volume of water flow through specimen, Vw (cm) 20 45 175 57.5 llo 9.89 28 2.303V L hi k= log (cm/s) (hi - h2)A h2 Average k = cm/s Temperature of water Пrc K20 c =kroc cm/s 120°c copyright Oxford University Press 95 70
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