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Standard Test Method for Permeability of Granular Soils (Constant Head) D 2434-68 “Abstracted, with permission, from the 1996 Annual Book of ASTM Standards, copyright American Society for Testing and Materials, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959” SCOPE This test method covers the determination of the coefficient of permeability, by constant head method for the laminar flow of water, through granular soils. The procedure is to establish representative values of the coefficient of permeability of granular soils that may occur in natural deposits as placed in embankments, or when used as base coarse under pavements. In order to limit consolidation influences during testing, this procedure is limited to disturbed granular soils containing not more than 10% soil passing the No. 200 (75 m) sieve. DEFINITION: “Permeability generally relates to the propensity of a soil to allow water to move through its void spaces.” Darcy’s Law: “The flow rate of water q through a soil of cross-sectional area A is directly proportional to the imposed gradient (slope) i” (q/A)~i q=kiA k = coefficient of permeability or permeability k is directly proportional to void ratio FUNDAMENTAL TEST CONDITIONS The following test conditions are prerequisites for laminar flow of water through granular soils, under constant-head conditions: 1. Continuity of flow with no soil volume change during a test. 2. Flow with the soil voids saturated with water and no air bubbles in the soil voids. 3. Flow is steady state with no change in hydraulic gradients. 4. Direct proportionality of velocity of flow with hydraulic gradients below certain values, at which turbulent flow starts. All other types of flow involving partial saturation of soil voids, turbulent flow, and unsteady state of flow are transient in character and yield variable and time-dependent coefficients of permeability; therefore, they require special test conditions and procedures. APPARATUS Permeameters – specimen cylinders with minimum diameter of 8 or 12 times the maximum particle size. The permeameter should be fitted with a porous disk at the bottom with permeability greater than that of the soil specimen, but with openings small enough to prevent movement of the soil particles. The permeameter should be fitted with manometer outlets for measuring head loss, h, over a length, 1, equivalent to at least the diameter of the cylinder. Manometer tubes with scales for measuring head of water. Large funnels Timing device Thermometer Vacuum pump or water-faucet aspirator Weight Balance SAMPLE A representative sample of air-dried granular soil containing less than 10% of the material passing the No. 200 sieve. PROCEDURE 1. Open the inlet value from the water tank slightly for the first test. Allow the water to flow through the sample until a stable head is established and there is no change in the manometer levels. 2. Measure and record the time, t, for a predetermined quantity of water, Q, to flow through the sample. 3. Measure and record the head, h (difference between the manometer readings). 4. Repeat the test with a different value of the head, h. Note: This test should be run at least five times. CALCULATIONS Calculate the coefficient of permeability, k as follows: QL k cm/s Ath Where: k = coefficient of permeability in cm/s 3 Q = quantity of water discharged in cm L = distance between manometers openings in cm t = total time to collect the quantity Q seconds h = difference in head on manometers in cm 2 A = cross-sectional area of specimen in cm 2 A = πD /4 where D = Inside diameter of the permeameter in cm Correct the permeability to that for 20o C (68oF) by multiplying k by the ratio of the viscosity of water at the test temperature to the viscosity of water at 20oC (68oF). kcorrected = k*correction factor Refer to Table 17-2 for correction factor value (Handout will be given for each group in class). PERMEABILITY DATA SHEET Date: _____________ Group: _________________ Distance between manometers, L: __________________ Inside diameter of the permeameter, D:_______________ Cross-sectional area of sample, A: _______________________ Test Manometer readings Head, Q (ml) t Q/At Hydraulic Tem K Correction K No. h1(cm) h2(cm) h=(h1-h2) (s) (cm/s) gradient perat (cm/s) Factor Corrected (cm) h/L ure cm/s o C REPORT Single page memorandum using MS Word: Letter format addressed to Dr. Julian Kang Subject of memo to have the experiment name Body of letter to contain 1. Objective of doing the experiment 2. Short paragraph description of how the experiment was done in lab (own words) 3. Results obtained from the experiment Data sheet Plot of fluid velocity Q/(A*t), versus the hydraulic gradient h/L. Value of corrected coefficient of permeability, k.
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