Determination of grain size analysis by hydrometer test

SOIL MECHANICS LAB

1. DETERMINATION OF GRAIN SIZE ANALYSIS BY HYDROMETER TEST EXPERIMENT NO. 4 SOIL MECHANICS LABORATORY CE PC 594

2. SEDIMENTATION ANALYSIS It is useful for determining the grain size distribution of fine grained soils by using pipette test and hydrometer test. It describes the process of fine particles falling through a fluid, and is used to separate the particles by size in space and time. This analysis is based on Stoke’s law.

3. STOKE’S LAW This law provides a governing equation based on the hydrodynamics of a single spherical particle falling in stationary fluid. It states that, When a spherical particle falls through infinitely large medium of fluid, then it achieve constant terminal velocity, also called as settling velocity.

4. STOKE’S LAW The particle is driven downward by gravitational forces and retarded by drag forces and buoyant forces. A particle will accelerate downward in the fluid until the summation of drag forces and buoyant forces equal the gravitational force. Once these forces are in equilibrium the particle will achieve terminal velocity ( v S ). W F B F D F D

5. STOKE’S LAW W = F B + F D Where, W = Weight of particle, F B = Buoyant force, F D = Drag force) W= = ( Spherical particle) F B = = ; F B = Then, = (as =1) D= Dia of particle, = dynamic viscosity of fluid   W F B F D F D

6. ASSUMPTIONS OF STOKE’S LAW Particles must be spherical and smooth There is no interference between particles, no side wall effects. All particles have to be of same quantity. Settling of particles should be discrete particle settling Diameter of soil grains should be in between 0.2 mm and 0.0002 mm.

7. APPARATUS Hydrometer conforming IS:3104-1965 Two measuring cylinders of 1000 ml capacity Thermometers 75 micron sieve Balance accurate to 0.001 g Stop watch Wash bottles containing distilled water Reagent ( Sodium hexa metaphosphate and sodium carbonate)

8. APPARATUS HYDROMETER Measuring Cylinder

9. hydrometer It is a device which is used to measure density of soil suspension in gm/ml or gm/cc at he chosen depth at chosen time. It directly gives specific gravity of solid. Hydrometer have two parts, stem and bulb. Volume of hydrometer is almost equal to volume of bulb. Reading on hydrometer increases in downward direction. R h = ( -1) 1000 = (G s -1) 1000 Where , is in gm/cc.   h Stem Bulb H Neck

10. hydrometer

11. CORRECTIONS OF HYDROMETER READING There is three types of corrections is necessary while taking the reading R h . Meniscus correction (C m ) Temperature Correction (C T ) Dispersion agent correction (C D )

12. MINISCUS CORRECTION (C m ) Reading in stem should be taken at the lower level of meniscus. However due to presence of turbidity in soil suspension, it is opaque in nature. As a result of which upper level of meniscus is being read instead of lower level. Since, the hydrometer reading increases downwards, the meniscus correction should be positive.

13. TEMPERATURE CORRECTION ( C T ) Calibration of hydrometer is done at 27°C. Hence if the temperature during the performance of test is more than 27 ° C, it results in lower reading (lower density) is being observed. Hence temperature correction is positive. Case A- If T>27°C , R hcorrection =R h +C T Case B- If T<27 ° C , R hcorrection =R h –C T The temperature shall be read with an, accuracy of at least of 0.5%.

14. DISPERSING AGENT CORRECTION ( C D ) Addition of dispersing agent in the soil suspension increases its apparent density, which results in higher value of reading (lower level). Hence, correction applied in negative. COMPOSITE CORRECTION (C) C = C m ± C T – C D R hcorrected = R h + C

15. TEST PROCEDURE Determination of volume of the hydrometer bulb ( V h ): Pour about 800 ml of water in the 1000 ml measuring cylinder and note the reading at the water level. Immerse the hydrometer in water and note the water reading. The difference between the two readings is recorded as the volume of the Hydrometer bulb plus the volume of that part of the stem which is submerged. For practical purpose the error due to the inclusion of this stem volume may be neglected. Alternatively , weigh the hydrometer to the nearest 0.1g. This mass in grams is recorded as the volume of the hydrometer in ml. This includes the volume of the bulb plus the volume of the stem. CALIBRATION OF HYDROMETER

16. TEST PROCEDURE CALIBRATION OF HYDROMETER

17. TEST PROCEDURE In order to find the area of cross-section (A) of the measuring cylinder in which the hydrometer is be used, measure the distance, in cm, between two graduations of the cylinder. The cross-sectional area (A) is then equal to the volume included between the two graduations divided by the distance between them. Measure the distance (h) from the neck to the bottom of the bulb, and record it as the height of the bulb. The distance from the neck of the bulb to the nearest calibration mark (H) shall be measured and recorded. With the help of an accurate scale, measure the height between the neck of the hydrometer to each of the other major calibration marks (R h ). CALIBRATION OF HYDROMETER

18. TEST PROCEDURE Calibrating the hydrometer with the measuring cylinder for determining effective depth (H e ) corresponding to hydrometer reading. According to IS 2720 recommendation, 33 gm of sodium hexa meta phosphate (deflocculating agent) and 7 gm of sodium carbonate are mixed in 1 liter of distilled water for the preparation of dispersing agent. Filling the measuring cylinder up to 1000 ml with 900 ml of distilled water including 100 ml of dispersing agent solution. Then hydrometer is inserted and the top meniscus and bottom meniscus reading on the stem is noted down. The difference between the top and the bottom meniscus readings give the meniscus correction (C m ), which is positive . SEDIMENTATION TEST BY HYDROMETER

19. TEST PROCEDURE 50 gm oven dried soil sample passing 75 micron sieve is taken in a dispersion cup and 100 ml of dispersing agent solution is added. Then the mixture is stirred for about 15 minutes using a high speed stirrer. The soil suspension is transferred completely to the measuring cylinder. The measuring cylinder is filled by adding distilled water to increase the volume up to the 1000 ml mark. The measuring cylinder is then shake using palm of one hand on open end of the cylinder, turning the cylinder up side down and back for a number of times. After shaking, placed the cylinder on a levelled surface and a stopwatch is started simultaneously. SEDIMENTATION TEST BY HYDROMETER

20. TEST PROCEDURE Immediately the hydrometer is inserted carefully and the top meniscus reading at ¼, ½, 1 and 2 minute intervals. The hydrometer is removed and floated it in another cylinder containing distilled water. Then it is rinsed by a twisting motion to remove any soil particles that may have adhered on it. For any subsequent reading, the hydrometer is re- inserted just before reading. Further readings are taken after periods of 4, 8, 15 and 30 minutes and again after 1, 2 and 4 hours. After the end of 4 hours, readings are taken twice within 24 hours and the final reading is recorded at the end of 24 hours. SEDIMENTATION TEST BY HYDROMETER

21. TEST PROCEDURE The temperature of the suspension once during the first 15 minutes is recorded and then after every reading is taken. Hydrometer readings shall also be taken in pure distilled water at the corresponding temperatures and the temperature correction ( C T ) calculated as the difference between this reading and the reading corresponding to the density of water at the calibration temperatures. SEDIMENTATION TEST BY HYDROMETER

22. GENERAL INFORMATION We will use such information for hydrometer test V h = Volume of bulb in ml = 90 cc A = Cross sectional area of the cylinder = 29.85 cm 2 C m = Meniscus Correction = 0.0005 C d = Dispersion agent correction = 0.0035

23. CALCULATION The effective depth He corresponding to any hydrometer reading R h is given by, H e = H + (h- Hydrometer reading (R h ) is determined a t different time intervals t (in minutes). Plot graph between H and H e . Plot another graph between R h and H e . µ value should be take from chart for each reading. Determination of D; D = K ; Where, K = Where, H e = Effective depth in cm, t = time in minutes, = Viscosity in poise, g = 981 cm/sec 2 , G s = Specific gravity of soil, G w = Specific gravity of water= 1 under normal temperature conditions  

24. CALCULATION Calculation of corrected hydrometer reading R c = { ( R h + C m ± C T - C D ) -1}× 1000 Determination of N using formula Percentage finer = N(%) = where, M s = Mass of dry soil in gm The diameter of the particle in suspension at any time is calculated using equation by taking the value of H e from the calibration curve for reading R h . Plot the graph between dia of particle (in mm) in log scale and % finer N  

25. Table for C T and µ

26. CALCULATION table

27. CALCULATION table

28. CALCULATION table

29. GRAIN SIZE DISTRIBUTION CURVE

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