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Lab Report No, Exams of Law

University of Queensland (UQ)Law

Sedimentation analysis sorts soil particles by size using the physical ... Sedimentation test can be described by hydrometer analysis or pipette analysis.

Typology: Exams

2021/2022

Uploaded on 07/05/2022

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Lab. Report NO. 5
1
SEDIMENT A T ION ANA LYSIS
DEFINITION
Sedimentation (hydrometer and pipette) analysis defines the grain size
distribution curve of soils that are too fine to be tested with sieves.
Sedimentation analysis sorts soil particles by size using the physical
process that is described by (Stokes, 1891) when the particles are allowed
to settle under gravity.
INTRODUCTION
The theory of sedimentation is based on the fact that large particles in
suspension in a liquid settle more quickly than small particles, assuming
that all particles have similar densities and shapes.
Although clay particles are far from spherical, the application of Stokes’
Low based on diameters of equivalent spheres.
Sedimentation test can be described by hydrometer analysis or pipette
analysis.
A dispersing (also deflocculating) agent is used with a soil suspension in
water in order to ensure separation of discrete particles of soil. Two
materials are often used as dispersal agent to neutralize the soil- particle
charges:
1- Sodium hexa-metaphosphate (NaPO3) known commercially as
(Calgon) and for most purposes it has found that Calgon is one of
the most suitable and convenient dispersants.
2- Sodium silicate or water glass (Na2SiO3).
HYDROMETER ANALYSIS
DEFINITION
Hydrometer test is used to determine the grain size distribution of fine-
grained soils having particle size smaller than 0.075mm and if more than
10% of the soil passes the No.200 sieve. For soil samples have particle sizes
ranging from sand to silt or clay, sieving and sedimentation analysis are
combined.
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SEDIMENTATION ANALYSIS

DEFINITION

Sedimentation (hydrometer and pipette) analysis defines the grain size distribution curve of soils that are too fine to be tested with sieves. Sedimentation analysis sorts soil particles by size using the physical process that is described by (Stokes, 1891) when the particles are allowed to settle under gravity.

INTRODUCTION

 The theory of sedimentation is based on the fact that large particles in suspension in a liquid settle more quickly than small particles, assuming that all particles have similar densities and shapes.  Although clay particles are far from spherical, the application of Stokes’ Low based on diameters of equivalent spheres.  Sedimentation test can be described by hydrometer analysis or pipette analysis.  A dispersing (also deflocculating) agent is used with a soil suspension in water in order to ensure separation of discrete particles of soil. Two materials are often used as dispersal agent to neutralize the soil- particle charges: 1- Sodium hexa-metaphosphate (NaPO 3 ) known commercially as (Calgon) and for most purposes it has found that Calgon is one of the most suitable and convenient dispersants. 2- Sodium silicate or water glass (Na 2 SiO 3 ).

HYDROMETER ANALYSIS

DEFINITION

Hydrometer test is used to determine the grain size distribution of fine- grained soils having particle size smaller than 0.075mm and if more than 10% of the soil passes the No.200 sieve. For soil samples have particle sizes ranging from sand to silt or clay, sieving and sedimentation analysis are combined.

INTRODUCTION

 In many instances, the results of sieve analysis and hydrometer analysis for a given soil are combined on one graph.  The hydrometer is usually a type 152H (refer to Fig.1) and is calibrated to read grams of soil that still in suspension of a value of Gs=2.65 in1000 cm^3. For soils of other specific gravity a correction must be made. It gives the weight of particles located around the bulb centroid but not of those located above or below.

Fig (1)  Note that L is the depth measured from the surface of the water to the center of gravity of the hydrometer bulb at which the density of the suspension is measured.  It is intended that the specific gravity test be made on that portion of soil which passes the No.10 (2.00mm) sieve, when it is to be used in calculation in hydrometer analysis. CORRECTION OF HYDROMETER READING

The hydrometer readings are corrected as: i. Meniscus correction – Since the suspension is opaque, the observations are taken at the top of meniscus. The meniscus correction is equal to the reading between the top of the meniscus and the level of the liquid. As the

PROCEDURE

  1. Take exactly 50 g of oven dry (well pulverized soil), and mix with 125 ml quantity of 4% solution of sodium metaphosphate.
  2. Allow the mixture to stand about 1 hr. (ASTM suggest 16 hr for clayey soils). Transfer the mixture to the malt mixer cup and add distilled water until the cup is two thirds full, mix for 5 min.
  3. Transfers all the contents of the cup to the sedimentation cylinder (being careful not to lose any material). The volume of dispersed soil suspension is increased to 1000 ml by adding distilled water.
  4. Use the palm of your hand over the open end of the sedimentation cylinder and carefully agitate for about 1 min. (be sure no soil is stuck to the base of the cylinder). Set the cylinder down, immediately insert the hydrometer, and take hydrometer reading at elapsed time 0.5, 1, 2, 4 min also take temperature reading of sedimentation cylinder and control jar, then take meniscus correction and zero correction from the control jar.
  5. Repeat step 4 take another series of hydrometer readings at 0.5, 1, 2, 4min. of elapsed times. Repeat as necessary until two sets of the four reading agree within 1 unit of each other at all four reading time (take average between a pair of readings).
  6. Collect additional hydrometer and temperature readings at elapsed time of 8, 15, 30, min followed by 1, 2, 4, 8, 16, 24, 48, 96 hr.

CALCULATION

  1. Determine temperature correction (CT) from Table (6-3).
  2. Calculate corrected hydrometer reading (Rc) from following equation:

Rc = Ra – Zero correction + CT

  1. Determine (a) from Table (6-2) or from following equation:

a = ( GGx 11 ). x^652. 65

s

s

  1. Calculate %Finer of soil particles from following equation:

% Finer = ( RCWs^ x ( a )) x 100

  1. Calculate hydrometer reading (R )corrected for meniscus only by:

R = Ra + meniscus correction Ra = actual hydrometer reading from sedimentation cylinder.

  1. Determine effective depth (L) from Table (6-5) by using R.
  2. Determine K from Table (6-4) by using Gs and T.
  3. Calculate diameter (D in mm) of particles suspended in the cylinder at time t in minute by:

D = K Lt

Where: L in (cm), t in (min)

  1. Repeat all above steps for each hydrometer readings.
  2. Use the data from steps 4 & 8 above and plot the % Finer versus D in (mm).
  3. Find percent of silt and clay according to BS.
  4. Find coarse, medium and fine silt according to BS.

DISCUSSION

  1. Stokes law does not applied for colloids that are particles smaller than 0.0002 mm?
  2. Use the value of hydrometer reading (R) correction for meniscus only to find the value of (L)?
  3. What is the effect of the specific gravity (or density) decreases on the hydrometer reading?

2016