STRUCTURE OF THIS PRESENTATION
• Overview
• Objectives of this research
• Experimental details
• Results and discussions
• Conclusions
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Overview
• Particle size analysis is a method of separation of the mineral part ofthe soil into various size fractions and the determination of proportions ofthese fractions.
• Accurate determination of clay content is important as it is used todetermine the activity of soil, which in turn is used for design purposes.
• Differences in the laboratory results are still common and substantial(formally expressed by Jacobsz and Day, 2008), which reinforces theneed that the field data should be collected very carefully by thesurveyors.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Methods of Particle size analysis
• There are two methods:
a. Mechanical or Sieve analysis – Distribution of the coarser, large-sized particles.
b. Sedimentation or Hydrometer analysis – Distribution of finer particles.
• Hydrometer analysis is based on STOKE’s Law, according to which the velocity of free fall of
grains is directly proportional to the square of the particle’s diameter.
• To determine the particle size distribution accurately, the individual soil particles must be
dispersed. The finer particles have a tendency to form flocs and it is necessary to prevent floc
formation to obtain the grain diameter of individual grains and not the floc. Hence
Deflocculating agents are added to prevent floc formation of fine soil particles.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Dispersing agents & Various methods worldwide
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
S.No. Method Dispersing agent
1. TMH1 (1986) Sodium Silicate + Sodium Oxalate
2. SANS 3001 (2014) Sodium hexametaphosphate (4%)
3. ASTM D422-63 (1965) Sodium hexametaphosphate (4 %)
4. BS 1377 (1990) Calgon (33:7)
5. IS 2720 (1985) Calgon (33:7)
6. ISRIC (2002) Calgon (40:10)
7. Lambe (1951) Sodium hexametaphosphate (4 %)
• Some other dispersing agents also used in past are sodium pyrophosphate (Schuurman &
Goedewaagen, 1971), sodium tetra pyrophosphate (Yoo & Boyd, 1994) and disodium di hydrogen
pyrophosphate (formerly used by the Soils Testing Laboratory of Department of Water Affairs of South
Africa).
• As the dispersing agents prescribed by TMH1 (1986) do not yield the maximum clay percentage, so
some national laboratories in south Africa use different dispersing agents other than prescribed ones.
• But, it has been observed that due to this deviation in the dispersing agents and following TMH1 (1986)
guidelines resulted into inaccurately inflated results.
• Only two known methods (SANS 2014 and ISRIC 2002) make provision for a correction for the effect of
dispersing agent on the hydrometer readings.
• The hydrometer test readings should be corrected by subtracting the readings obtained on blank
solutions (only water and dispersing agent) from readings taken on the suspension solution.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Objectives
• The effect of various phosphate dispersing agents (calgon, sodium
pyrophosphate and sodium tetra pyrophosphate) and variation in their
concentration and volume on the hydrometer test readings were considered
while following TMH1 guidelines.
• Various concentrations of various dispersing agents used were as follows:
a. Calgon: 35:7 (4.2%), 40:10 (5%), 60:10 (7%), 70:10 (8%), 80:10 (9%) and
90:10 (10%).
b. Sodium Pyrophosphate: 3.6%, 5%, 6% and 7%.
c. Sodium Tetra Pyrophosphate: 3.6%, 5%, 6% and 7%.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Materials Used
• Dispersing agents:
a. Calgon
b. Sodium pyrophosphate
c. Sodium tetra pyrophosphate
• Hydrometer:
a. Hydrometer 152H.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Testing Procedure
• Testing was done while following TMH1 (1986) guidelines with various dispersing agents.
• For any soil sample, the percentages finer than 0.075 mm, 0.05 mm, 0.04 mm, 0.026 mm,
0.015 mm, 0.01 mm, 0.0074 mm, 0.0036 mm and 0.0015 mm were respectively calculated
by the readings taken at 18 sec, 40 sec, 2 min, 5 min, 15 min, 30 min, 1 hour, 4 hour and 24
hours respectively, by means of the following equation.
P = (c*sf)/sm
• Where, P = Percentage finer than relevant size, Sm = Mass of soil fines used in analysis, Sf =
Percentage soil fines in total sample (<0.425 mm), C = Corrected hydrometer reading.
• After the calculations, the calibration curve was plotted.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Figure 1. Effect of dispersing agent types on hydrometer readings.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
-1
0
1
2
3
4
5
6
0.001 0.01 0.1
Co
rrec
ted
Hyd
rom
eter
Rea
din
g
Grain Size (mm)
Water + Sod Silicate + Sod Oxalate
(Original TMH1)
Water + 125 ml of Calgon 4.2%
Water + 20 ml of Sod
Pyrophosphate Decahydrate 3.6%
Water + 20 ml of Sod Tetra
Pyrophosphate 3.6%
Figure 2. Hydrometer reading corrections for different grain sizes for Calgon (80:10).
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
5
10
15
20
25
30
35
40
45
50
55
0.001 0.01 0.1
Co
rrec
ted
Hyd
rom
eter
Rea
din
g
Grain Size (mm)
100 ml
125 ml
150 ml
175 ml
200 ml
225 ml
250 ml
275 ml
300 ml
325 ml
350ml
375ml
400ml
425ml
450ml
475 ml
Calgon 80:10
Figure 3. Effect of volume and concentration of Calgon on clay-sized period readings.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
0
5
10
15
20
25
30
35
40
45
50
75 100 125 150 175 200 225 250 275 300 325 350 375 400 425 450 475 500
Co
rrec
tio
n t
o C
lay S
ized
Hyd
rom
eter
Rea
din
gs
(g/l
itre
)
Volume of dispersing agent (ml)
Calgon (4.2%)
Calgon (5%)
Calgon (7%)
Calgon(8%)
Calgon (9%)
Calgon (10%)
Figure 4. Effect of volume and concentration of sodium pyrophosphate decahydrate on
clay-sized period readings.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
0
5
10
15
20
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340
Co
rrec
tio
n t
o C
lay S
ize
Hyd
rom
eter
Rea
din
gs
(g/l
itre
)
Volume of dispersing agent (ml)
NaPP (3.6%)
NaPP (5%)
NaPP (6%)
NaPP (7%)
Figure 4. Effect of volume and concentration of sodium tetra pyrophosphate on clay-sized
period readings.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
0
2
4
6
8
10
0 20 40 60 80 100 120
Cla
y c
on
ten
t (%
)
Volume of dispersing agent (ml)
NaTPP (3.6%)
NaTPP (5%)
NaTPP (6%)
NaTPP (7%)
Effect of dispersing agents on activities of some soil
samples
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September, 2016
Properties Light Yellow soil Black soil Light Brown Soil Red soil
Liquid Limit (LL) 32 56 33 28
Plastic Limit (PL) 16 22 24 15
Plasticity Index (PI) 16 34 9 13
% age clay content determined with DA correction (C)
21.5 32 5.7 29
Activity determined with DA correction (A)
0.74 1.06 1.58 0.45
% age clay content determined without DA correction (C’)
32.4 44 11.8 40
Activity determined without DA correction (A’)
0.49 0.77 0.766 0.33
∆ % Activity 33.8 27.4 51.9 26.7
Conclusions
The following conclusions were drawn from the study conducted:
• Tests with different dispersing agents clearly indicated that the hydrometer
readings of blank solutions varied significantly depending upon the type of
dispersing agent.
• The hydrometer readings for blank solutions increased with an increase in
the concentration and volume of a dispersing agent. For Calgon, the
hydrometer readings varied from 5 to 47 (g/litre) while for sodium
pyrophosphate decahydrate and sodium tetra pyrophosphate, they varied
from 0 to 20 (g/litre) and 0 to 9 (g/litre), respectively.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September,
2016
Conclusions
• The increase was attributed to the aggregation of uniformed sized solid
particles of dispersing agent in the hydrometer cylinder, increasing the
density of the solution in the zones measured by the hydrometer.
• There is an average decrease ranging from approximately 27 % to 52 %
(average of 36 %) in the activities of soils computed with the clay content
determined without dispersing agent corrections.
• Readings of hydrometer tests where deviations from the prescribed type,
volume, and concentration of the dispersing agent occur should be
appropriately corrected.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September,
2016
Acknowledgement
The travel to Australia to attend and present in this conference is partially
funded by National Research Foundation (NRF), South Africa.
5th International Conference on Geotechnical and Geophysical Site Characterisation, Gold Coast, Australia – 8th September,
2016