STRUCTURE OF THIS PRESENTATION - ISC’5 OF THIS PRESENTATION • Overview • Objectives of this research • Experimental details • Results and discussions • Conclusions 5th

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.


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.


Dispersing agents & Various methods worldwide


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.


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%.


Materials Used

• Dispersing agents:

a. Calgon

b. Sodium pyrophosphate

c. Sodium tetra pyrophosphate

• Hydrometer:

a. Hydrometer 152H.


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.


Figure 1. Effect of dispersing agent types on hydrometer readings.


-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).


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.


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.


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

)


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.


0

2

4

6

8

10

0 20 40 60 80 100 120

Cla

y c

on

ten

t (%

)


NaTPP (3.6%)

NaTPP (5%)

NaTPP (6%)

NaTPP (7%)

Effect of dispersing agents on activities of some soil

samples


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.


2016

Acknowledgement

The travel to Australia to attend and present in this conference is partially

funded by National Research Foundation (NRF), South Africa.


2016

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STRUCTURE OF THIS PRESENTATION - ISC’5 OF THIS PRESENTATION • Overview • Objectives of this research • Experimental details • Results and discussions • Conclusions 5th