soils lab notes

8/6/2019 Soils Lab Notes

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UNIVERSITY OF WESTERN SYDNEY

SCHOOL OF ENGINEERING

COLLEGE OF HEALTH SCIENCE

300720 CONSTRUCTION TECHNOLOGY 1 (Civil)

LAB 1 Notes Autumn 2011

Experiment 1: Soil Classification.

Soils, as we all know, can vary from gravels to stiff highly reactive clays. The type of soils has asignificant effect on buildings. Footings, which are appropriate for sandy soils, may result in severestructural cracking of the building if they are used in a soil zone with highly reactive clay.

It is important for a builder to correctly identify the type of soil at each building site. A series ofsimple tests can be requested from a geotechnical laboratory to classify a soil. The tests we willuse today determine the following properties:

1. Predominate grain size; clayey, sandy, gravelly etc

2. Grading; a measure of the range of particle sizes

3. Reactivity; through an indirect series of tests known as the Atterbergs Limits

Aim: To determine the engineering properties of a selected soil. The grading and plasticity of thesoil will be measured.

Part A Grading and Soil Type.

Introduction.

Grading refers to the distribution of particles in the soil.

A well-graded soil is defined as a material with a wide range of particle sizes. The smallerparticles (clay and silt) fit into the larger sand and gravel grains. Well-graded soils compact easilyand leave few air voids. The compacted soil tends to be dense and impermeable.

Poorly-graded soils tend to have a predominate particle size. Beach sand is an example of apoorly-graded material. They tend to drain quickly but conversely do not consolidate into a densemass.

Well-Graded Soil. Poorly-graded Soil.


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Figure 1: Well and poorly graded soils.

Grading and soil type are measured by mechanical sieving. Sieves are constructed with equalsized and shaped (usually square) openings. Grains of soil that is smaller than the size of theaperture will pass while larger grains are retained.

Obviously, a sieve can be used to separate soil grains in a sample into two groups; one containinggrains smaller than the size of the sieve opening and the other larger grains.

By passing the soil sample downward through a series of sieves each of decreasing sizeapertures, the soil grains can be separated into a number of groups, each of which contains grainswithin a particular size range.

Silt and clay fractions cannot be mechanically graded. Sieves with an aperture size less than 50microns (0.05 millimetres) are difficult to manufacture. Grain size analysis for these soils is doneby another method Hydrometer analysis or their distribution can be estimated from the sieveanalysis of larger fractions.

Equipment.

3 kg Electronic Balance 2 Off

A nest of sieves with pan and lid vis:--2.36 mm, 1.18 mm, 600 microns, 425 microns, 300 microns, 150 microns, 75 microns, 2 sets

Mechanical sieve shaker 2 Off

Soft whisk brush 2 Off

Methodology.

1. Load a sample of 300 g of soil onto the top most sieve 2.36 mm. Replace the lid and alertthe most available staff member. Do not take the nest of sieves yourself to the shaker.

2. Sieve the soil for 5 minutes through the complete nest of sieves; 2.36 mm, 1.18 mm, 600

microns, 425 microns, 300 microns, 150 microns, 75 microns. (1000 microns = 1millimetre)

3. Weigh the sample retained on each sieve and most importantly each empty sieve!!!


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Calculations.

1. Record the weight of the sample in each size range (i.e. 2.36 mm to 600 microns, etc) onTable 1. Sum the masses to find the total weight of sample.

2. Determine the cumulative percentage passing each sieve. The percentage for a particularsieve size is the total sample size LESS the soil retained by the sieve and the larger

aperture sieves above.i.e. for example; Cumulative % passing (600 microns sieve) =

100

600)18.1(36.2:

weightsampletotal

micronsmmmmweighteachweightsampletotal

And again Cum. % passing (425 microns sieve) =

100

425600)18.1(36.2:

weightsampletotal

micronsmicronsmmmmweighteachweightsampletotal

And so on to the bottom. Don't forget what is retained in the pan; it has to be plotted too!!!

3. Report if there is a predominant fraction in one size range, over 20% of the total samplesay,

i.e. if 35g of 115g sample is retained by the 600 micron sieve, the sample is predominantlysandy

% (600 micron sieve) = 35/115 x 100 = 30.43%

Sand ranges from 0.06mm to 2mm.

4. Plot the cumulative percentage passing versus sieve size on the Grading Curve graphprovided.


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Part A: Results.

Page 4 and 5 are to be handed in as part of your lab assignment.

Table 1 Calculation of Percentages Passing.

Sieve Size(microns)

Weight of Sieveand Sample (g)

Weight of Sieve(g)

Weight of Sample(g)

% Passing

2.36 mm

1.18 mm

600 microns

425 microns

300 microns

150 microns

75 microns

Passing

TOTAL

Predominant Particle Size =


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Figure 2 Grading Curve.


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Part B Atterbergs Limits.

Fine-grained soils are found in four moisture states:

Liquid - a Slurry which will flow like water

Plastic - a Sticky mass which flows under pressure

Semi Solid - a Workable material which has almost brittle behaviour

Solid - a Stiff structured mass

The strength of a soil tends to decrease as its moisture content is increased. In other words,foundations, which are inundated with water, lose their bearing capacity and can fail.

Conversely, the volume of a soil mass tends to expand as its moisture content is increased.

Foundations heave after wet weather and subside during a drought.

Figure 3 Volume changes in relation to moisture content.

The dividing points between the states, shown in figure 3 above, were defined by Atterberg in thefirst decade of the twentieth century. If a soil in the liquid state is gradually dried out, it will passthrough the Liquid (LL), Plastic (PL), and Shrinkage (SL) Limits before it finally reaches the solidstate.

Atterberg devised standard tests to measure the Liquid, Plastic and Shrinkage Limits in terms ofwater content. The tests are only performed on the fine fraction of the soil; soil particles which are

smaller than 425 microns (0.425 millimetres) in diameter. For example, the Liquid Limit is reportedin terms of the water content at which the soil grains resistance to viscous flow; when it changesfrom the liquid to the plastic state.

The difference in the moisture contents between the Liquid and Plastic Limits is particularlyimportant it is called the Plasticity Index (PI). It measures the range of moisture contents overwhich a soil can be moulded without cracking. Indirectly, it is an indication of the activity of a soil.Highly reactive soils have a large Plasticity Index (30, say) The Liquid Limit is much higher thanthe Plastic Limit.

Highly reactive soils can cause footing movement. It can translate into the superstructure causingfunctional elements, like doors and windows, to jam and brittle structural elements like unreinforcedconcrete, glass and plasterboard, to crack.


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SECTION 1 LIQUID LIMITS.

Equipment.

400 g electronic balance 1 Off

Mixing bowl 2 Off

Wash bottle 2 Off

Spatula 2 Off

Liquid limit apparatus complete with grooving tool 2 Off

Oven 1 Off

Oven dishes

Marking pens

Methodology.1. Determine the weight of an empty crucible M1. Clearly mark the name of your group and

the type of test on the crucible.

2. Place a sample of 50g of pre-wet soil (passing 425 micron sieve) in a mixing bowl.

3. Add water until the sample has the consistency of whipped butter. Mix the water into thesample for 5 minutes.

4. Place the sample in the apparatus cup and level off. The grooving tool is then drawnthrough the sample on a diameter from the back to the front of the liquid limit device. Thegrooving tool should be held so that it is always at right angles to the surface of the cup.

5. Crank the apparatus and count the number of blows required to close the groove over

10mm. (Refer to figure 4 for clarification).

6. Repeat the test until the number of blows from successive tests varies by a maximum of 2.

Figure 4 Liquid Limit test apparatus.

7. After the test, 20g of sample is taken from the area around the point of closure.

8. Determine wet weight of sample and crucible M2 and dry in the oven after the sample hasbeen clearly marked to identify your group.

9. Data on the dry weight M3 will be provided on vUWS 2 days after the practical againstyour particular group leaders name.


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Calculations.

1. Determine the percentage moisture content of the sample. Use Table 3 for yourcalculations.

10013

32

..

MM

MMW LL

2. The liquid limit test is based on the moisture content required to close the groove in 25blows. If the number of blows was not 25, use Table 2 to adjust the moisture content.

factorcorrectionWW LLLL ..1

..

Table 2 Adjustment factor for number of blows.

Number of blows Factor Number of blows Factor

15 0.95 26 1.00

16 0.96 27 1.01

17 0.96 28 1.01

18 0.97 29 1.02

19 0.97 30 1.02

20 0.98 31 1.02

21 0.98 32 1.03

22 0.99 33 1.03

23 0.99 34 1.03

24 1.00 35 1.03

25 1.00


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SECTION 2 PLASTIC LIMITS.

Equipment.

450 mm square x 10 mm thick frosted glass plate 2 Off

Mixing bowl 2 Off

Wash bottle 2 Off

Spatula 2 Off


Oven 1 Off

Oven dishes

Marking pens

3 mm diameter metal rod 2 Off

Air-tight containers

Methodology.

1. Determine the weight of an empty crucible M4. Clearly mark the name of your group andthe type of test on the crucible.

2. Take a ball of soil of about 8g and mould it between your fingers.

3. Roll the ball between the palms of your hand until it has the elasticity of plasticine.

4. Roll the ball on the glass slab until:

a) The thread disintegrates before it is 4 mm in diameter.

The thread is too dry, discard.

b) The thread rolls down to 2 mm without breaking.

The thread is too wet reconstitute and roll down again.

c) The thread breaks at a diameter of 2-4 mm.

Store thread in air-tight sample jar.

5. Collect enough threads to provide a sample of at least 20 g (generally 4 threads aresufficient).

6. Determine the wet weight of the sample and crucible M5.

7. Place sample in oven after it has been clearly marked to identify your group.


Calculations.

1. Determine the percentage moisture content. Use Table 3 for your calculations.

10046

65

..

MM

MMW LP

2. Calculate the plasticity index.

...... LPLL WWIP

3. Plot the test soil on figure 5 Casagrandes plasticity chart.


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SECTION 3 SHRINKAGE LIMITS.

Equipment.


Mixing bowl 2 Off

Hand spray bottle 2 Off

Spatula 2 Off

250 mm long x 25 mm internal diameter

Brass shrinkage troughs 6 Off

Drying Oven 1 Off

Petroleum Jelly

Methodology.

You are required to make up at least three samples of increasing moisture content.1. Place 500 g of soil in a mixing bowl. Slowly add 25 ml of water from a wash bottle and mix

for at least 5 minutes. (Repeat the test 2 more times adding an extra 25 ml more watereach time). Sieve the soil through a 2.36 mm sieve and if the soil starts to form nodules,break them up.

2. Measure the empty weight of the troughs M7 and the length of the mould in millimetres.

3. Grease the inside of a clean shrinkage mould with petroleum jelly and place the wet soil init. Slightly overfill the mould and then compact the soil into the trough with your finger.Remove all the soil adhering to the rim of the mould.

4. Measure the wet weight of the sample and weigh the trough, M8.

5. Place the specimen with the other shrinkage samples after it has been clearly marked toidentify your group. The specimen will be air-dried for 24 hours before it is transferred tothe oven. Than sample is dried at 105C.


7. The longitudinal shrinkage LS will be measured by the laboratory staff to the nearest1mm and the results will be posted on vUWS 2 days after the practical against yourparticular group leaders name.

If the specimen cracks into pieces, the separate parts are held together to measure theshrinkage LS.

If the specimen curls, the sample is carefully removed and the lengths of the top andbottom surfaces are measured. The mean of the two measurements is subtracted from theinternal length of the mould to obtain the shrinkage LS.

8. Repeat the steps above for three (3) sample; adding 25 ml of water each time.


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Calculations.

1. Determine the percentage of moisture content. Use Table 4 for your calculations.

10079

98

..

MM

MMW LP

2. Calculate the percentage linear shrinkage SLof the specimen from the following formula:

L

LS SL

100.

Where: L is the length of the mould in millimetres

LS is the mean longitudinal shrinkage in millimetres

3. Plot the data of percentage linear shrinkage versus moisture content on Figure 6.Determine the approximate moisture content at which shrinkage does not occur theShrinkage Limit.


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Part B: Results.

Page 12 and 13 are to be handed in as part of your lab assignment.

Table 3 Plasticity Calculations.

Test Crucible Weight(g)

Wet Weightincluding

crucible (g)

Dry weightincluding

crucible (g)

MoistureContent %

Liquid Limit

Plastic Limit

Plasticity Index =

Figure 5 Casagrandes plasticity chart.

Soil type =


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Table 4 Moisture calculations for Shrinkage Limit.

Test Trough Weight

(g)

Wet Weightincluding trough

(g)

Dry weightincluding trough

(g)

Moisture Content%

Sample 1

Sample 2

Sample 3

Table 5 Shrinkage calculations for Shrinkage Limit.

Test Trough length (mm) Sample Shrinkage (mm) % Shrinkage

Sample 1

Sample 2

Sample 3

Figure 6 Graph of soil shrinkage.

Shrinkage

10.0%

8.0%

6.0%

4.0%

2.0%

0.0%

0.0% 5.0% 10.0% 15.0% 20.0%

Moisture Content

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