geotech lab report

8/2/2019 Geotech Lab Report

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Stephen Abbott

UB: 10007973

Laboratory Report

Before design can begin on a projects foundation local subsoil samples must be collected and their

properties assessed. By finding out the properties of the local subsoil the engineer can confirm the

suitability of the design. Soil samples can be classified in different ways such as physical properties,

chemical composition and particle size. In this lab tests we focused on the particle size classification,

which can also be referred to as Particle size distribution which breaks the soil samples into 4

different groups depending on their particle size. In the laboratory we tested the particle size of sand

and gravel samples to get their size distribution by using the sieving method, this involved setting up

a series of sieves each with different diameters on the filters (largest being at the top) a sample was

set up at the top layer and then the entire tower was shaken until we were satisfied that the

particles had travelled as far as they could. Taking each sieve in turn we weighed it up and calculatedthe % of the sample that had been retained , this allows us to see how much of the sample would be

classified as gravel or as sand since gravel is classified as having a particle size of greater than 2mm

whereas sand is anything from 2mm to 0.06mm in size. Therefore any particles caught on the 2mm

or less sieves we can assume is gravel unless there is an error with sand particles being loosely

bonded and therefore not passing through the sieves. Tables of the results of the test can be found

below. These show off the amount each sieve size retained both in weight and in percentage of the

final total weight.

gravel

SieveSize(mm) Test 1 Test 2 Average

Avg %retained % Passing

20 0 0 0 0.00 100.00

14 0 0 0 0.00 100.00

10 63.45 57.81 60.63 6.11 93.89

9.5 52.58 44.8 48.69 11.01 88.99

8 280.84 290.04 285.44 39.77 60.23

6.7 326.57 285.06 305.815 70.59 29.41

5 205.9 222.28 214.09 92.16 7.84

3.35 37.25 34.88 36.065 95.79 4.21

2.36 4.16 4.96 4.56 96.25 3.75

Pan 26.02 48.44 37.23 100.00 0.00

total 996.77 988.27 992.52


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Sand

Sieve

Size(mm) Test 1 Test 2 Average

Avg %

retained % passing

2 0 0 0 0.00 100.00

1.18 3.57 2.86 3.215 1.61 98.39

0.6 196.17 196.78 196.475 99.89 0.11

0.425 0.09 0.15 0.12 99.95 0.05

0.3 0.03 0.1 0.065 99.98 0.02

0.212 0.01 0.02 0.015 99.99 0.01

0.15 0 0.02 0.01 99.99 0.01

0.063 0 0.02 0.01 100.00 0.00

pan 0 0 0 100.00 0.00

total 199.87 199.95 199.91

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

0 5 10 15 20 25

% of Gravel Passing

% Passing

Linear (% Passing)

-20.00

0.00

20.00

40.00

60.00

80.00

100.00

120.00

0 0.5 1 1.5 2 2.5

% of Sand Passing

% passing

Linear (% passing)


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Cohesive soils or more commonly known as clay and silt, do not work very well with sieve testing

due to their sticky nature making it very tricky to get particles to fall through the sieves without

sticking to the sieve itself. That and due to the particle size of cohesive soils very fine mesh would be

required for the testing which becomes more expensive and increasingly frail. Particle sizes for

cohesive soils range from 0.06mm to 0.002mm (silt) and less than 0.002mm (clay). Therefore

instead of classicisation via particle size we determine Atterberg limits so we can determine

between clay and slit but this will also result in a plasticity index of the samples. We can find the

liquid limit of a sample by using the falling cone test; this is a more scientific method when

compared to the Casagrande device since it has a reduced change for human error. The falling cone

method finds the liquid limit when the cone can drop to a depth of 20mm through the sample

(British standards). We look for the liquid limit because it gives us the point where the particles start

acting as a liquid rather than a plastic mass, this is due to thin film of water covering the particles,

when enough water has been added (liquid limit) the particles slide past each other with reduced

friction therefore requiring a reduced shear force to deform. From the table of results below we can

see that the initial tests were the closest to the liquid limit, since they were closest in result to apenetration of 20mm

liquid

limit

test

initial dial

reading final dial penetration

mean

penetration

a1 0 20.46 20.46 20.325

a2 0 20.19 20.19

b1 0 22.79 22.79 22.52

b2 0 22.25 22.25c1 0 16.48 16.48 16.62

c2 0 16.76 16.76

d1 0 18.49 18.49 18.24

d2 0 17.99 17.99

Moisture

content

data

test tin nomass oftin

mass oftin+wsoil

mass oftin+dry

mass ofwater soil mass

moisturecontent

meanWc

a1 b48 18.12 26.59 24.32 2.27 6.2 36.6129 36.32713

a2 b68 16.51 25.72 23.28 2.44 6.77 36.04136

b1 b41 18.06 24.31 22.6 1.71 4.54 37.6652 37.26947

b2 b58 17.35 24.18 22.34 1.84 4.99 36.87375

c1 b34 17.57 26.27 23.78 2.49 6.21 40.09662 41.32183

c2 b18 17.88 27.73 24.79 2.94 6.91 42.54703

d1 b8 17.12 24.51 22.28 2.23 5.16 43.21705 43.76539

d2 b59 17.35 24.71 22.45 2.26 5.1 44.31373

By using the same formula for working out moisture content we can figure out the liquid limit.


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()

This gives us a result for the liquid limit as 41.780%.

The other atterberg limit required is the plastic limit; this is the point where the soil sample movesfrom the plastic to semi solid state. This test is done by getting a sample and rolling it out to a

diameter of 3mm, if the sample can be rolled out to less than this then the water content is too high

and the sample needs kneading to reduce the water content. When the samples are ready they are

left in an oven overnight to have their water content removed, this means when we weigh the result

we can calculate what the water content was which will give us the plastic limit, provided all the

water content results are within 0.5% of each other.

Plastic

limit

Test tin nomass oftin

mass oftin+wclay tin+dry

masswater mass soil

moisturecontent mean w

a1 b27 17.87 20.27 19.82 0.45 1.95 23.07692 22.75797

a2 b20 18.24 20.75 20.29 0.46 2.05 22.43902

b1 b95 17.44 19.08 18.76 0.32 1.32 24.24242 24.22167

b2 c40 26.58 29.3 28.77 0.53 2.19 24.20091

c1 b10 17.28 19.3 18.98 0.32 1.7 18.82353 23.01176

c2 b26 17.61 19.2 18.86 0.34 1.25 27.2

d1 b69 17.45 19.99 19.53 0.46 2.08 22.11538 21.94479

d2 c6 15.67 17.18 16.91 0.27 1.24 21.77419

By getting the mean value of the moisture content from all the tests we can get the plastic limit, in

this case the result for the Plastic limit was 22.983%.

With both the liquid limit and plastic limit available to us we can now calculate the plasticity index,

this is a simple formula. Plasticity Index = Liquid limit plastic limit. By using this formula we can get

a result of is 21.797% for the plasticity limit.

Whilst in the laboratory we also performed the Proctor compaction test, this test aims to find the

maximum dry density of the sample and also finds the optimum moisture content for the soil

sample. This test requires we get a dry sample and add a water so it has a small water content

(about 5%) we then fill the container about a 3rd

of the way up before compacting it with 27 blows

from the 2.5kg ram being dropped 300mm each time. We repeat this process of filling the container

up about a 3rd

each time until the sample is fully compacted, this process of filling the container up

in parts allows the entire sample to become fully compacted and free of any trapped air which

would affect the density results. A table for which can be found below.


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Trial 1 Trial 2 Trial 3 Trial 4 Trial 5 Trial 6

Total

Mass of

Soil &

Mould (g)

3923 4051 4220 4220 4179 4096

TotalMass of

Soil in

Mould (g)

1923 2051 2220 2220 2179 2096

Mass of

Container

(g)

10.95 10.51 9.85 11.36 14.51 10.87

Mass of

Container

& Wet

Soil (g)

25.51 30.45 28.45 40.65 45.85 38.65

Mass ofContainer

& Dry Soil

(g)

24.31 28.6 26.38 37.19 41.81 34.82

Soil Mass

(g)13.36 18.09 16.53 25.83 27.3 23.95

Water

Mass (g)1.2 1.85 2.07 3.46 4.04 3.83

References

Liquid limits and fall cones(http://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-104.pdf)

Soil Compaction -http://www.concrete-catalog.com/soil_compaction.html
http://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-104.pdfhttp://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-104.pdfhttp://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-104.pdfhttp://www.concrete-catalog.com/soil_compaction.htmlhttp://www.concrete-catalog.com/soil_compaction.htmlhttp://www.concrete-catalog.com/soil_compaction.htmlhttp://www.concrete-catalog.com/soil_compaction.htmlhttp://pubs.nrc-cnrc.gc.ca/rp/rppdf/t96-104.pdf

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