geotech lab report
TRANSCRIPT
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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