geotech lab report

Upload: stephen-abbott

Post on 05-Apr-2018

217 views

Category:

Documents


0 download

TRANSCRIPT

  • 8/2/2019 Geotech Lab Report

    1/5

    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

  • 8/2/2019 Geotech Lab Report

    2/5

    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)

  • 8/2/2019 Geotech Lab Report

    3/5

    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.

  • 8/2/2019 Geotech Lab Report

    4/5

    ()

    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.

  • 8/2/2019 Geotech Lab Report

    5/5

    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