Constant Head Permeability, Sieve Analysis and Liquid Limit Practicals ENB272 – Geotechnical Engineering

Tim Starkey n8588163

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Table of Contents

Practical 1 – Sieve Analysis Test .................................................................................... 3 Equipment ...................................................................................................................................... 3 Materials ......................................................................................................................................... 3 Procedure ....................................................................................................................................... 3 Calculations and Discussions .................................................................................................. 3

Practical 2 – Constant Head Permeability Test ........................................................ 5 Equipment ...................................................................................................................................... 5 Materials ......................................................................................................................................... 5 Procedure ....................................................................................................................................... 5 Calculations and Discussions .................................................................................................. 5

Practical 3 – Liquid Limit Test........................................................................................ 7 Equipment ...................................................................................................................................... 7 Materials ......................................................................................................................................... 7 Procedure ....................................................................................................................................... 7 Calculations and Discussions .................................................................................................. 8

Appendices ......................................................................................................................... 10

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Practical 1 – Sieve Analysis Test This test is carried out to determine the percentages present of various sizes (governed by sieves used) of particles in soil (generally on soil particles coarser than 75μm)

Equipment The equipment required to undertake this test were:

Set of sieves with different mesh opening sizes Brush to clean sieves Electronic balance Shaker to shake that stack of sieves Oven to dry soil Watch (or Stopwatch)

Materials This practical required the following materials:

Dry Sand

Procedure

To perform this test, the following procedure was followed: a. Select a set of sieves and clean them b. Measure the weight of each sieve and record c. Stack the sieves in the shaking apparatus d. Obtain about 700 ~ 1000g of dry sand and pour it into the top sieve in the

stack (Note: measure and note exact mass of sand before putting it into the top sieve)

e. Close the top sieve by using a lid and shake the stack of sieves for 3 ~ 5 min f. Measure the mass of each sieve with retained sand and record the values g. Remove the retained sand in each sieve and clean sieves Note: You are provided oven-dried sand for this test and can assume zero water content

Calculations and Discussions (1) Data Sheet Dry Mass of Test Sample = 999g Sieve Size (mm)

Mass of Sieve (g)

Mass of sieve + retained soil (g)

Mass of retained soil (g)

Cumulative retained mass

Cumulative % retained

% passing

4.75 1004 1025 21 21 2.1 97.9 2.36 1060 1156 96 117 11.7 88.3 1.18 961 1204 243 360 36.1 63.9 0.6 921 1158 237 597 59.8 40.2

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0.425 835 992 157 754 75.5 24.5 0.3 790 897 107 861 86.2 13.8 0.212 774 868 94 955 95.7 4.3 0.15 765 801 36 991 99.3 0.7 0.075 773 779 6 997 99.8 0.2 Pan 791 792 1 998 100 0 (2) See Appendix 1 for ‘Percentage Finer vs Particle Size’ (3) Using the ‘Percentage Finer vs Particle Size’ graph, the values for D10, D30, D50 and D60 can be obtained. See Appendix 1 for how these values were obtained. D10= 0.28mm D30= 0.49mm D50= 0.79mm D60= 1.05mm (4) The permeability of this test soil can be calculated using Henzan’s equation:

Therefore:

(5) Using the different values of ‘D’, the Coefficient of Uniformity (CU) and the Coefficient of Curvature (CZ) can be calculated for this sample using:

And

Therefore, CU is calculated as:

And CZ is calculated as:

(6) Using the Unified Soil Classification System (USCS), this soil sample can be given a classification according to its grain size. This sample is classified as Poorly Graded Sand because more than 50% of its coarse fraction is smaller than 2.36mm and its percentage of Fines is smaller than 5%. This classified it as Clean Sand but it couldn’t be graded as Well Graded Sand as its CU and CZ were too small (see Appendix 2).

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(7) Due to the grading of the soil sample, there are limited applications for this material. As it couldn’t be graded particularly well, the sample would not be appropriate for aggregate as there is a limited range of particle size. However, a more appropriate use for this graded soil is Sand Fill, the use of sand to fill in large spaces. Because of the small yet uniformed grain sizes, the soil could be easily compacted down to levelled ground, ideal for laying a slab for construction. Another use for Poorly Graded Sand is a natural sand filter. These filters are used in a large variety of water filtration situations on and off construction sites. Placed in water run offs, sand filters remove a large majority of the potential biohazard waste out of water flowing of a construction site. Stopping hazards such as litter, chemicals and oils from running into water streams and preventing contamination.

Practical 2 – Constant Head Permeability Test

Equipment The equipment required to undertake this test were:

Permeameter Watch (or Stopwatch) Electronic Balance Graduated Cylinder Thermometer

Materials This practical required the following materials:

Sand (obtained from the same batch used for sieve analysis)

Procedure a. Adjust the height between the constant head water tank and the permeameter

cell

b. The cell is then subjected to water flow under a constant head

c. The test should commence with a small flow by opening the inlet and then the

outlet taps a little; adjust these to get a constant and steady head difference on

the manometers

d. Using the graduated cylinder, measure the volume of water collected in about

10 sec and then measure the temperature of collected water

e. Repeat step d for about 20 sec and 30 sec

Calculations and Discussions (1) Data Table Internal diameter of Permeameter cell (D)

7.35 cm

Height of Soil Specimen 19 cm Dry mass of Soil 1340g Reading of manometer 1 (H1) 16.5cm

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Reading of manometer 2 (H2) 35.5 cm Distance between two manometers

11 cm

Trial Number

Elapsed time, t (sec)

Volume of discharged, Q (cm3)

Water Temperature, T (°C)

1 15 85 23 2 20 115 23 3 25 135 23 (2) Permeability, k, can be calculated using the equation:

Where: kT = coefficient of permeability at the average temperature,

T (cm/sec) L = Length between two manometers (cm) t = the average time for discharge (sec) Q = the average volume of discharge (cm3) A = cross-sectional area of permeameter (cm2) ΔH = the total head different across length L (cm)

By using this calculation, the permeability of the specimen can be analysed.

(3) The viscosity of water changes with temperature. As temperature increase, viscosity and permeability increases. The coefficient of permeability is standardised at 20°C and the permeability at any temperature T is related to k20 by following the ratio:

Where: ηT and η20 = The viscosities of water at the temperature, T,

of the test and at 20°C, respectively. These values can are looked up in a table (see Appendix BLAH)

Using this calculation, we can calculate k20:

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(6) When looking at permeability, there are a few real-world engineering situations which the information recorded and calculated can be used in. Some situations that require known permeability of soil include:

Foundations during Construction Dams and Reservoirs Man-made Islands

Without knowing the permeability of soil in these situations, construction of any infrastructure would be impossible. When constructing a large building, foundations are usually built deep into the ground to account for any forces on the structure. These foundations can be dug tens of metres into the ground depending on the height of the building. During this stage of construction, if the foundations are built so deep that they are under the water table, water will begin to seep up into the site through the soil. Without knowing the permeability of the soil underneath a construction, engineers would not be able to design the foundations strong enough to hold back the force of the water through the soil. If the soils permeability is too strong or the surface area of the foundation is too large in relation to its mass, the structure will essentially float on the water permeating through the soil. Similar to building foundations, the permeability of the soil at a site for a dam needs to be known so that the right height to depth is used. If too much water is being stored behind a dam that is too “skinny”, the amount of water permeating through the soil will cause the dam to float, leading to a catastrophe. The permeability of the soil used to build a man-made island is crucial to the construction. If soil that is too permeable is used, more of it would be required to build enough of a foundation up to produce an island. The higher the permeability of the soil, the larger the effect of erosion will be on the structure.

Practical 3 – Liquid Limit Test

Equipment The equipment required to undertake this test were:

Cone Penetrometer Watch (or Stopwatch) Electronic Balance Small Container for soil drying Oven Vernier Calliper

Materials This practical required the following materials:

Pottery Clay

Procedure a. Fill the cup with clay and struck off level

b. Measure the mass of the cup with soil (M1) and record it

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c. Place the cup under the cone and lower the cone point to the surface, then

lower the dial gauge stem to bring in contact with the penetrometer; take the

initial dial gauge reading and record it.

d. Release the cone for 5 sec and record the dial gauge reading (take the

difference of the initial and final dial gauge readings to get the penetration of

the cone into the soil)

e. Measure the mass of empty container (m1) and record it, take some soil from

the cup and put into the container and measure the mass of container with wet

clay (m2). Oven dry this soil for about 24 h and measure the mass of the

container with dry soil (m3).

f. Clean the cup for next group

Calculations and Discussions (1) Data Sheet Mass of the empty cup (g) 251.09 Mass of the cup with clay (g) 417.66 Diameter of the cup (mm) 53.80 Height of the cup (mm) 40 Date: 10 April 2013 Time of prac 6 - 8 Sub-group No.

Cone Penetration (mm) 5 sec

Container Number

Mass of the container (g)

Mass of container + wet soil (g)

Mass of container + dry soil (g)

1 22.91 44 23.02 30.47 28.2 2 17.7 210 23.35 34.02 31.05 3 11.23 47 22.43 30.96 28.66 (2) Water Content in Specimens Sub group No. Cone Penetration (mm) Water Content (%) A 22.91 30.0 B 17.7 27.9 C 11.23 27.0

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(3) ‘Water Content vs Penetration’ Graph

(4) To calculate the dry density of the soil used in the test, the total density must first be calculated. For the total density to be calculated, the volume and mass of the sample has to be analysed. Therefore:

Now that the mass and volume of the sample has been calculated, the total density of the clay can be analysed. Therefore:

⁄

From the total density, the dry density of the sample can be calculated using the following formula:

7.45 8.74

7.43

1

10

1 10 100

Wa

ter

Co

nte

nt

(%)

- L

og

Sca

le

Penetration (mm) - Log Scale

Water Content (%)

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Where: w = Water Content The water content of the sample is calculated by:

Using the water content calculated for the clay sample, the dry density of the sample can be calculated. Therefore:

⁄

(5) When performing this test, there are a few factors that could cause error in the data collected. These errors consist of:

Human Error Cone Positioning Voids

Human error in this test would include errors in measurements such as weight and dimensions, along with anything else in the test that required human set up and placement. When positioning the cone to just touch the sample there is no way to determine whether or not it is just touching. This leads to a slight error in the measurement of penetration. Because this is not consistent over the three groups, the overall results will be slightly out from each other. When filling the cup up with the clay, small voids could have been formed. These small voids would affect the amount of penetration in the sample. Along with filling the cups up, these voids could also be a natural occurrence in the clay itself.

Appendices