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Assignment 1 with reflections....

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Autumn 2020

48330 Soil Behaviour

Assignment 1 - Phase Relationships and Soil Classification 1. The aim of compacting a fill is to fit as many soil solids into a given volume as possible. Two soils are available as potential fill, one is classified as SW and the other SP. Which would make a better fill? Briefly explain why.

! Drawing 1

! Drawing 2

SW is well graded sand and SP is poorly graded sand. The grade is determined by the fill’s void ratio, where the lower it is, the well graded. Looking at drawing 1, it represents SW fill as it is well graded sand meaning it has more smaller grains to fill the void thus a lower void ratio. Drawing 2 represents SP fill which is poorly graded sand meaning is has less smaller grains. Thus, it has a higher void ratio due to not having as many small grains to fill the voids between the larger grains. As the aim is find the better fill for compacting, we would want the fill with a lower void ratio, as it can be compacted to a higher density. This means it can have a higher load bearing capacity as the fine grains can be vibrated or compacted into the spaces between the larger particles. Thus, SW fill would be a better fill. Reflection: In this question, I have learnt the effects soil grades has on fill compaction. I have also learnt how it is important to determine the void ratio of soils, especially if I were to build a building on top of the soil. This is so I can be aware of how much the soil can compact so I can decide which type of foundation I need to build in order for my building to remain standing. 2. Soil A is classified as GW and soil B as CH. Which soil, A or B, has the highest: ! a) plasticity - Soil B as it is CH, a high plasticity clay. Clay has smaller particle sizes than gravel which has the higher plasticity because it can retain deformation. ! ! b) permeability - Soil A as it is GW, a well graded gravel. Gravel has the higher permeability because it has much larger particle sizes thus, there is more void space within the soil. Reflection: In this question, I have learnt how particle sizes of soils affects soil properties such as plasticity and permeability. As a civil engineer this is essential as I may need to pick a type of soil that has high plasticity for roads because I would not want it to crack under the force of cars. Additionally, I may need to pick a type of soil with high permeability so that water can seep down for better drainage. "

Daisy Tran - 13202282

1 of 10

Autumn 2020

48330 Soil Behaviour

3. A soil sample has a void ratio of 0.6 and a degree of saturation of 75%. Determine: ! a) The total unit weight of the soil sample.! !

Formula for total unit weight of soil sample was obtained from soil mechanics notes. ! !

The void ratio and degree of saturation values were given in the question.! ! Specific gravity of soil is assumed to be 2.65 as it was not provided and unit weight of water on earth is 9.81! ! ! ! ! ! ! ! b) The shrinkage limit of the soil. !

! Formula for void ratio was obtained from soil mechanics notes.

Basic algebra and substitution was done to find volume of solids. As volume of water is assumed equal to volume of voids, volume of water can be obtained by total volume subtracted by volume of solids. Mass of solid formula was obtained from soil mechanic notes where specific gravity of soil is assumed to be 2.65 as it was not provided and density of water is 1.

Formulae obtained from soil mechanics notes and previous values above were substituted in."

Daisy Tran - 13202282

2 of 10

Autumn 2020

48330 Soil Behaviour

Reflection: In this question, I have learnt how to find the total unit of soil sample and the shrinkage limit of the soil by utilising some basic calculations and algebra. It is important for an engineer to be aware of the shrinkage limit of the soil as during rainy weather the soil can shrink or swell up again.

4. A trench 80m long by 0.45m wide by 1m deep is to be excavated in a clay soil at a site. An undisturbed cylindrical sample of the clay, with a diameter of 35 mm and length of 70 mm, is taken prior to digging the trench. The original mass of the sample is 101.5 g where mass of the sample after oven drying is 67.3 g. When the trench is dug the excavated clay will be stockpiles and then used as trench backfill. The clay is to be compacted into the trench in uniform depth layers at a total density of 1.8 t/m3 and a moisture content of 14%. After all the excavated clay is compacted into the trench what depth of the trench will still remain to be filled? ! Volume of the trench is calculated like volume of a prism.

Given dimensions and and values in question.

Formula obtained from soil mechanics notes.

Formula is a volume of a cylinder to calculate cylinder sample.

Density of cylinder sample calculated.

Units converted.

Mass of solids in trench can now be calculated as we have the density and volume of trench"

Daisy Tran - 13202282

3 of 10

Autumn 2020

48330 Soil Behaviour

Given values in question.

Formula obtained from soil mechanics notes.

Mass of water in trench where formula obtained from soil mechanics notes.

Total mass of water and solids inside trench where formula obtained from soil mechanics notes.

Volume of soil in trench that was compacted can now be calculated via given values in question.

Remaining volume can be calculated from original trench volume subtracted by compacted trench volume.

Depth remaining can be calculated via volume of prism formula.

Reflection: In this question, I have learnt how to calculate the remaining depth of the trench that needs to be filled after compaction via a series of basic calculations. It is important for me as an engineer to know how to calculate the remaining depth after compaction as I may need to order more filling so that the trench needs to be filled. If I order too less filling, it would be time consuming to get delivered soil multiple times and if I order too much, I will have excess soil that will go to waste and take up space on construction site. Daisy Tran - 13202282

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Autumn 2020

48330 Soil Behaviour

5. A rectangular excavation measuring 20 m by 40 m in plan is taken down to a depth of 3 m. The sides of the excavation have vertical faces. A cylindrical sample of the soil, with a diameter of 50 mm and height of 100 mm, is taken prior to excavation. The soil sample has an original mass of 363g and mass of sample after oven drying is 310g. ! The excavated soil is to be used to backfill a trench 1 m wide by 2 m deep. The soil is to be compacted into the trench at a moisture content of 24% such that its dry density is 1.6 t/m3. ! a) What would be the shrinkage limit of the soil in the tube sample?! ! ! Volume of trench is calculated like a volume of a prism.

Given values and dimensions in question.

Formula obtained from soil mechanics notes.

Volume of a cylinder is used to calculate cylinder sample.

Formula obtained from soil mechanics notes.

Formula obtained from soil mechanics notes.

Mass of water and volume of water is equal as water is 1g/cm3.

Formula obtained from soil mechanics notes and values obtained above were substituted in. "

Daisy Tran - 13202282

5 of 10

Autumn 2020

48330 Soil Behaviour

b) What length of trench could be backfilled by the excavated soil? ! ! Volume of trench is calculated like a volume of a prism. ! ! ! Density of cylinder sample. ! ! ! ! ! Mass of solids inside whole trench can now be calculated as density and volume is known. ! ! ! ! ! ! ! ! ! Given values in question. ! ! ! ! Formula obtained from soil mechanics notes. ! ! ! ! ! ! ! ! ! ! Total mass is the addition of mass of solids and mass of water. ! ! ! Knowing the density after compaction and mass of solids, total volume can be calculated. ! ! ! ! ! ! !

Length of trench can be calculated via volume of prism formula. "

Daisy Tran - 13202282

6 of 10

Autumn 2020

48330 Soil Behaviour

c) What would be the degree of saturation of the compacted soil in the trench? ! Calculated above in previous question.

Formula obtained from soil mechanics notes.

Formula obtained from soil mechanics notes where calculated values are substituted.

Volume of voids formula obtained from soil mechanics notes.

Formula obtained from soil mechanics notes.

Reflection: In this question, I have learnt how to calculate missing dimensions of a trench I need prepare for the excavated soil to be backfilled and compacted into a trench. As an engineer I always have to plan ahead so that when construction takes place, time is not lost due to disorganisation. Such as when excavating the site, the soil should be backfilled into a trench as soon as possible so that it doesn't take up space on site. Also it is important to save time as a whole day does not need to be dedicated to purely backfilling when I can have someone backfill whilst someone excavates.

Daisy Tran - 13202282

7 of 10

Autumn 2020

48330 Soil Behaviour

6. Classify soils A, B and C according to the USCS. Soil A

Soil B

Soil C

% Finer than 2.36mm sieve

60

80

45

% Finer than 0.075mm sieve

4

60

10

Coefficient of uniformity

5.2

-

4.8

Coefficient of curvature

1.4

-

2.2

Liquid limit

NP

65

40

Plastic limit

NP

45

20

Soil A: - 4% fine grains...