Tests to Analyse and Classify the Plasticity, Particle Size and Engineering Properties of Soils

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The University of Sydney *

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2410

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Chemistry

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Jan 9, 2024

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Tests to Analyse and Classify the Plasticity, Particle Size and Engineering Properties of Soils CIVL2410 Soil Mechanics: Classification Lab Report SID: 510460929 1.1 Abstract This report describes the experiments regarding plasticity and particle size analysis, specifically through the experiments of Cone Penetrometer, Atterberg Tests, and Sieving and Hydrometer Tests. The aim of these experiments was to use experimental methods to classify and identify the engineering properties of given soils. Through the examination of the moisture contents present within the soil, and the examination of the particle sizes for another sample, the soils were classified through the Unified Soils Classification Systems (USCS). The liquid limit, plastic limit and plasticity index were identified for a set of sample soils, whereas the grading curve was determined for another sample of soil. By examining the grading curve, the soil sample which exhibited behaviours of sand, displayed the composition of the typical grading curve of C: Well graded with some clay. Examining the plasticity of another soil sample, which exhibited behaviour of clay, found that through the discovery of its plastic and liquid limits, it was determined that the soil was an inorganic clay with high plasticity. The liquid limit was on average 56.9 with an accompanying plastic limit of 19.8 with an average plasticity index of 37.1. This was used within the USCS to classify that the soil was an inorganic clay (CH).
2.1 Introduction Soil is a particulate material with engineering properties that are difficult to control. Classification is undertaken to understand the likely behaviours of specific soils. It is important that engineers understand these behaviours to determine the limitations of the soil which they must work with. Fine and coarse grained soils observe differences in the ability to resist plastic deformation, as well as differing in strength and stiffness. These differences in properties lead to different usability depending on a soils classification. By undertaking experiments following the Australian Standard AS1289 Section 3, in conjunction with Unified Soil Classification System (USCS), the plasticity and particle size of a given soil core sample can be determined. A sieve and hydrometer experiments were undertaken to determine the grading curve of the provided cohesionless soil. Atterberg tests alongside a cone penetrometer test were performed on cohesive soils to determine the plastic and liquid limits of the given soil. The aim of these experiments was to classify the provided soil to gain an understanding of the engineering properties and the practical usability of the soil.
3.1 Methodology 3.1.1 Plasticity: Liquid Limit - The “25 Blows” Method To begin the experiment, measure eight little trays which will hold the soil samples. These trays should be labelled and their weights should be recorded. For the plasticity experiment, use three samples of soils which have been premixed with nominal water which are close to the liquid limit. Choose one of the soil samples and place a little sample inside of the liquid limit apparatus and level it out so that the height of soil is level with the apparatus base. Using a standard grooving tool, create a groove within the soil by scraping to the bottom of the bowl. Once the groove has been created within the soil, rotate the handle of the apparatus twice per second, until the groove has closed up. During this process, count the blows of the apparatus until the groove has closed. Record the amount of blows and clean out the bowl. Repeat the same experiment with the same sample until the amount of blows between two consecutive tests is not greater than one. Use a small sample from the bowl and place it into a tray and weigh the tray with the soil. Repeat this for each different soil sample and record the amount of blows (Appendix 1.1). 3.1.2 Plasticity: Liquid Limit - The Cone Penetrometer Method Choose one of the soil samples and fill up a small container and level the top surface of the soil. Place the container within the penetrometer and lower the cone so that it just touches the surface of the soil. Set the dial gauge to zero, and release the cone for five seconds, and then lock it. Record the final penetration value (Appendix 1.2) and use one of the eight little trays and put in a small sample from the container. Reset the cone, and repeat the experiment with the different soil samples. 3.1.3 Plasticity: Plastic Limit - The “Make-a-Snake” Method Weigh a saucer which will be used for later calculations. Using a soil sample which has been dried to near the plastic limit, roll 10 of the soil into a “slug” with a diameter ?? 3 of approximately 5 mm. Continue rolling the “slug” until the diameter is 3 mm. If the soil doesn’t crumble, create a ball with the rolled “slug” and repeat the process again. Once the “slug” crumbles at 3 mm in diameter, flatten 1 of the soil and place it in the ?? 3 saucer and weigh the soil and saucer. Place the saucer inside an oven which has been set on medium heat and leave it in for thirty seconds and weigh the soil again. Change the temperature to medium-low and place the saucer in the oven for twenty seconds and weigh it and repeat the experiments until the weights on successive are at least (<1% difference). Record the values (Appendix 1.3).
3.2.1 Particle Size Analysis: Sieving Using a tub of sandy soil, weigh the soil within the tub and record the mass. Using a set of clean sieves, measure the mass of each individual sieve within the set and record the values. (Sieve sizing in Appendix 1.5). Assemble the sieves in order, and pour the soil into the sieves and place the sieves into a shaking machine for three to four minutes. Disassemble the sieves and weigh each tray with its captured soil. Set aside the bottom sieve for the hydrometer test. 3.2.2 Particle Size Analysis: Hydrometer Before the experiment, measure the mass of a hydrometer. Pour the soil from the bottom of the sieve into a shaker and add approximately 150 ml of distilled water into the shaker. Turn on the shaker for 5 minutes, and after it is finished, place soil into a graduated cylinder. Make sure to clean out the shaker completely and pour as much of the soil into the cylinder. Add water into the cylinder until it is filled to the 1000 ml mark. Cover the top of the graduated cylinder and rotate it vertically to properly mix the soil with the water. As the cylinder is undergoing the mixing, get ready to use the timer. Place the cylinder down and immediately place the hydrometer and thermometer inside and start the timer. At time intervals of 15 seconds, 30 seconds, 1 minute, 2 minutes, 4 minutes and 8 minutes, observer and record the values (Appendix 1.6) for temperature and hydrometer readings on the meniscus. 𝑅'
4.1 Results The following results from the experiments are shown below. Number of Blows Moisture Content (%) Sample Preliminary Final 1 21 22 54.5 2 40 41 53.6 3 41 42 62 Fig. 1: “25 Blows” Experiment Results and Calculated Moisture Content Fig 1 demonstrates the results from the 25 blows experiment in which the highest moisture content came from sample 3, which saw a significantly higher moisture content as compared to sample 2 which had a similar number of blows. Cone Penetration (mm) Moisture Content (%) Sample Test 1 Test 2 Test 3 Average 1 24 23.3 22 23.1 64.4 2 18.6 17.5 18.7 18.3 56.3 3 17.5 16.6 17.4 17.2 53.7 Fig. 2: Cone Penetration Experiment Results and Calculated Moisture Content Fig 2 shows that the cone was able to penetrate deeper with samples with a higher moisture content, demonstrating the plasticity of the soil. Moisture Content (%) Test Microwave Method Standard Method 1 21.5 27.5
2 18.1 17.3 Average: 22.4 Fig. 3: Moisture Content of PL Snake Method Fig 3 shows the results obtained to find moisture content using the “Snake Method”. This would then be used to determine the Plastic Limit of the soil. In comparison to the other testing method, the moisture content is significantly lower. The average of the microwave method values would be taken as the plastic limit ( AS 1289.3.2.1) Sample Water (g) Dry Soil (g) Moisture Content (%) LL 25 Blows 1 3.78 6.93 54.5 LL 25 Blows 2 2.74 5.11 53.6 LL 25 Blows 3 4.65 7.5 62 LL Cone 1 4.98 7.73 64.4 LL Cone 2 5.11 9.08 56.3 LL Cone 3 5.89 10.96 53.7 PL Snake 1 0.11 0.4 27.5 PL Snake 2 0.13 0.75 17.3 Fig 4: Calculated Moisture Content of all Experiments Fig 4 highlights the moisture contents calculated for each experimental method. Cone Penetration test 1 exhibited the largest moisture content, whereas the “Snake” sample 2 exhibited the lowest, displaying the significance of the reduction in moisture content through friction. The moisture content of each experiment were calculated as shown in Appendix 1.4
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