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Experimental design: Record all details related to your experimental design. For each research question, there should be 1 hypothesis. For each hypothesis, there should be 1 experiment. How many levels are there for the independent variable (usually 6 for a significant evaluation of hypothesis)? How do you change the independent variable? How do you measure the dependent variable? Did you carry out a trial experiment? Did you repeat your experiment and take the average to improve accuracy? There are some designs that are unique to your experiment.
Experimental setup: Record all details related to your setup. Include a diagram and any changes to diagram subsequently if your setup should change during the course of the experiment.
Experimental procedure: Record all details related to your procedure. Document your steps, trials, and observations to be made. Make sure that your experimental design steps (e.g. levels of independent variable, repeat experiment) are incorporated to the procedure section. You must also list the procedures on how would you analyse the data, including a table that you will use to tabulate your data, a graph if your hypothesis is correct, and how you will arrive at a statement of how your hypothesis is verified or not.
Be sure and clearly note any modifications you make and any problems you encounter, including any mistakes. Even if it seems trivial or inconsequential, you should write it down in this paragraph.
Experimental design:
There are 6 levels for the independent variable.
We change the independent variable by using acids and alkalis to change the pH levels of the soil samples. However, the pH did not change and so we changed our independent variable to moisture. The moisture still changes because of the acids and alkalis.
We measure the moisture levels of the soil samples using a rapitest 4-in-1 tester.
We do each experiment for each level of independent variable twice. We also repeated our experiment for one moisture level of soil for shear strength as the results were an anomaly.
Experimental setup:
Experimental procedure:
Place newspapers on the worktable to avoid spillage onto the table itself
Measure 1.5 g of sodium bicarbonate using an electronic balance
Pour 1.5 g of sodium bicarbonate into the beaker
Fill the beaker with water until it reaches the 400 ml mark
Mix the two components thoroughly
Put different drops of sodium bicarbonate into each part of the soil
Pour different numbers of tablespoons of vinegar into each part of soil
Cut the soil into twelve equal parts using the wire saw (For shear)
Cut the soil into twelve equal parts using the wire saw (For tensile)
(Shear)
Measure the mass of each part on an electronic balance and note it down in Table 1 and ensure all the masses are equal
Change two parts of soil to a different moisture level with sodium bicarbonate and vinegar
Measure the moisture level of the two parts of soils using the rapidtest 4-in-1 tester and note it down in Table 1
Take one part of the soil as sample A and place it down in container
Ensure that the handheld shear vane’s reading is at 0
Press the spikes of the bottom of the device into the soil surface
Make sure your hand is not placed below knob
Start slowly rotating the device clockwise until the soil matrix fails
Record the value on the scale to the nearest 0.01 kg/cm2
Multiply the reading by the multiplier of the vane size
Record the final value in unit kPa and note it down in Table 1 as Reading 1
Repeat the experiment 1 more time to ensure the reliability of results for the other piece of soil with the same moisture level
Repeat steps 11 to 21 for a total of 6 different moisture levels of soils
(Tensile)
Measure the mass of each part on an electronic balance and note it down in Table 2 and ensure all the masses are equal
Change two parts of soil to a different moisture level with sodium bicarbonate and vinegar
Measure the moisture level of the two parts of soils using the rapitest 4-in-1 tester and note it down in Table 2
Take one part of the soil as sample A and place it between two steel discs, one on the top and one on the bottom
Apply vertical load slowly on the top disc until the soil reaches failure
After that, use this formula to calculate the tensile strength:
where,
sigma t = simple tensile strength
P = applied load
b, H = dimensions found in Fig.2
a = radius of the punch
7.Repeat the experiment 1 more time to ensure the reliability of results for the other piece of soil with the same moisture level
8.Repeat steps 2 to 7 for a total of 6 different moisture levels of soils
Procedure to analyse the data:
On the electronic balance, the mass of soil is recorded in grams. To convert it to kg, which is the required unit for calculation, we divided it by 1000.
For Shear Strength, we had to convert the units from kg/cm² to kPa. To do so, we multiplied the value by 98.066.
Plot the graph for shear strength using the results.
The data points should be the shear strength results
The y-axis should be shear strength results
The x-axis should be the moisture level
For tensile, we measured the distance and time it took for the soil to fail, and we used the values to calculate velocity.
After which, we calculated the acceleration of our hands as we pushed the steel punches in, which was using velocity divided by time.
We also calculated the force exerted by our hands as we pushed the steel punches in by multiplying the mass of the steel punches by the acceleration of our hands, as the formula for force is mass multiplied by acceleration.
We also had to calculate the pressure that the steel punches exerted on the soil. The formula for pressure is the weight of steel punches divided by the surface area of the steel punches. We calculated using the surface area of the steel punches using the surface area of the cone, as the steel punches come in a shape of a cone.
Next, we added the values of the pressure of steel punches with the force value of the force exerted by our hands. This value is called the applied load.
We then used the formula for tensile strength to calculate tensile strength. There was no unit conversion needed.
Plot a graph for tensile strength using the results.
The data points should be the tensile strength results
The y-axis should be shear strength results
The x-axis should be the moisture level
If there is an upward trend for both graphs, then our hypothesis is correct.
To prove whether our hypothesis is correct, we intend to plot graphs for shear and tensile strength using the results that we got and compare them with the graphs above (Graph 1 and Graph 2), which are the results that we intend to get if our hypothesis is correct.
Modifications/Limitations
A problem that we might face during the experiment is the pH not changing, as articles online mention that sometimes it takes months or even years for the pH to change. However, we intend to add more amounts of sodium bicarbonate and vinegar, which are substances that are able to increase and decrease the pH level, in hope that the pH level will change faster.
Unfortunately, the pH level did not change by the fifth day, hence we decided to change our independent variable to moisture. Since we had added different amounts of liquids to the soils, we believed the soils would have 6 different moisture levels. However, some pairs of parts of soils did not have the same moisture levels as they were supposed to because we added the same amount of liquid for them. For the 6 different moisture levels that we were supposed to have, the differences between some levels were not that large.
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