Plasticity Index Test ASTM D4318

Explanation
The scale used for the plasticity index test should be readable to 0.01g. This means that the scale should be sensitive enough to measure weight differences as small as 0.01 grams. This level of precision is necessary in order to accurately determine the plasticity index of a soil sample, which is a measure of its ability to undergo deformation without cracking or breaking. A more coarse scale, such as 1g, would not provide the necessary level of accuracy for this test.

Explanation
The correct answer is 60°C. When using the dry preparation method, the sample is dried back at a maximum temperature of 60°C. This temperature is chosen to ensure that the sample is dried thoroughly without causing any damage or degradation to the sample. Drying at higher temperatures could potentially alter the composition or properties of the sample, which could affect the accuracy of the analysis. Therefore, it is important to follow the specified temperature guidelines for the dry preparation method.

Explanation
After drying the sample, it is ground up with a rubber pestle to break it down into smaller particles. The sample is then separated over a #40 sieve. The sieve size refers to the number of openings per linear inch in the sieve screen. In this case, a #40 sieve means that there are 40 openings per linear inch. This sieve size is commonly used in various industries to determine the particle size distribution of materials.

Explanation
After the soil has been pulverized and separated over the appropriate sieve, it needs to reach a moisture condition that can withstand 25 blows from the liquid limit device. Once it reaches this moisture condition, it should be further tested to see if it can withstand 35 blows from the liquid limit device.

Explanation
After the sample is moisture conditioned, it is covered and allowed to sit for a minimum of 16 hours. This suggests that the moisture conditioning process requires a specific duration of time for the sample to properly condition. This duration is crucial in order to achieve accurate and reliable results in whatever testing or analysis is being conducted on the sample.

Explanation
In the liquid limit test, the soil is spread in a cup to determine its liquid limit. The maximum depth of the soil in the cup should not exceed 10 mm. This is because exceeding this depth could lead to inaccurate results or difficulty in determining the liquid limit accurately. By keeping the maximum depth at 10 mm, it ensures that the soil is evenly spread and allows for easier measurement and analysis.

Explanation
The liquid limit cup drop rate refers to the number of drops that fall from the cup per second. In this case, the correct answer is 2 drops/sec, indicating that two drops fall from the cup every second.

Explanation
When spreading the soil in the cup, it is important to avoid air bubbles because they can affect the accuracy of measurements or the growth of plants. Air bubbles can create pockets of air in the soil, which can hinder the flow of water and nutrients to the roots. This can lead to uneven distribution of resources and potentially affect the health and growth of the plants. Therefore, it is important to ensure that the soil is spread evenly and without any air bubbles to promote optimal plant growth.

Explanation
During the liquid limit test, it is important to cover the unused portion of the soil with a wet towel. This is done to prevent the soil from drying out, as the test requires the soil to be at a specific moisture content. By covering it with a wet towel, the soil remains moist and the test results are more accurate.

Explanation
The correct answer is 25 to 35, 20 to 30, 15 to 25. The moisture content needs to be adjusted so that the groove closes earlier (at a lower number of blows) for the first point compared to the second point. This indicates that the soil is becoming more compact and cohesive with increasing moisture content. The given range of moisture content values (25 to 35, 20 to 30, 15 to 25) suggests that the soil should have a slightly higher moisture content for the second point compared to the first point, and an even higher moisture content for the third point.

Explanation
The given statement is true. After adjusting the moisture content to close at the approximate number of blows, a sample semi-logarithmic graph is taken from the cup. The water content is then performed on this graph in accordance with ASTM D2216.

Explanation
The moisture content and number of blows for each of the 3 points are plotted on a graph. The line on the graph crosses at a point where the number of blows is 25. This represents the moisture content that is the liquid limit.

Explanation
The liquid limit is reported to the nearest whole number because it is a measure of the moisture content at which a soil changes from a liquid to a plastic state. The liquid limit is determined through a standardized test called the Casagrande method, which involves repeatedly dropping a cup of soil from a certain height and measuring the number of blows required for the soil to close a groove of a specific length. Since the test involves counting the number of blows, the result is reported as a whole number.

Explanation
The plastic limit thread must be rolled out on a ground plate that is at least 12 inches square and 3/8 inches thick. This requirement ensures that the thread is rolled out on a stable and consistent surface, allowing for accurate measurements and reliable results. Using a smaller or thinner ground plate may lead to variations in the measurements and compromise the accuracy of the plastic limit determination. Therefore, the statement is true.

Explanation
In order to run the plastic limits test, a sample of 20 grams or more needs to be removed from the liquid limit material. This is because a sufficient amount of material is required to accurately determine the plastic limits, which include the plastic limit and the shrinkage limit. With a sample size of 20 grams or more, the test can be conducted effectively and provide reliable results.

Explanation
For each plastic limit test, a 1.5 to 2.0 gram ball is removed from the sample and formed into an ellipsoidal ball.

Explanation
The correct answer is 1/8. When the elipsoidal ball is rolled between your fingers or palm on the ground glass plate, the thread crumbles at a diameter of 1/8 inch.

Explanation
The given statement is true. The pieces from the thread are molded into a ball and rolled again until they will no longer roll into a thread. This suggests that the thread is being reformed and reshaped repeatedly until it reaches a point where it cannot be rolled into a thread anymore. Therefore, the correct answer is true.

Explanation
The minimum weight of plastic limit test shall be 6 grams. This means that when conducting a plastic limit test, a minimum of 6 grams of the soil sample should be used. This weight is necessary to ensure accurate and reliable results in determining the plastic limit of the soil. Using a lower weight may result in errors or inconsistencies in the test.

Explanation
The plastic limit is indeed calculated using the results of 2 test specimens. This is because the plastic limit is the moisture content at which a soil changes from a plastic state to a semi-solid state. To determine this, two test specimens of the soil are used: one specimen is dried and the other is wetted. The moisture content at which the soil can be rolled into a thread of 3mm diameter without breaking is considered the plastic limit. Therefore, the correct answer is true.

Explanation
The plasticity index is calculated by subtracting the plastic limit from the liquid limit. The plastic limit represents the water content at which a soil transitions from a plastic state to a semi-solid state, while the liquid limit represents the water content at which the soil transitions from a liquid state to a plastic state. By subtracting the plastic limit from the liquid limit, we can determine the range of water content within which the soil exhibits plastic behavior.