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Geomorphology and Soils (GG282)
Part One of GG282 Laboratory Exercise Two
Soil and Surficial Material Physical Properties
Organic Carbon Content, Moisture Content, and Atterberg Limits (Consistency)
Before your next lab, complete and submit this lab’s exercise (GG282 Lab 2 Part 1 Data.xlsx).
Submit your.xlsx file to the DropBox account for YOUR lab area!
Students reviewed the process for determining moisture content in a sediment (soil) sample during the lab time and completed tests to determine the plastic and liquid limits (Atterberg Limits). Students will also watch a demonstration of how to determine the organic content of a soil sample.
We’ll compute the moisture and organic content of the samples, as well as the liquid and plastic limits, this week in the lab. We’ll also begin the process of pooling our experiment’s data. This project will be continued at the start of next week’s lab.
Atterberg Limits Moisture Contents
In the room, there were three samples labeled Sample 1, Sample 2, and Sample 3. Three trials for the liquid limit determination and three trials for the plastic limit determination were conducted for each sample in each lab section.
Moisture Content (Task 1)
Each student would have access to a data table with sample weights. Normally, we would combine the data from your lab part. Sample ID, dry tin weights, and wet sample and tin weights would have all been weighed on your table. You would take the samples from your lab section’s drying oven and weigh the dry samples and tins on the balance. Following that, you would have inserted the data into the data table. Calculate the dry sample weight and moisture weight for each sample. For each sample, you will determine the moisture content in percentages. To complete the table, enter all of these values. On the data sheets, show one complete set of calculations.
Task 2: Calculating the Liquid Limit
The moisture content of the sample (soil) at which 25 blows (drops) on the Casagrande apparatus close a grove over a distance of 13 mm is known as the liquid limit (one-half inch). In actuality, preparing a sample with just the right moisture level such that the groove closes in exactly 25 blows is extremely tough.
The liquid limit can be determined using one of two methods based on the type of data collected with the Casagrande apparatus:
An empirically generated equation is used to find the liquid limit (see below). This equation is based on data from hundreds of fine-textured samples (L.E.J Norman (1959), The One-Point Method of Determining the Value of the Liquid Limit of a Soil, Geotechnique, Volume 9, Issue 1, pp. 18).
The moisture content at n blows is used to compute the liquid limit (LL) (wn). The moisture content of the soil is measured as a percentage of the weight of the oven-dried soil. When you calculate the liquid limit, you’ll get a value that’s also a moisture content in percent.
We(N/25)0.121 = LL
LL stands for Liquid Limit in Percentage.
We = Percentage of the sample’s water content at n blows
N is the total number of blows required to shut the grove in the test.
To utilize this expression, use the number of blows (N) to close the groove in the test and the moisture content of the sample from the liquid limit test (Wn).
In one experiment, the grove closed over the time interval and a sample was taken. The sample had a moisture level of 35% and a total of 21 blows to seal the grove. The sample’s liquid limit is 34.3 percent, according to the expression above.
Determine the liquid limit for each of the three trials using the one-point technique for the three samples used in your lab section. Fill in the blanks in the attached table. One set of calculations is displayed.
Task 3: Establishing a Plastic Limit
The moisture content at which a soil or silt begins to behave like a plastic material is known as the plastic limit. In response to an applied stress, a material that exhibits plastic behavior undergoes a non-reversible change in shape (strain). Fine-grained soils and sediments are semi-solid at moisture levels just below the plastic limit. The plastic limit is expressed as a percentage of moisture content. We used the method provided in the last handout to determine the plastic limit.
When a soil sample is weighed, dried, then re-weighed at its plastic limit, the weight loss of the soil sample equals the moisture lost during drying. By dividing the weight of the moisture loss proportionally to the mass of the oven-dried soil, the moisture content at the plastic limit can be estimated as a percentage.
Task 4: Calculating the Plasticity Index
The Plasticity Index (PI) or Plasticity Number is the numerical difference between the liquid and plastic moisture content:
PI = Moisture Content at Liquid Limit – Moisture Content at Plastic Limit
Organic Content (Task 5)
The organic content was determined using five soil samples. In each lab segment, one or two trials were done for each sample; each sample received eight trials over the course of the week. The information has been recorded into a spreadsheet that may be found on XDrive.
Open the spreadsheet with the loss on ignition data that you downloaded from MLS.
(GG282 Lab 2 LOI Data 2020.xlsx). Examine how the data in the spreadsheet is organized. The following calculation is used to compute the proportion of organic matter in each sample:
Organic Substances ( percent )
= (pre-combustion soil weight) – (post-combustion soil weight) / 100
(pre-combustion soil weight)
Examine the data in the existing columns in the spreadsheet, and then:
1) Calculate the soil pre-combustion weight for each trial.
2) Calculate the weight of organic matter lost during burning for each trial.
3) Calculate the soil post-combustion weight for each trial.
4) Calculate the organic matter percentage for each trial.
5) For each sample, calculate the average organic matter percentage.
Examine the outcomes. There are five samples in all, each with eight or nine trials. Is there anything that stands out as an outlier among the trials? To find these trials, search for values that are significantly different from the rest of the sample.
Determine the mean organic matter content as a percentage for each sample, then repeat the computations after eliminating any abnormal values. Demonstrate a single example of your work.