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Geomorphology and Soils (GG282) is a course about soils and geomorphology.
Part One of the GG282 Laboratory Exercise
Soil and Surficial Material Physical Characteristics
This lab must be finished and turned in before your next lab the following week.
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We’ll look at numerous physical qualities of soil and sediment samples over the course of two weeks in lab exercise two. We’ll do the following things within the first week:
a) show how to test the moisture content of a soil or sediment sample,
b) define consistency and investigate how fine-grained materials alter when exposed to different levels of moisture, and
c) Explain how the organic content of a soil or sediment sample can be determined.
We’ll do the following in the second half of lab exercise 2:
d) sketch out a mechanism for describing soil color
e) show how to determine the pH of a soil
f) show how to determine the proportions of silt and clay in a sample using a method.
The procedures used in the first portion of Lab Exercise Two are described in the following handout.
The Gravimetric Method for Measuring Moisture Content in Soils and Sediments
A ratio of the mass (weight) of water in a particular sample relative to the mass (weight) of the dry soil is most typically used to express the soil moisture content of a soil or sediment sample. Weighing a moist soil sample, drying it to a specified temperature, and then weighing the dry soil’s mass (weight) determines the moisture content. The difference in weight between the wet and dry samples is known as the water mass (or weight). A soil sample is dried in an oven at 105°C for at least 24 hours. The sample will generally evaporate all of the capillary water and most of the structural water at this temperature.
105°C in a drying oven
0.001 g accuracy electronic balance
Weighing tins made of aluminum or a similar container
Field samples of soil or sediment were taken with an auger or similar tools Procedure
Figure 1: In 3C2, Arts Building, a drying oven, and an electronic balance.
1. Write a unique identifier on each aluminum tin, and make sure it’s clean and dry. Prior to use, the tins should have been dried in the oven and stored in a desiccator.
2. Weigh and record the weight of each aluminum tin (the “tin weight”).
3. Fill the tin halfway with a tiny representative sample of the soil or sample, around 5 to 10 g, and note the weight as “wet soil + tin weight.”
4. Dry for 24 hours in a 105°C oven.
5. Cool the sample in a desiccator after removing it from the oven.
6. Once the dried sample has cooled, weigh it and write down the weight as “dry soil + tin weight.”
7. To double-check your procedure, take many samples and repeat the drying and weighing process to guarantee consistent dry weight results.
A “tin weight,” “wet soil + tin weight,” and “dry soil + tin weight” would be assigned to each sample. Data will be provided for you to work with.
We need to know the weight of soil moisture and the weight of dry soil in order to express the moisture content of a soil as a percentage.
Subtract the “tin weight” from the “dry soil + tin weight” to get the weight of the dry soil.
Subtract the “dry soil + tin weight” from the “wet soil + tin weight” to find the moisture content.
The moisture content can then be determined by:
(moisture weight)/(dry soil weight)*100 = Moisture Content ( percent ).
Continuity of Soil
The term consistency refers to how easily a soil can deform when subjected to pressure. https://www.soils.org/publications/soils-glossary/index.html has a glossary of soil terminologies. For uniformity in soil samples, a number of terminologies can be employed (see https://www.soils.org/files/publications/soils-glossary/table-1.pdf, for example). Cohesion and adhesion in a sample are linked to soil consistency (adhesion refers to the attraction of water molecules to the surface of a soil particle, also called adsorption).
We’ll look at one technique to characterize fine-grained soil consistency in this lab (samples). Fine-grained soils have a high consistency when dry (for example, highly hard), but a much lower consistency when wet.
Albert Atterberg, a Swedish soil scientist, studied the physical qualities of fine-grained soils in the early twentieth century, with a focus on consistency. To identify variations that occur when the moisture content of the soil is varied, Atterberg proposed seven “limits of consistency.”
Fine-grained soils can be classified using these parameters (e.g. the Unified Soil Classification System uses Atterberg limits for fine-grained soils). Only the Liquid and Plastic Limits are being measured in practice. The plastic limit in fine-grained soil denotes a transition from a semi-solid to a plastic (flexible) state in soil consistency. The liquid limit in fine-grained soil refers to the moisture content at which the soil consistency shifts from plastic to viscous fluid. A third limit, known as the shrinkage limit, is a moisture content that indicates when the soil volume will not be lowered any further if the moisture content is dropped. As moisture content decreases, most fine-grained soils contract (shrink). The Plasticity Index or Plasticity Number, which is the numerical difference between the Plastic and Liquid limits, is another measure employed in soil research.
The mechanical properties of soils are also shown by the Atterberg limits. Note that the term “soil” refers to any unconsolidated material in the context of Atterberg limits (i.e. not bedrock). When the moisture content in a fine-grained soil climbs to the liquid limit, it can deform as a mass flow.
The method described below can be used to determine the moisture content of a soil in a variety of situations.
Gloves, Spatula, Drying Oven, Balance, Moisture Tin (Can)
The same process as described above is used to determine the moisture content of a sample. Below is a rundown of the steps.
1. Label and number a clean dry moisture tin. On a balance, weigh an empty dry can (tin weight).
2. Fill the moisture tin with a tiny amount of moist soil or sediment. On the balance, weigh the tin and a sample of moist soil or sediment. Make a weight record (wet soil and tin).
3. Place the moist sample in the moisture tin and dry it in the oven. Set the oven temperature to 105 degrees Celsius. Allow at least 24 hours for the sample to cook in the oven.
4. Turn the oven off and remove the moisture tin. Allow the tin to come to room temperature before removing it from the oven (may place in a desiccator). Weigh the moisture tin and the dry soil sample on the balance once they’ve both cooled down, and keep track of the weight (tin and dry soil).
5. Clean and empty the moisture tin. To ensure quality, repeat the operation.
Calculate the dry soil’s weight.
(Weight of Tin and Dry Soil) – (Weight of Tin and Dry Soil) – (Weight of Tin and Dry Soil) – (Weight of Tin and Dry (Weight of Tin)
2. Find out how much moisture there is.
Moisture Weight = (Weight of Tin + Weight of Moist Soil) – (Weight of Tin + Weight of Moist Soil) + (Weight of Tin + Weight of Mo (Weight of Tin and Dry Soil)
3. Find out how much moisture there is in the air.
(Moisture Weight)/(Weight of Dry Soil)*100 = Moisture Content (percentage)
Limits of the Atterberg
A Casagrande apparatus or a Cone Penetrometer can be used to determine Atterberg limits. The Casagrande Method will be applied in the lab.
Evaporating Dish, Grooving Tool with Gauge, Casagrande Device (liquid limit device).
Balance, Moisture Tins, a glass plate, a spatula, and some salt and pepper Drying Oven (at 105°C) after washing with distilled water
Figure 2: Liquid limit equipment required. The open cup is a Casagrande gadget. In the cup, a sample of damp soil is inserted and stressed (described below).
https://www.youtube.com/watch?app=desktop&v=GxXqqIuCfT0 Liquid Limit Procedure
1. Gather soil samples and filter them using a #40 standard sieve (0.42 mm). Medium sands and lower ones are allowed to pass through this sieve. Anything coarser than medium sand should be discarded. Dry, disaggregated samples are required (pulverized).
2. The sample should be between 100 and 125 grams in weight. Fill a ceramic plate with the sample. Mix the sample with a little distilled water until it resembles a smooth, consistently colored paste. It’s important to mix the dirt and water thoroughly. Dish should be covered.
3. Weigh three empty moisture tins with their lids and keep track of the weights, tin numbers, and lids.
4. Adjust the Casagrande equipment, if necessary, so that the cup’s drop height is 1 cm. The calibration block at the end of the grooving tool can be used to determine this distance. Adjust the cup’s base in relation to the worn region. Turn the crank at a two-drop-per-second speed.
5. Fill the cup of the Casagrande device with a part of the previously mixed soil, centered where the cup rests on the base (the cup can be removed from the apparatus at this point but attempt to fill the cup in place). To remove any air pockets, gently squeeze the moist dirt down. The sample should be patted to a horizontal surface and should be roughly 10 mm deep in the middle region (see Figure 2).
6. Cut a straight groove down the middle of the sample with the grooving tool. As you make the cut, keep the tool parallel to the surface (Figure 3). The soil sample should be sliced during the process.