Settling Soil

Read about how to complete a jar test in ‘The Trouble with Muck: Size’.

Throughout the project there have been discussions about the different lengths of time it takes to settle different soil types. In general sand settles the quickest followed by silt, clay, and lastly, muck. To demonstrate this process, jar tests were done with a mineral and muck soil sample. Jar tests are simply soil added to water and left to settle. The depth of the water to the top of the sediment layer was measured as 2 1/8”.

​The test was evaluated by taking pictures of the two jars at regular intervals (Figure 1). Calculations were done to predict when the various soils would settle out of the water, shown in Figure 2. As expected, the order in which they settled was sand first, then silt, clay, and finally muck. The sand settled so quickly it was impossible to get a picture with it still in suspension. The silt followed soon after and then took a period of time to fill in the spaces between the sand particles. Clay can be seen in suspension in Hour 6 but has cleared in Hour 24.

The calculations predicted that the muck would have settled in 22 days. While most of it cleared by the 21st day, the picture taken on the 100th day shows that there are still particles in suspension.

​Lastly, in both jars there is a layer of organic matter floating on the surface. These particles have made no downward movement through the time period.

The jars will continue to be monitored to determine whether the colour clears from the jar containing the muck soil.

Figure 1: The soil samples placed in Mason jars for the soil settling test and results over 100 days

Figure 2: Size and specific gravity of sand, silt, clay, and muck, and the average time to settle 2 1/8"