Measuring Soil Cracks
The first step is picking axes along which the cracking can be measured. Three axes are noted in the diagram to the right. In the following images, a ruler is laid over the dish along each axes, and the cracking is measured.
The total inside diameter (width) of the petri dish is 52 mm. Summing the crack widths along this vector (the edge of the ruler) from the top right , reveals cracks of 1 mm, 1 mm, 1 mm, 4 mm, 4 mm, and 1 mm for a total of 12 mm of cracks.
Summing the crack widths along this vector (the edge of the ruler) from the far right , reveals cracks of 1 mm, 1 mm, 2 mm, 2 mm, and 6 mm for a total of 12 mm of cracks.
Summing the crack widths along this vector (the edge of the ruler) from the bottom right , reveals cracks of 0.5 mm, 0.5 mm, 2 mm, and 5 mm for a total of 8 mm of cracks.
The mean horizontal cracking in this dish is (12 mm + 12 mm + 8 mm) / 3 = 10.7 mm.
The percent shrinkage is
(10.7 mm / 52 mm) 100 = 20.6%
The dish height is 9 mm, and the saturated paste of bentonite filled the dish. The thickness (height) of the soil is now 3 mm. The vertical shrinkage is
[(9 mm - 3 mm) / 9 mm] 100 = 66.7%
Return to Unit 2