In 1996, landowners Mark and Margaret Drury had a pond dug on their hillside
property. Although they anticipated some slippage on the uphill side of the pond, they were not prepared for the magnitude of the events that followed.
Mass wasting of soil into the pond occurred over time, requiring that it be re-dug in 2004 and the banks re-graded. Continued slippage of earth around the pond caused trees to lean. However, by 2008, the soil around the pond had ceased moving and the banks of the pond had stabilized.
The property with pond and buildings, showing the affected area upslope from the pond, is seen in Figure 1 below.
Imagine that you are a soils engineer asked to analyze the situation. You are too far away to visit the site, but photographs are provided. From the photographs, determine the amount of earth displaced over the 12 year period. Calculate the rate of displacement in cubic feet per year, assuming that displacement occurred smoothly during the 12 year period.
Prepare a report of the findings in standard lab report format. Use appropriate terminology from the textbook’s Chapter 4 and the corresponding PowerPoint to describe what happened. The report need not be any longer than one page of text.
The displaced earth left a volume shaped as a triangular prism. The volume of a triangular prism (see Figure 2) is V = (1/2)ABC
Figure 1. Property owned by the Drury family showing the pond and the area above the pond affected by displaced earth.
Figure 2. Triangular prism.
Comparing Figures 1 and 2, take C as the width of the affected volume, parallel to the pond’s edge on its upslope side (the line colored red).
Take B as the horizontal depth of the affected volume (the line colored blue), and A as the vertical height (the line colored yellow).
Determine the length in feet of the sides A, B, and C in Figure 1 by comparing those dimensions with the length of the trailer in the background on the left side (circled in red); assume the trailer is 10 ft long. You can use the drawing features of MS Word to compare the dimensions of the trailer and the colored lines.
The effect of the displacement on trees is illustrated by Figure 3.
Figure 3. Evidence of effect of displacement on trees near the pond.
Compare vertical trees in the background with the leaning tree in the
Case Study of Sculpturing Earth’s Surface Volume of displaced Earth:
Scale: Trailer in phot is 10 feet long.
Volume of displaced Earth :
V = 1/2 (ABC)
A = 9’
B = 32’
C = 60 ‘