A sanitary line must fall at 1.2 percent over a 350 ft horizontal run. What invert drop should be shown between the two structures?
Correct Answer
A) 4.2 ft
A 1.2 percent slope is 0.012 ft/ft. Drop is 350 x 0.012 = 4.2 ft. Other choices use 1.0 percent, round incorrectly, or convert percent too low.
Why This Is the Correct Answer
A 1.2 percent slope is 0.012 ft/ft. Drop is 350 x 0.012 = 4.2 ft. Other choices use 1.0 percent, round incorrectly, or convert percent too low.
Why the Other Options Are Wrong
Option B: 3.5 ft
pipe slope, choice a: 3.5 ft is wrong because 3.5 ft implies about 1 percent fall over 350 ft; the stated slope is the one used in.
Option C: 3.8 ft
pipe slope, choice b: 3.8 ft implies about 1.09 percent fall over 350 ft; the stated slope is the one used in.
Option D: 4.0 ft
pipe slope, choice c: 4.0 ft implies about 1.14 percent fall over 350 ft; the stated slope is the one used in.
Memory Technique
Picture a warning sign labeled pipe slope: finish every operation before accepting 4.2 ft.
Reference Hint
Open Pipe and Excavation Contracting, 2011; use the index entry or section for "Pipe grade and invert calculation" to confirm that A 1.2 percent slope is 0.012 ft/ft.
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