Practice Quiz

Surveying FS

Category - Plane Survey Calc

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What is the elevation of the point of vertical tangency for an equal-tangent sag vertical curve with the following given information?

G1 = -4%, G2 = +2%, L= 400ft, PVCSta = 100+00, PVCElev = 100.00 ft
  1. 96 ft
  2. 104 ft
  3. 128 ft
  4. None of the above
Explanation
Answer: A - the elevation of the point of vertical tangency for an equal-tangent sag vertical curve is 96 ft.

Solution

Use the general parabolic formula for a vertical curve.
y = ax2 + bx + c

Where a = (G2 - G1)/2 = (0.02 -(-0.04))/2(400) = 0.00008

x = curve length = L = 400 ft

b = G1= 0.04

c = PVC elevation = 100 ft

y = 0.00008 (400)2 + (-0.04)(400) + 100 = 12 - 16 + 100 = 96 ft.
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