California Surveyors Forums

so, I've been studying, and I can usually get the vertical curve through a point type problems.... but this one is kicking my butt... and I think I'm just doing something dumb... so please help... its a mission now as to why I can't solve it using the quad formula.

so:

L=2x+150
g1= 0.02
g2= -0.06

Elev@ station 14+25 ((75*-.02)+270.00)=268.50'
Elev@clear pipe is = 266.50' (elevation of curve at point)

y=2.00'

y=ax^2 a=(g2-g1)/2L

2= ((-.08)/(4x+300)) *x^2

8x+600=(-.08)x^2

.08x^2+8x+600=0

time for quad formula

(-b +/- sqrt(b^2-4ac))/2a

(-8 +/- sqrt(64-192))/ 0.16

can't have a neg square root....


I know there are other ways to solve it, and i have, but, i don't see what I'm doing wrong yet on this one, with this style.

thanks!

In your equation, your y-value of 2 should be negative, not positive. The methodology for vertical offsets for a vertical curve and for your equation is:

y is negative when the curve is a crest curve.
y is positive when the curve is a sag curve.

Check out page 3 of this pdf, this can explain it better.

http://www.pdhcenter.com/courses/l121/l121content.pdf

Son of a gun..... thats the issue.