Earthwork Question from Caltrans Workbook

[divs]

Hi,

I have a question about an earthwork problem from Chapter 8 of the Clastrans workbook.

http://www.dot.ca.gov/hq/row/landsurveys/LSITWorkbook/08.pdf

The question and the figure for the solution are attached. How are 4 circled values calculated? Figure.pdf

 

[ptatohed]

divs,

Those red circles are the locations where the proposed template cross-section daylights with the existing ground. The top number is the elevation and the bottom number is the horizontal distance from CL (positive = rt, negative = lt). For instance, in looking at the left side of the 36+00 cross section, if you are at 87|-27 (El = 87 at 27' left of CL) and go up at a 2:1 slope, your daylight (or catch point) will be at 92.1|-36 (El = 92.1 at 36' left of CL).

The only way to get the exact horizontal and vertical numeric values of the daylight location is to calculate the intersection of the two lines (two equations, two unknowns).

For some reason, I get a catch point of El = 92.31 at 37.61' LT for the left side which doesn't match the solution's catch point but I agree with the right side: 87 + (1/2)(x) = y and 90.0 - 0.0286(x+12) = y. El = 89.51 at 32.03' RT (Sta 36+00).

Does that help?

 

[IlPadrino]

It looks like to me there are some errors in the solution. For example, the elevation at the bottom of the ditch on the right at sta 35+50 isn't 87! And you can easily verity the catch points by using the slope from the lower points - they don't all work.

 

[divs]

Thank you both! Yes, there's a lot of errors in the solution which kinda confused me.