Example 6.5 Chapter 6, REZA surveying book.
This example is about cross section leveling and estimating the earthwork volume. What I don't understand is how is a cut of 4 ft appearing above the zero foot line of the roadway??? If it's a cut shouldn't it go below the zero foot line? This is looking more like a 4ft fill than a cut!! Please advise. For the record, I have a difficult time understanding cross-section leveling in the first place.
It you were standing at the center-line stake at Sta 10+25, and it reads C6.0/0 you are 6' above the proposed finished sub-grade of the road. The road builder has to cut 6' at center-line. If you are at the left slope stake C4.0/16, you are standing 4' above and 16' horizontal from the proposed center-line. At the right slope stake, C12.0/28 you are 12' above and 28' horizontal from the proposed center-line.
You can use the right and left stakes for reference in building the road to determine the road is cut to grade.
On thing maybe to notice is this particular section of road is generally called "through cut".
I can never remember the coordinate method off the top of my head, so on these problems I usually roughly draw and label the areas like the example, but also sketch in the triangles on each edge of the road. I divide the gross area into 2 trapezoids, compute their areas and subtract the areas of the 2 triangles.
Area at Sta 10+25 = 16(4+6)/2 +28(6+12)/2 -0.5(4)(6) -0.5(12)(18) =332-120 = 212 sq ft
Area at Sta 11+25 = 13(2+3)/2 +22(3+8)/2 -0.5(2)(3) -0.5(8)(12) =153.5-51 = 102.5 sq ft
Average end area 10+25 to 11+25 =0.5(212+102.5)100/27 =582.4 cubic yards (bank measure)
Also if you do an internet search for cross section leveling , you can come up with a lot of info on construction staking and volume calculation.
Problems like these also come up sometimes in the morning construction part of the PE test, too.
Good Luck.
