Grade Work, Elevations, and Site Layout
The language of elevation
A benchmark is a fixed reference point of known elevation. A datum is the zero plane elevations are measured from. Existing grade is the ground as it is; design (finished) grade is the planned surface. The difference is cut (remove material) or fill (add material). Using the convention existing minus design, a positive result is a cut.
Grade stakes, hubs, and slope stakes carry the information to the field, usually with an offset distance and a cut or fill marked to a reference line. Stationing measures distance along a baseline in 100-foot stations: station 12+50 is 1,250 feet from the start.
Reading the plan
Plans include a plan view, a profile, and cross sections. Contour lines show shape; closely spaced contours mean steep ground. Spot elevations mark specific points, the north arrow fixes orientation, and the scale converts drawing distance to field distance. Contours pointing uphill in a stream channel form a V.
Tools and techniques
Rotary lasers, transits, total stations, and GPS machine control all establish or check grade. The operator's job is to check grade often, work to the stakes, and avoid over-cutting, which is expensive to backfill and recompact.
Traps in questions
Very common: mixing up cut and fill signs, treating station 12+50 as 1,250 stations, using slope percent instead of a ratio, and forgetting that a benchmark is fixed while a temporary hub is not.
Worked example
A point has existing elevation 104.2 ft and design elevation 101.8 ft. Cut/fill = 104.2 − 101.8 = 2.4 ft of cut. If a slope rises 6 ft over a 150-ft run, percent grade = (6 ÷ 150) × 100 = 4%.