Construction Surveying
Construction surveying tests plan reading, stakeout geometry, elevation control, and measurement for payment on Michigan projects, where MDOT Standard Specifications and project special provisions govern.
Plans, stationing, and stakeout
Alignments are described by station (100-ft stations, for example 12+35.50) and offset, with offsets signed left or right of the baseline. Set horizontal control from the plan coordinates, then compute cut or fill as design elevation minus existing ground. Slope stakes belong where the side-slope plane intersects existing ground; check the catch point by computation, not by eye.
Elevation control
Use the height-of-instrument method: HI = bench mark elevation + backsight; ground elevation = HI − foresight. Close every loop on a known bench mark. Third-order closure limits are commonly expressed as a constant times the square root of the loop length in miles (for example 0.05 ft × √miles), but the project's stated tolerance always controls.
Machine control and as-builts
Verify the model and local calibration against a known point before trusting automated grading. As-built shots document actual location and elevation for pay quantities and record drawings; measure quantities from approved cross sections.
Worked example
BM 100.00, BS 4.12 gives HI 104.12; FS 3.85 gives ground 100.27. Next setup: BS 2.40 gives HI 102.67; FS 5.10 gives ground 97.57. A four-setup loop closes 0.04 ft over 1.6 miles. Allowable = 0.05√1.6 = 0.063 ft, so the loop is accepted and the misclosure is distributed.
Traps
Using a foresight as a backsight; mismatched vertical datum between plans and field; ignoring curvature and refraction on long shots; certifying quantities from unverified cross sections; reversing cut and fill signs.