Slope staking locates the catch point — where the cut or fill slope meets existing terrain — and drives a stake there to mark the earthwork limit. Fill areas: offset = half-width + (fill depth × fill slope ratio). Cut areas: offset = half-width + ditch width + (cut depth × cut slope ratio). The procedure is iterative: estimate an offset, measure the ground elevation there, recalculate, and adjust until design elevation at that offset matches existing ground.
What Is a Slope Stake?
A road cross-section shows the roadway at a specific elevation with slopes extending from the edge to the original terrain. The catch point is where that slope meets existing ground — the earthwork limit. Stakes driven at catch points mark the grading limits for equipment operators and establish the payment quantities for the earthwork bid. Wrong catch points mean wrong quantities.
Key Terms
- Catch point: Where cut or fill slope meets existing terrain. Where the stake goes.
- Horizontal offset: Distance from road centerline to catch point.
- Design slope ratio: Horizontal run per vertical foot (2:1 = 2 ft horizontal per 1 ft vertical).
- Half-width: Distance from centerline to roadway edge.
Slope Stake Equations
Example: half-width = 20 ft, fill depth = 6.0 ft, slope 2:1
Offset = 20 + (6.0 × 2) = 32 ft from CL
Cut: Offset = half-width + ditch width + (cut depth × cut slope ratio)
Example: half-width = 20 ft, ditch = 6 ft, cut depth = 4.5 ft, slope 2:1
Offset = 20 + 6 + (4.5 × 2) = 35 ft from CL
Field Procedure: The Trial Method
Slope staking is iterative: the offset depends on the fill/cut depth, which depends on the catch point, which depends on the offset. Converge through trial and error.
- Estimate a trial offset based on experience or rough cross-section from plans.
- Take a rod shot at the trial offset to get the existing ground elevation.
- Calculate the design elevation at that offset (work out from the subgrade CL elevation).
- If ground elevation equals design elevation at the trial offset — that is the catch point. If not, adjust offset and repeat.
- Drive the slope stake. Mark: station (STA 12+50), side (LT/RT), cut/fill depth, and horizontal offset.
Slope Stake Markings
- Station number (STA 12+50)
- Side: LT or RT
- Cut or fill depth: “C 4.5” or “F 6.0”
- Horizontal offset: “35 RT”
Common Problems
- Variable terrain requires more trials: Two to three iterations is normal on irregular slopes. A quick estimate approach leads to stakes 5+ feet off the catch point.
- Catch point outside ROW: Mark the ROW limit stake and note it. The designer needs to know — additional ROW or a design change may be required.
See also: Cut and Fill Calculations for Site Grading.