Grading shapes the roadbed to the right line, level and cross-slope before any surface goes on: stake the centreline, cut the high spots, fill the low ones, compact in layers, and check with a string and a water level. Grade is rise divided by run, so a 3% grade rises 30 cm in every 10 m of road. Do the earthwork in dry weather, which the parent calls the best time for major construction.
Part of Road Construction Basics
Shaping the ground under a road to a planned line and slope with shovels, picks, string and a water level.
Grading Sets The Road’s Shape Before The Surface Is Laid
A surface laid on a badly shaped bed fails sooner. Grading has three jobs: put the road on the line you marked, bring it to the planned height, and give it the slope that carries water off. The parent article lists the tools, the cut and fill technique, and the compaction methods; this page puts them in sequence.
Grade is measured as rise over run. A 5% grade rises 5 m in 100 m, or 1.0 m in 20 m. Ratios such as 1:20 mean the same thing: 1 m of rise in 20 m of run. See Grade Calculation for the tables.
What You Need
- The tools — see Essential Tools.
- Stakes and string to hold alignment and height.
- A water level, a clear tube filled with water. See Water Level.
- A plan — start height, grade, and width.
Method: The Order Of Earthwork
Step 1: Stake the line and the heights Drive stakes along the centreline every 5 or 10 m. Compute the design height at each: start height plus distance times grade.
Step 2: Read the ground against the design At each stake, subtract the design height from the ground height. Positive means cut, negative means fill.
Step 3: Cut high spots, fill low ones Use cut material for the fill where you can. On a hillside see Cut & Fill Technique.
Step 4: Compact each layer See Compaction Methods.
Step 5: Crown and ditch Shape the cross-slope and dig the ditches. See Road Crown & Camber and Side Ditches.
Worked Example: Staking 60 m At A 3% Grade
Inputs: start height 100.00 m; grade 3%, so 0.03 × 10 m = 0.30 m of rise per 10 m station. The ground heights are assumed readings for illustration.
| Station | Design height | Ground height | Ground − design | Action |
|---|---|---|---|---|
| 0 m | 100.00 | 100.00 | 0.00 | none |
| 10 m | 100.30 | 100.20 | −0.10 | fill 10 cm |
| 20 m | 100.60 | 100.75 | +0.15 | cut 15 cm |
| 30 m | 100.90 | 100.90 | 0.00 | none |
| 40 m | 101.20 | 101.05 | −0.15 | fill 15 cm |
| 50 m | 101.50 | 101.65 | +0.15 | cut 15 cm |
| 60 m | 101.80 | 101.70 | −0.10 | fill 10 cm |
Cuts: 15 + 15 = 30 cm at two stations. Fills: 10 + 15 + 10 = 35 cm at three. The road is close to balanced, so little material needs to be hauled in or out. The total rise is 101.80 − 100.00 = 1.80 m over 60 m, which is 1.80 / 60 = 3%.
Common Mistakes
- Staking too far apart — bumps between stakes go unseen. Use 5 or 10 m.
- Using the ground as the grade — a road that follows every hump has no grade. Set heights from the design.
- Skipping compaction between layers — fill settles and ruts form. See the parent.
- Grading in wet weather — the parent says dry ground is easier to work and summer is the best time for major construction.
Safety
Digging tools and trenches
Picks, mattocks and shovels cause cuts and crushed toes. Keep a full swing’s length between workers, wear boots, and never dig under a bank that overhangs. Stop work if a cut face cracks or the ground is saturated.
What’s Next
- Learn next: Essential Tools — what to bring
- Combine with: Cut & Fill Technique — grading on a slope