Inputs
Enter values and calculate the approach slab length
Fields adapt to screen size (3/2/1 columns).
Formula used
How the calculator determines approach slab length
This tool compares three practical ways to size an approach slab transition. It computes each method, then selects the largest value as a conservative governing length.
- Δh = H + s where H is embankment height and s is settlement allowance.
- Factor method: L₁ = k × H (choose k based on your standard).
- Grade method: L₂ = Δh / (g/100) where g is allowable grade change in percent.
- Ratio method: L₃ = Δh × n where n is the horizontal ratio in 1:n.
- Governing length: L = max(L₁, L₂, L₃, Lmin) when a minimum length is applied.
How to use
Steps for a clean, review-ready result
- Select your units, then enter embankment height and settlement allowance.
- Set either an allowable grade (%) or a transition ratio (1:n), or both.
- Choose factor k to reflect your typical practice.
- Enable the minimum length if your standard requires it.
- Optionally add width and thickness to estimate concrete volume.
- Press Submit to view results, then export CSV or PDF.
Example data table
Sample inputs and typical outputs
| Case | H (m) | Settlement (mm) | Grade (%) | Ratio (1:n) | k | Governing length (m) | Concrete volume (m³) |
|---|---|---|---|---|---|---|---|
| A | 2.0 | 25 | 2.0 | 30 | 2.0 | 30.75 | 21.525 |
| B | 1.2 | 15 | 3.0 | 20 | 2.5 | 24.30 | 13.608 |
| C | 3.5 | 40 | 1.5 | 35 | 1.8 | 124.60 | 87.220 |
Example assumes width = 3.5 m and thickness = 200 mm for volume.