Apron Pavement Thickness Calculator

Calculator

Inputs

Project name

Used in exports and result summary.

Prepared by

Free text label for reporting.

Unit system

Switch input/output units without manual conversion.

Pavement type

Choose a method suitable for your apron concept.

Design wheel load (kN)

Single-wheel design load used for thickness sizing.

Tire pressure (MPa)

Used to estimate contact radius for rigid checks.

Traffic input

Preset uses typical screening repetitions.

Traffic preset

Ignored when custom repetitions is selected.

Custom repetitions (passes)

Used when traffic input is set to custom.

Reliability (%)

Higher reliability increases thickness slightly.

Drainage condition

Poor drainage increases required thickness.

Safety factor

Applied to both flexible and rigid sizing.

Rounding increment

Rounds layer thickness for constructability.

Subgrade CBR (%)

Used for flexible option thickness estimate.

k (subgrade reaction) (MN/m3)

Support stiffness for rigid slab iteration.

Concrete flexural strength (MPa)

Used to compute allowable stress.

Concrete modulus (GPa)

Elastic modulus for relative stiffness.

Poisson ratio

Typical range 0.12-0.20.

Load transfer efficiency (%)

Higher values reduce edge stress.

Reset

Tip: For rapid checks, start with the preset traffic level, then refine using custom repetitions and measured subgrade parameters.

Formula used

Calculation approach

This tool provides a practical sizing screen for apron pavement thickness using two selectable paths: flexible (surface + base) and rigid (slab + subbase).

Flexible option (CBR-based screening)

Total thickness is estimated using an empirical relationship that increases with wheel load and traffic, and decreases with stronger subgrade. Reliability, drainage, and safety factors are applied.

T_total(mm) = 25 x sqrt(P) x (log10(N)+1)^0.25 / CBR^0.35 x Fd x Fr x SF

P = wheel load (kN), N = repetitions, CBR = subgrade strength (%), Fd = drainage factor, Fr = reliability factor, SF = safety factor.

Layers are split for constructability: surface ~ 35% (minimum 75 mm), base ~ 65% (minimum 100 mm), then rounded to the selected increment.

Rigid option (simplified edge stress iteration)

The rigid check iterates slab thickness until computed edge stress is below allowable stress. Contact radius is estimated from wheel load and tire pressure, and relative stiffness uses the modulus of subgrade reaction.

a = sqrt(P / (pi*p))
l = [(E h^3) / (12(1-nu^2)k)]^0.25
sigma_edge = (0.572 P / h^2) x (1 + 0.54(a/l)) x Flte
sigma_allow = (MR x SR) / SF

P = wheel load (N), p = tire pressure (Pa), h = slab thickness (m), E = concrete modulus, nu = Poisson ratio, k = subgrade reaction, MR = flexural strength, SR = stress ratio allowance (based on N), Flte reduces stress when load transfer is higher.

A conservative subbase suggestion is added based on k to improve support and uniformity.

How to use

Workflow

Select a unit system that matches your available data.
Choose flexible for layered asphalt/base, or rigid for concrete slab design.
Enter wheel load and tire pressure from your governing equipment/aircraft.
Set traffic using a preset level or your own repetitions estimate.
Provide subgrade strength (CBR for flexible, k for rigid) and material properties.
Press Submit to view results above the form under the header.
Use Download CSV or Download PDF to attach results to reports.

Example data table

Sample inputs and outputs

Case	Type	Wheel load	Tire pressure	Traffic	Subgrade	Recommended thickness
1	Flexible	80 kN	1.2 MPa	Heavy preset	CBR 8%	Surface 160 mm + Base 300 mm (Total 460 mm)
2	Rigid	110 kN	1.4 MPa	500,000 passes	k 60 MN/m3	Slab 260 mm + Subbase 150 mm (Total 410 mm)
3	Flexible	60 kN	1.0 MPa	Medium preset	CBR 12%	Surface 120 mm + Base 220 mm (Total 340 mm)

Examples are illustrative. Use your own governing loads, traffic, and measured subgrade values for estimates.

Flexible option (CBR-based screening)

Rigid option (simplified edge stress iteration)

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