Free design toolUnsealed pavements · Working platforms

Mechanically stabilised pavement screening

Compare an unreinforced base with a Kontain BG geogrid section.

A transparent Giroud–Han calculation for unsealed roads, temporary access and working platforms over weak subgrades. Enter direct wheel loading and passes—this is not an ESA conversion or a sealed pavement design.

Design inputs

Load, traffic and ground

Wheel or dual-wheel-set loadkN

Typical guidance

1 kN equals 101.97 kg-force. A 40 kN wheel-set load is equivalent to about 4,079 kg static mass.
For an 80 kN axle with one dual-wheel set on each side, use 40 kN per dual-wheel set.
Use the maximum loaded operating condition. Apply any project-specific dynamic or impact allowance separately.

≈ 4,079 kg equivalent static supported massUse one wheel, or the combined load on a dual-wheel set.

Tyre contact pressurekPa

Typical guidance

Truck and bus load tables commonly span about 550–900 kPa (80–130 psi), depending on tyre size and actual axle load.
Off-road truck tyres are often around 400–700 kPa. Use the tyre or vehicle manufacturer's cold-pressure schedule.
Tracks have mean ground pressure, not tyre pressure. Caterpillar examples span roughly 25–90 kPa, but tracked plant is outside this circular tyre-contact method.

≈ 80 psiUse the loaded operating pressure, not a generic highway value.

Design passespasses

Typical guidance

5,000 and 10,000 are useful temporary-works screening cases; calculate actual axle passages wherever possible.
The original Giroud–Han paper says unpaved roads are typically designed for up to 100,000 axle passes.
For mixed axle groups, assess the governing axle load and repetitions rather than treating every vehicle as one identical pass.

Passes along the critical wheel path; not total site vehicle movements.

Lowest design subgrade CBR%

Typical guidance

0.5–1%: extremely weak; 1–2%: very weak; 2–3%: weak; 3–5%: fair for this screening method.
Use the lowest representative design value for the wettest credible condition, not an isolated favourable test.
The published method is limited to subgrade CBR below 5%.

Use the soaked, remoulded or otherwise representative design value.

Compacted aggregate CBR%

Typical guidance

15–20% is marginal/select material; 40% is a reasonable lower-strength granular screening case.
60% is a useful competent crushed-granular case. Current SA guidance uses a minimum soaked CBR of 60% for one PM3-like unsealed application.
80–100% may represent high-quality crushed base, but only use the tested project value. Grading and durability still control suitability.

Field compacted base-course value used in the method.

Allowable rut depthmm

Typical guidance

50 mm is the tighter limit in the published range; 75 mm is the Giroud–Han benchmark case.
100 mm is the upper method limit and may be operationally unacceptable for some vehicles or drainage conditions.
Select the serviceability limit before calculating—not the rut depth you expect crews to tolerate after failure.

The published method is limited to 50–100 mm.

Kontain BG productone layerWet, pumping, fine-grained or unstable formationApply a 300 mm construction-cover minimum and flag separation.

Project quantities and cost assumptions

Project or calculation referenceoptional

Lengthm

Length of the treated pavement.

Widthm

Average constructed width.

Compacted densityt/m³

Typical guidance

A preliminary value of 2.1 t/m³ gives 0.21 t/m² for each 100 mm compacted lift.
Use the project material's measured or supplier-advised compacted density where available.
Keep the density and supplier price on a consistent wet or dry mass basis.

100 mm = 0.210 t/m²Use the compacted mass basis matching the quoted A$/t rates.

Aggregate supplied to siteA$/t

Typical guidance

A$40/t is an editable delivered-to-site planning allowance, not a quoted market rate.
Adelaide retail PM2/20 has recently been listed at about A$51/t before project-specific delivery.
Bulk quarry rate, material specification, haul distance, order size and fuel adjustment can materially change this input.

≈ A$8.40/m² per 100 mmDelivered material only; keep placement and compaction separate.

Place, compact and moisture conditionA$/t

Typical guidance

A$24/t converts to A$5.04/m² per 100 mm at 2.1 t/m³, closely matching your A$5/m² estimate.
Use about A$10–A$18/t only for efficient, large continuous works with low mobilisation burden.
A$20–A$30/t is a reasonable preliminary band for ordinary civil works; small, wet, confined or remote work can exceed it.
Confirm whether grader, loader, roller, water cart, water, trimming, testing and mobilisation are included in the contractor rate.

≈ A$5.04/m² per 100 mmConstruction work only; excludes aggregate supply, excavation and disposal.

Geogrid supplied product rateA$/m²

Typical guidance

Use the delivered geogrid product price per purchased square metre.
The calculator applies the overlap and waste allowance to purchased product area.
Do not combine installation in this field—the laying allowance is entered separately.

Enter the actual delivered product rate; zero leaves total comparison incomplete.

Geogrid laying allowanceA$/treated m²

Typical guidance

Use A$1–A$2/m² as the normal separated laying allowance for straightforward rollout on a prepared formation.
Confirm whether alignment, cutting, pins, mobilisation, multiple small panels and difficult wet-ground access are included.
Keep material supply separate so the tool can calculate a useful break-even product price.

A$1.50/m² default when geogrid supply is priced separately.

Geogrid overlap and waste%

Typical guidance

Use project geometry, roll width and specified overlaps wherever known.
10% is a preliminary allowance for overlaps, edge trimming and offcuts—not a construction requirement.

Applied to purchased product area, not treated plan area.

Aggregate conversion at 2.10 t/m³A$8.40 supply + A$5.04 construction = A$13.44/m² per 100 mmEach 100 mm compacted lift uses approximately 0.210 t/m².

Calculated comparison

525 mm without gridvs300 mm with BG40

Adopted thickness effect225 mm less43% indicative reduction

Selected gridBG40one layer at base/subgrade interface

Aggregate volume change135 m³ less600 m² treated area

Initial cost comparisonAdd grid ratebreak-even supply rate A$26.13/m²

Unreinforced525 mm

Compacted granular base525 mm

Design subgrade

Mechanically stabilised300 mm

Compacted granular base300 mm

BG40 geogrid

Design subgrade

Editable commercial comparison

Initial pavement cost

Without geogridA$42,336aggregate supply, placement, compaction and moisture conditioning

With BG40Product rate requiredaggregate supply/construction + grid supply + A$1.50/m² laying

Break-even product rateA$26.13/m²maximum delivered grid price at 10% allowance

Cost itemWithout gridWith grid

Aggregate supply (A$40.00/t · A$8.40/m²/100 mm)A$26,460A$15,120

Place, compact and condition (A$24.00/t · A$5.04/m²/100 mm)A$15,876A$9,072

Geogrid supply (660 m² purchased)—Enter rate

Geogrid laying—A$900

Screening estimate only. It excludes excavation, spoil disposal, geotextile separation, drainage and programme effects. Include water, mobilisation and testing in the aggregate construction rate where applicable. Reduced excavation may add further value but is deliberately not counted.

Preliminary layer schedule

Mechanically stabilised option

Compacted granular baseCBR 60% · adopted 300 mm

BG40 biaxial PP geogridone layer at base/subgrade interface · nominal aperture 33 mm

Separation and filtration layeruse a compatible nonwoven geotextile or approved composite

Prepared design subgradelowest representative CBR 1% · proof and accept before placement

Checks requiring attention

BG40 is only a preliminary starting class below CBR 2%. Review first-lift thickness, plant access, staged construction and ground treatment.
BG40 publishes J = 0.98 m-N/degree. The calculation uses J = 0.75 because the published Giroud–Han calibration requires J below 0.8.

Calculation audit trail

Design basis and adoption logic

Document statusAutomated preliminary screening output

This output is not certified unless it is accompanied by a separate, expressly signed pavement design certification.

Project referenceNot entered

Method and equationGiroud–Han (2004), Part II, Eq. 17

Model scopeUnsealed road or working platform

Controlling mechanism assumedSubgrade bearing and rutting

Design inputAdopted valueUse in calculation

Wheel or dual-wheel-set load, P40 kNEquivalent tyre contact radius

Tyre contact pressure, p550 kPaCircular contact area approximation

Design axle passes, N5,000Logarithmic traffic deterioration term

Subgrade / aggregate CBR1% / 60%Subgrade strength and limited modulus ratio

Allowable rut depth, s75 mmBearing-capacity mobilisation

Selected geogrid / layer positionBG40 / one layerAt base–subgrade interface

Aperture stability, J0.98 published / 0.75 usedReinforced deterioration coefficient

Formation conditionUnstable / wet condition selected300 mm minimum cover

Convert wheel load and pressure to contact radius

The equivalent circular tyre radius is r = √[P/(πp)]. For these inputs, r = 152.2 mm.

Limit the base-to-subgrade modulus ratio

R_E = min[3.48 CBR_bc^0.3 / CBR_sg, 5], then f_E = 1 + 0.204(R_E − 1). The calculated limited ratio is 5.000.

Iteratively solve Giroud–Han Equation 17

Thickness appears on both sides of the equation through the traffic deterioration and bearing-mobilisation terms. The control uses J = 0 and N_c = 3.14; the geogrid case uses J = 0.75 and N_c = 5.71.

Apply serviceability and construction overrides

Raw calculated thicknesses are 503.7 mm without grid and 111.6 mm with grid. The tool then checks the rut-depth minimum, enforces the 300 mm construction-cover minimum and rounds adopted thickness up to the next 25 mm.

Raw equation result503.7 mmunreinforced

Raw equation result111.6 mmBG40 screening case

Adopted result525 / 300 mmwithout / with geogrid

Bearing mobilisation, m0.178 / 0.860without / with geogrid

Optional next step

Project-specific pavement design certification is available.

Certification requires review of the project ground model, representative design CBR, traffic and wheel loads, drainage, aggregate source and test data, geogrid conformity, construction sequence and applicable client or authority requirements.

Request certification review ↗

Uncertified-output limitations and reliance

This automated result is a preliminary comparison only. It is not engineering advice, a certified pavement design, a specification, a tender recommendation or a construction instruction.
The user is responsible for the accuracy, completeness and representativeness of all inputs. The tool does not independently verify site investigation, seasonal moisture, local weak zones, drainage, aggregate grading or durability, construction damage, wheel wander, dynamic effects, maintenance or statutory and authority requirements.
The geogrid comparison uses the published Giroud–Han calibration as a screening relationship. Kontain BG product properties are not product-specific trafficking calibration. No guaranteed thickness reduction, design life, rut performance, cost saving or fitness for a particular project is stated or implied.
Do not rely on this output for procurement, tender, certification or construction unless the complete pavement has been reviewed and a separate signed certification or approved project design has been issued.
To the maximum extent permitted by law, Kontain excludes liability for loss, damage, cost, delay or consequential or economic loss arising from use of, or reliance on, an uncertified output. Where liability cannot lawfully be excluded, it is limited, where permitted, to resupplying the relevant service or paying the reasonable cost of resupply. Nothing here excludes rights or liabilities that cannot lawfully be excluded.

Reference: J.P. Giroud and J. Han (2004), “Design Method for Geogrid-Reinforced Unpaved Roads. II: Calibration and Applications”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 130(8), pp. 787–797, Equation 17. Open source paper ↗

Method traceability

What the tool is doing—and what it is not claiming.

Method

Giroud–Han (2004)

Iterative base-thickness calculation using wheel load, tyre pressure, passes, rut limit, base and subgrade CBR, bearing capacity and aperture stability modulus.

Open published paper ↗

Benchmark

504 mm / 181 mm

The implementation reproduces the published example at 40 kN, 550 kPa, 5,000 passes, CBR 1, base CBR 15 and J = 0.65.

Product boundary

BG data is not yet a trafficking calibration

The authors later clarified that the calibrated J relationship applied to the specific biaxial grids used in the original testing. Kontain BG results must remain screening outputs until matched performance evidence is available.

Read calibration guidance ↗

Construction

Minimum cover overrides the raw equation

The adopted reinforced thickness is rounded up to 25 mm and cannot be less than 200 mm on firm formation or 300 mm where CBR ≤2% or the formation is unstable.

Open Kontain installation guide ↗

Input guidance

Loads, pressures and CBR need project values

Truck inflation schedules commonly cover 550–900 kPa. Tracked plant uses mean ground pressure and is not directly represented by the circular tyre-contact model. Current SA guidance provides a useful CBR 60 reference for competent PM3-like material in one unsealed application.

Open truck load-pressure table ↗Open SA pavement guidance ↗

Cost benchmark

Material and construction are priced separately

The editable defaults are A$40/t for aggregate delivered to site and A$24/t to place, compact and moisture condition it. At 2.1 t/m³ this is A$8.40 + A$5.04 = A$13.44/m² per 100 mm. Public plant rates and recent programme-level pavement costs support this as a sensible planning case, but project scale, quarry distance, access and testing can move it materially.

Open City of Gosnells cost appendix ↗Open current public plant rates ↗Open Adelaide PM2/20 retail reference ↗

Kontain BG inputs used

Published typical product data

Open BG Series TDS ↗

Product	Ultimate tensile	Strength at 2%	Nominal aperture	Published J	J used in tool
BG20	20 kN/m	7 kN/m	35 × 35 mm	0.50 m-N/degree	0.50 m-N/degree
BG30	30 kN/m	10.5 kN/m	34 × 34 mm	0.75 m-N/degree	0.75 m-N/degree
BG40	40 kN/m	14 kN/m	33 × 33 mm	0.98 m-N/degree	0.75 m-N/degree (method cap)

Values are typical published data and must be confirmed against the exact supplied product. Ultimate tensile strength is not used to calculate thickness reduction.