Vehicle cone index for 50 passes (VCI₅₀)

Cone index in psi that a soil must have to carry a tracked vehicle through fifty passes, estimated from its mean maximum pressure in kPa.

Ref: TER-29
Rev: v1
Field: Terramechanics and off-road mobility
Result: VCI₅₀ [psi]

V C I_{50} = 0.27 M M P

VCI₅₀ = 0.27 MMP is the cone index in psi that the soil must have to carry a tracked vehicle through fifty passes, from its mean maximum pressure in kPa. Repeated passes remould the soil, so the requirement is much higher than the one-pass value: the coefficient 0.27 is 2.8 times 0.096. The coefficient includes the unit conversion, so enter MMP in kPa and read psi. Do not compare VCI₅₀ directly with a single-pass criterion as if they measured the same requirement.

Cone index in psi that a soil must have to carry a tracked vehicle through fifty passes, estimated from its mean maximum pressure in kPa. Many passes churn the soil, so the requirement is much higher than for one.

Calculator

Solve for

VCI₅₀Vehicle cone index, 50 passesComputed

psi

MMPMean maximum pressure

kPa

100700

VCI₅₀ in kPa567.2 kPa
VCI₁ for comparison (one pass)29.25 psi

What drives the result

Each variable is moved across its typical range while the others stay at the values above. The longest bar is the key driver.

Vehicle cone index, 50 passes (psi) current value 82.27 psi

MMPMean maximum pressureKey driver

27189

An MMP of 304.7 kPa needs 82.27 psi (567.2 kPa) of soil strength to survive fifty passes, 2.81 times the one-pass requirement of 29.25 psi. A soil that comfortably carries one vehicle can fail a long convoy.
Reducing MMP by 10 % lowers the requirement by 10 %, from 82.27 to 74.04 psi.

Chart data as tables

Ranked variables

Variable	Typical range	Lowest result	Highest result	Swing (psi)	Local step	Change in result
MMP Mean maximum pressure	100 to 700 kPa	27	189	162	+10%	+10 %

Sweep of Mean maximum pressure

Mean maximum pressure (kPa)	Vehicle cone index, 50 passes (psi)
100	27
175	47.25
250	67.5
325	87.75
400	108
475	128.3
550	148.5
625	168.8
700	189

Sweep one variable

Vary

Vehicle cone index, 50 passes (psi)Hover, touch, or use the arrow keys on the chart

Variables and how each one contributes

VCI₅₀

Vehicle cone index, 50 passes

Result · psi

What the equation gives you. Everything else feeds it.

MMP

Mean maximum pressure

kPa · typical 100 to 700

The mean maximum pressure of the vehicle, in kPa (see the mean maximum pressure entry). Raises VCI₅₀ in proportion. Raising it by 10 % (to 335.2) moves the result by +10 %, from 82.27 to 90.5 psi.

Worked example with the values above

Multiply the pressure by the coefficient: 0.27 × 304.7.
VCI₅₀ = 82.27 psi.
In kPa that is 567.2 kPa. The one-pass requirement is 29.25 psi.

Assumptions and limits

A tracked vehicle on fine-grained soil, fifty passes.
MMP in kPa; result in psi.

Common mistakes

Comparing the result in psi with a soil strength in kPa.
Using a single-pass criterion for a long convoy.

Statistics and uncertainty

The coefficient comes from fitted data with scatter of order ±15 %. The pass count enters only through the choice of coefficient, so the 50-pass value is a step, not a continuous scale. Check intermediate pass counts with a calibrated method.

Where it is used

Judging whether a route can survive repeated traffic, not just the first vehicle.
Setting traffic limits on soft ground.

Maths you need

Mean maximum pressure: peak pressure under road wheels
Remoulding: soil weakening under repeated traffic

Related formulas

Practise this formula