Vehicle cone index for one pass (VCI₁)

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

Ref: TER-28
Rev: v1
Field: Terramechanics and off-road mobility
Result: VCI₁ [psi]

V C I_{1} = 0.096 M M P

VCI₁ = 0.096 MMP is the cone index in psi that the soil must have to carry a tracked vehicle through a single pass, from its mean maximum pressure in kPa. The coefficient includes the unit conversion, so enter MMP in kPa and read psi. Compare against the remoulded cone index in psi for the corresponding pass count and calibration. Do not compare VCI₅₀ directly with a single-pass criterion as if they measured the same thing. MMP values of 301 and about 305 kPa appear in the lecture; the figure used here is 304.7 kPa.

Cone index in psi that a soil must have to carry a tracked vehicle through a single pass, estimated from its mean maximum pressure in kPa. The coefficient already contains the unit conversion.

Calculator

Solve for

VCI₁Vehicle cone index, one passComputed

psi

MMPMean maximum pressure

kPa

100700

VCI₁ in kPa201.7 kPa
VCI₅₀ for comparison (50 passes)82.27 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, one pass (psi) current value 29.25 psi

MMPMean maximum pressureKey driver

9.667.2

An MMP of 304.7 kPa needs a soil cone index of 29.25 psi (201.7 kPa) for one pass. A remoulded cone index of 240 kPa is 34.8 psi, enough for one pass but short of the 50-pass requirement of 82.27 psi.
Because the relation is linear in MMP, reducing MMP by 10 % lowers the requirement by 10 %: from 29.25 to 26.33 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	9.6	67.2	57.6	+10%	+10 %

Sweep of Mean maximum pressure

Mean maximum pressure (kPa)	Vehicle cone index, one pass (psi)
100	9.6
175	16.8
250	24
325	31.2
400	38.4
475	45.6
550	52.8
625	60
700	67.2

Sweep one variable

Vary

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

Variables and how each one contributes

VCI₁

Vehicle cone index, one pass

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 VCI₁ in proportion. Raising it by 10 % (to 335.2) moves the result by +10 %, from 29.25 to 32.18 psi.

Worked example with the values above

Multiply the pressure by the coefficient: 0.096 × 304.7.
VCI₁ = 29.25 psi.
In kPa that is 201.7 kPa (multiply by 6.894757).

Assumptions and limits

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

Common mistakes

Comparing the result in psi with a soil strength in kPa.
Applying a one-pass VCI to a multi-pass mission.

Statistics and uncertainty

The coefficient comes from fitted data, with scatter of order ±15 %, so a vehicle within 10 % of the soil strength is a toss-up. Use VCI as a screening tool and check with a trial crossing where the margin is small.

Where it is used

Go or no-go screening of a tracked vehicle for a single crossing.
Comparing the result with the remoulded cone index in psi.

Maths you need

Mean maximum pressure: peak pressure under road wheels
Unit conversion: 1 psi = 6.894757 kPa

Related formulas

Practise this formula