Ground pressure


Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. It also applies to the feet of a walking person or machine. Pressure is measured in the SI unit of pascals. Average ground pressure can be calculated using the standard formula for average pressure: P = F/''A''. In an idealised case, i.e. a static, uniform net force normal to level ground, this is simply the object's weight divided by contact area. The ground pressure of motorized vehicles is often compared with the ground pressure of a human foot, which can be 60 – 80 kPa while walking or as much as 13 MPa for a person in spike heels.
Increasing the size of the contact area on the ground in relation to the weight decreases the unit ground pressure. Ground pressure of 14 kPa or less is recommended for fragile ecosystems like marshes. Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is exemplified by use of equipment such as snowshoes.

Examples

All examples are approximate, and will vary based on conditions
ObjectGround pressure
Hovercraft0.70.1
Human on snowshoes3.50.5
Rubber-tracked ATV5.1650.75
Wheeled ATV13.82
Diedrich D-50 – T2 drilling rig26.23.8
Human male 558
Average human, flat shoes172.5
M1 Abrams tank10315
1993 Toyota 4Runner / Hilux Surf17025
Adult horse 17025
Bagger 288 excavation machine17025
Passenger car20530
Adult elephant24035
Mountain bicycle24540
Road racing bicycle62090
Commercial semi truck/Lorry793115
Stiletto heel3,250471

Note:
The pressures for average human and horse are for standing still position. A walking human will exert more than double his standing pressure. A galloping horse will exert up to 3.5 MPa. The ground pressure for a pneumatic tire is roughly equal to its inflation pressure.

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