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,[1] especially over soft ground. It also applies to the feet of a walking person or machine. Ground pressure is measured in pascals (Pa) which corresponds to the United States customary units unit of pounds per square inch (psi). Average ground pressure can be calculated using the standard formula for average pressure: P = F/A.[2] In an idealized 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 to 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.[3]

Increasing the size of the contact area on the ground (the footprint) in relation to the weight decreases the ground pressure. Ground pressure of 14 kPa (2 psi) or less is recommended for fragile ecosystems like marshes.[4] Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is often observed in activities like snowshoeing.

Example Ground Pressures

All examples are approximate, and will vary based on conditions

Hovercraft: 0.7 kPa (0.1 psi)

Human on Snowshoes: 3.5 kPa (0.5 psi)

Rubber-tracked ATV: 5.165 kPa (0.75 psi)

Diedrich D-50 - T2 Drilling rig: 26.2 kPa (3.8 psi)

Human male (1.8 meter tall, medium build): 55 kPa (8 psi)

M1 Abrams tank: 103 kPa (15 psi)

1993 Toyota 4Runner / Hilux Surf: 170 kPa (25 psi)

Adult horse (550 kg, 1250 lb): 170 kPa (25 psi)

Bagger 288 Excavation machine: 170 kPa (25 psi)

Passenger car: 205 kPa (30 psi)

Wheeled ATV: 13.8 kPa (2 psi)

Adult elephant: 240 kPa (35 psi)

Mountain bicycle: 245 kPa (40 psi)

Road racing bicycle: 620 kPa (90 psi)

Stiletto heel: 3,250 kPa (471 psi)

Note: Pressures for Man and Horse are for standing still. A walking human will exert more than double his standing pressure. A galloping horse will exert up to 3.5 MPa (500 psi). The ground pressure for a pneumatic tire is roughly equal to its inflation pressure.

See also

References

  1. ↑ Allen, Jim. Jeep 4 X 4 Performance Handbook. MotorBooks/MBI Publishing Company. p. 16. SBN 076030470X.
  2. ↑ Wenger, Karl F. (1984). Forestry Handbook. New York : Wiley. p. 499. ISBN 0-471-06227-8.
  3. ↑ J. William Thompson, Kim Sorvig (2000). Sustainable Landscape Construction: A Guide to Green Building Outdoors. Island Press. p. 51. ISBN 1-55963-646-7.
  4. ↑ "Page 4 of Management of small dock and piers, best management practices, May 2005 NOAA" (PDF).
  5. ↑ Wong, Jo Yung (2001). Theory of Ground Vehicles. New York : John Wiley,. ISBN 0-471-35461-9.


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