Coefficient of friction of soft soils?

Topics related to Vehicle Specifications, Vehicle Acceleration Tests, Vehicle Braking Tests
MSI
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Coefficient of friction of soft soils?

Post by MSI »

For historical information, check out
  • "Roadside Design for Safety" by Stonex (1960). It may be in other Stonex papers (some published through SAE since they include a lot of history on crash safety research). In the 1960 paper he towed vehicles sideways through wet and dry sod. In the Stonex tests towing the vehicle sideways produced coefficients of friction > 1 g-unit with peaks at 1.2 (dry sod) and 1.6 (wet sod).
Other papers of interest:
  • Cooperrider published 2 papers on soil tripped rollovers, SAE papers Characteristics of Soil-Tripped Rollovers, SAE Paper 980022 and Testing and Analysis of Vehicle Rollover Behavior, SAE 900366 wherein they measured the average coefficient of friction for furrowing in soft soil. Criticisms you may encounter of the Cooperrider research is that the soil field was artificial in that they filled an area with packed dirt. Also, some of the average measurements were made ‘over time’ as opposed to ‘over distance’. (when you evaluate a rollover collision, you need the average drag ‘over distance’ not time). Obviously if a vehicle is travelling sideways and plows or furrows which produces a `trip' then the coefficient of friction during the trip phase must be adequate to stop the translation of the tires and induce rotation of the vehicle about the `trip point'.
An important element in sod or soft soil properties is the moisture content. If you look at Bekker "Introduction to Terrain Vehicle Systems" you will find measurement techniques for characterizing soil/sod.