Coefficient of friction between granular soil and wood

[Geoduck]

I am looking for a coefficient of friction between a temporary wood-pad foundation and the underlying granular soil.
Anyone know where I can find information on this? I have tried NAVFAC 7.02 7.2-63 but it does not give a value for wood/soil interface.

 

[jdonville]

Geoduck,

I would guess that the wood would be relatively smooth. You may want to think about how that will affect the sliding friction - you could start with the soil-steel f-value and work from there.

good luck

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

The views or opinions expressed by me are my own and do not necessarily reflect the views or opinions of my employer.

 

[Geo69]

Geoduck,

Try looking in the NAVFAC DM 7.02. There is a table on page 7.2-63 that lists friction factors between dissimilar materials including a masonry on wood (26 degrees).

 

[DirtJockey]

In the absense of additional data, I would agree with Geo69, but I would also use the guidance from DM 7.2-194, regarding piles and soil friction.

The friction angle (delta) between timber piles and soil is 3/4 of phi. So, Using 26 degrees as the delta, phi would be 4*26/3, or about 35 degrees. This is reasonable, assuming the soil is properly compacted, and you have the right type of soil. You can refer to Figure 7 of DM 7.1-149, which correlates soil friction angles (phi), with other useful parameters, including relative density by soil type.

Depending on how large your temporary foundation is, the type of soil you have, and your anticipated loads, the friction angle may be an important consideration in your design.

 

[Ron]

Test for it. Easy to do. Place 6-inch square piece of wood on soil. Add 50 lb weight to top of it, and pull horizontally. Measure force required to move it.

 

[Geo69]

Ron has a good point. We have done testing in our lab in the past using a sample of the soil and the dissimilar material. Our testing used clay and geosynthetics for slope stability in a landfill design but any material could be used.