What is the skin friction values of sand?

Question

What is the skin friction values of sand?

atef81 (Structural)

(OP)

12 Jul 23 03:53

Hi,
I need to design pad footings in sand. The current design philosophy used in my workplace is to utilize skin friction as one of the methods to combat uplift in footings.
The particular project I am working on has footings founded in sand, with a separate concrete slab pavement poured on top.

I am trying to find values for skin friction of sand.

Any suggestions?
Thanks in advance.

1503-44 (Petroleum) · Answer 1 · 2023-07-12 12:16:11

Sounds somewhat dangerous to depend on sand friction on a footing for uplift safety.
Uplift failures are often high consequence.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

LittleInch (Petroleum) · Answer 2 · 2023-07-12 14:26:37

"Sand" is far too vague though to be useful.

Moisture content in particular, grain size, friction against what - smooth or rough concrete?
Any silt or other material like that will make a big impact.

amount of compaction / surface loading / water table / rain fall etc will make a big difference to this.

What do they / you use for concrete piles?

A favourite phrase of mine is that friction is like an unreliable friend - never there when you need it, but can appear at precisely the wrong time when you don't.

Best you will get is a range - my guess is 0.1 to 0.4....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

GeoEnvGuy (Geotechnical) · Answer 3 · 2023-07-12 14:45:07

I had a structural engineer once ask what is the friction between bedrock and concrete. I responded with which concrete will be used and how will it be finished, precast, or poured in place, if poured what prep will they do as I only have a 2-inch core surface to run a test on for interface friction angles. The point is you want to know the friction between 2 materials, it's not practical to test this beforehand therefore it is a literature review that your firm should be able to justify what they use and why.

LittleInch (Petroleum) · Answer 4 · 2023-07-12 16:37:18

Wasn't one of the more pathetic (IMHO) excuses the bridge designers for the FIU concrete bridge which collapsed a few years ago that they had used a certain friction value for the "roughened" cold joint between the deck and the spar which moved, but this was reduced because the constructors hadn't roughed the joint?? Now I think that was the least of their FU's but they were clinging to it like glue. Hope you never have to do the same for uplift friction.

A case where my unreliable friend had not turned up...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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What is the skin friction values of sand?