Micropiles 3

[dik]

I came across a spreadsheet for the design of micropiles based on standard penetrometer values. It's a nicely done little spreadsheet. The skin friction is given as 2x N in kN/m^2 and the end bearing is given as the minimum of (400x N or 10,000) kN/m^2.

Can anyone verify the relationship with standard penetrometer count and the skin friction and the end bearing?

I've deleted this from the Geotechnical forum.

Dik

 

[VoyageofDiscovery]

Hi Dik,

No reference, but my old college notes from my well-known geotech prof shows that in cohesionless soils, 400N as a maximum for depth in cohesionless layer divided by dia. (D/B) <= 10.

Also 2*Nbar for displacement piles, Nbar for H-piles, Nbar is based on field observed and not corrected.

All in kPa. However, apply a min F.S of 4 and 6 to the result for compression and tension respectively.

HTH

VoD

 

[wiktor]

I have developed a little spreadsheet which is based on the correlation in between SPT count and skin friction and end bearing capacity for the piles.
The formulas in the spreadsheet are based on the book by Terzaghi's "Foundation Design" and were dead accurate for 80' long steel pipe piles driven into the sand. For drilled piles I would suggest increasing the SF to 4.

 

[wiktor]

I've missed the link...

 

[Enhineyero]

Hi dik:

Design of piles based on SPT can be referenced under Foundation analysis and design by Bowles

 

[dik]

Thanks, gentlemen... I thought the approach was interesting and wouldn't use it without some Geotechnical input...

I hadn't noticed a response, so read a few papers to determine what correlation there was with N and bearing/shear capacity. The spreadsheet I came across was similar to that posted... different values, but was a similar approach.

Thanks, Dik