Can I consider both friction and bearing for pile design 4

[GeoHint]

many designer only consider either friction or bearing during design. for instance, caison piles usually design for bearing, pipe piles for friction.
can i consider the both for the above piles.

 

[ukengineer58]

Piles utilise friction of shaft and end bearing if ground suitable.

 

[dik]

Check with your geotekkie... due to the difference in stiffness I usually use only end bearing or skin friction...

Dik

 

[hokie66]

It depends on the subsurface conditions. I have used both, and in other cases only one or the other. The geotechnical engineer can normally define the parameters.

 

[Ron]

Both are always present...it is only the ratio between the two that changes.

In some instances you might have 99.9% friction with minimal end bearing...in other instances just the opposite. The usual case is somewhere between...with many variables controlling.

There are even cases where the end bearing must be more than the structural load on the pile (downdrag from consolidating soils pulling the pile down)

 

[molerat2210]

Are the piles bearing on rock or floating? You can use both if the strains are compatible. Piles on rock can develop high end bearing with a small friction component. Floating piles will have high side friction with a little end bearing developing over time and as the pile settles under full load.

 

[GeoHint]

molerat2210
assuming the medium dense silty sands, floating piles.

 

[GeoHint]

my understandind, if the pile is driven piles, the tip friction should be considered. the drilled piles, the friction may be negelectable .

loose to medium sandy soils in all cases.

 

[hokie66]

In loose to medium sand, I would always design for side wall friction only for driven or bored piles, unless they are expanded base piles (Frankipiles).

 

[BigH]

Let's say you are driving a pile into a fairly granular. "Friction" and "End-Bearing" are both "there". You can determine the frictional carrying capacity and then the end-bearing capacity - add the two together and get the total. Now, when the load is applied, depending on how you have determined the safety factor, the load will initially be carried by the friction with very little being carried by any of the end-bearing component. If the load starts to exceed the frictional capacity, then the end-bearing will take up the additional load. Why? Friction takes very little strain to mobilze. End-Bearing takes more strain. - they are not compatible. Friction comes first (with a bit of end-bearing), then as the friction peters out, the end bearing will take on more. I found that the friction might be about 35 to 40% of the ultimate capacity. Using a Safety factor of 2.5 or so, the frictional component would be nearly the same as the applied loading.

For clays - with Nc only being 9, there is very little end bearing and the bulk of the load carrying capacity will be adhesion.

If one is driving to rock, the pile capacity might very well be the material property of the pile.

Anyway that's my late night take . . .

 

[molerat2210]

You can include a fraction of the available end-bearing for the floating pile design. As explained above, it takes more strain to mobilize end-bearing resistance. Some load will get to the tip after several months or years as the pile settles. The end-bearing capacity can be measured with an instrumented pile taken to a plunging failure.