Skin Friction Pile shall be terminated in which layer?
Skin Friction Pile shall be terminated in which layer?
(OP)
Hi,
if someone could help me to understand this problem better.
1. For example if i have 8m stiff clay with underlying 10m loose sand.(only example)
The pile will be mainly on skin friction. So let say i want to terminate the pile 9m b.e.g.l (including 8m into stiff clay and 1m into loose sand). is it possible? skin friction will be higher but what about the settlement of pile under loading? because if it is rock, it wont settle that much, but because it is in loose sand, the settlement could be higher although the calculated/mobilised skin friction is higher(??). So should the skin friction pile only terminated in stiff/hard/medium dense/dense layer not in loose sand layer?
2. let say on top of the those layers in problem no.1 is 5m soft clays. So, does it make any different for me to terminate the pile in the stiff clay or still can be terminated in the loose sand layer.
TQ

if someone could help me to understand this problem better.
1. For example if i have 8m stiff clay with underlying 10m loose sand.(only example)
The pile will be mainly on skin friction. So let say i want to terminate the pile 9m b.e.g.l (including 8m into stiff clay and 1m into loose sand). is it possible? skin friction will be higher but what about the settlement of pile under loading? because if it is rock, it wont settle that much, but because it is in loose sand, the settlement could be higher although the calculated/mobilised skin friction is higher(??). So should the skin friction pile only terminated in stiff/hard/medium dense/dense layer not in loose sand layer?
2. let say on top of the those layers in problem no.1 is 5m soft clays. So, does it make any different for me to terminate the pile in the stiff clay or still can be terminated in the loose sand layer.
TQ





RE: Skin Friction Pile shall be terminated in which layer?
RE: Skin Friction Pile shall be terminated in which layer?
I made up the example. However, i'm sort of calculating a skin friction pile right now. So i need a good insight for my calculation and overall understanding of the skin friction pile. The borehole shows stiff clay overlying the loose sand layer. however, above the stiff clay there's also other layer (sand and clay). Here in my question i wanted to simplify the problem. but still revolving the layer in which we can terminate the skin friction pile.
Can we terminate the skin friction pile in loose sand/soft clay? because i checked the examples in Tomlinson's book, like most piles terminated in at least medium dense sand/stiff or firm clay/.
Help me pls ;)
RE: Skin Friction Pile shall be terminated in which layer?
f-d
¡papá gordo ain’t no madre flaca!
RE: Skin Friction Pile shall be terminated in which layer?
RE: Skin Friction Pile shall be terminated in which layer?
Oldestguy, are you implying that i should only stop in stiff clay (stronger layer), but keep in mind the mobilised skin friction will be lower than the computed value?but u dont take set value for skin friction right. once the pile reach the anticipated depth, u will stop the pile driving right?
But still the main question,Is it still possible for the skin friction tip to be terminated in this weaker material?. so let say 8m stiff sand overlying 5m loose sand and i can terminate the pile at 10m below ground level in loose sand. i still don't get this. sorry
My other colleague say we can but never explain to me. personally i feel it should just stop in stronger layer regardless of the overall skin friction is high or not.
RE: Skin Friction Pile shall be terminated in which layer?
FD, I actually believed the opposite, but yours is probably an example of very clean bottom hole in rock, which would make up a rigid constraint.
In soils, as far as I know (this behaviour is observed in instrumented piles), skin friction is fully mobilized for small settlements, let's say in the order of 1/4", 1/2". Base resistance is fully mobilized for values of settlements usually expressed in function of pile diameter (5%, usually of it).
So if there is a high enough safety factor for lateral shear resistance, base resistance is never fully mobilized. The practice of making sure there is a rigid base layer when lateral resistance is more than enough is actually an emergency plan to avoid plunging of the pile in case something goes wrong.
Bottom line: if the succession is mostly clays with a decent Su (which will be reduced somewhat in the calculations), then the base resistance should not be really vital (of course you loose the back-up plan against plunging). Load tests should suggest this aspect is the one which governs, with very little settlement.
In sands it's maybe harder to achieve a good lateral resistance, unless piles are driven where sand is densified and K is higher. Friction angles are usually not the peak ones.
RE: Skin Friction Pile shall be terminated in which layer?
RE: Skin Friction Pile shall be terminated in which layer?
If we want to try a design optimization though, if that's necessary, some experimentation may be carried out by testing piles before the real job is started. If the settlements keep very low, then there is no load transfer to the base hence there can be (theoretically) no settlement at the base.
One issue you may rise is long-term base settlements and that might be a concern if lateral friction is lost to an extent after time.
Again, a stiff base layer makes you sleep well at night but, if sufficient proof of stability is given in the absence of a base stiff layer (calculations supported by load tests) would you be all right? I'm speaking of non-displacement piles here, just drilled piers.
RE: Skin Friction Pile shall be terminated in which layer?
RE: Skin Friction Pile shall be terminated in which layer?
That's one situation where the Emergency exit of a base bearing layer is definitively valuable! In displacement piles the conditions are obviously different since the soil is densified by the driving energy if granular, also remoulded if cohesive, but I would have to reason about the overall effect since I've only dealt with non-displacement piles, usually large diameter.