Pile not embedded in rock and is under lateral load? 3

[IJR]

I was just curious

You have a long pile that goes all the way down through very weak layers of soil only to touch the first firm layer available, usually rock.

And for some reason no penetration is made into rock.

So you have bearing capacity. Fine.

But even if piles are connected to each other at the top, by a very rigid cap, will you have lateral resistance in the piles.

Nice summer holidays pals
IJR

 

[Ron]

IJR...yes you will have some lateral resistance. Keep in mind that the projected face area of a deep pile is relatively large, thus the unit stress on the soil is reduced as compared to the end bearing condition.

If you looked at each pile as if it were a narrow retaining wall, you would see the relevance of active and passive soil pressures for the soil/structure interaction, thus you can compute the fixity of the pile and its ability to resist lateral loading.

 

[IJR]

Thanx Ron boss, for the fastest and clear response.

What if passive resistance is too small, given say available soil being say, very very weak? shall we then rely on the friction developed by the pile-to-rock contact for lateral resistance, given large bearing force where available?.

Keep in sacred health.

respects
IJR

 

[Ron]

If the soil is too weak to develop adequate lateral resistance, your better approach would be to use batter piles. You cannot consider the friction at the rock interface as providing lateral resistance since no moment is developed in the pile when fixity is not achieved.

 

[emmgjld]

I have dealt with the situation of a very deep (over 300 feet), very soft glacial lake bed deposits. Auger Cast Piling was used. The piling was drilled to 80 to 110 feet, with only a small increase in soil stiffness. ( the only significant resistance was encountered when the auger drilled through the length of a buried tree trunk) No hard surface was encountered, therefore no 'socket' for the pile end was constructed. Virtually NO End Bearing was achieved. The grout pressure during construction probably aided in the side friction development. Load testing revealed significant capacity before plunging failure. A lateral soil resistance was assumed and appears to have been realized. The entire foundation group is 'tied' together with grade beams. After 18 years the piles are still performing well.

Regarding driven piling (closed ended pipe, displacement type) placed in soft soils with 1 to 3 feet of socket for 30 to 60 feet of total pile length. SPT counts of less than 3 blows/12 inches. The actual realized lateral resistance has consistantly been more than assumed WHEN THE PILES ARE TIED AS A GROUP. This also matches the tales I heard regarding bridge construction in Viet Nam, 30 years ago.

I have also seen significant lateral capacity increases when a structural fill in placed beneath the surface slabs on grade.

Carefull review of existing structures, especially older buildings can be very informative.

 

[KAM_imported]

Any soil (no matter how weak) will provide some lateral resistance to lateral loading. Whether the available capacity is sufficient to support the anticipated loads must be evaluated. The programs LPILE (single piles or shafts) and GROUP (pile or shaft groups)by ENSOFT are good and relatively easy to use. These programs account for reinforcement in the foundation element.