Batter Augercast Piles under Settling Embankment

[gatorgeo]

It is understood that an augercast pile installed at a batter beneath a recently constructed embankment that is causing long-term consolidation of the subsoils will develop moments along the pile shaft. My question is if anyone is aware of any academic or research studies documenting this behavior and quantifying moment development at depth?

 

[ishvaaag]

See p. 1.16-2 in

http://www.state.nj.us/transportation/eng/documents/BDMM/pdf/bmsec16.pdf

that directs to

http://www.fhwa.dot.gov/engineering/geotech/library_arc.cfm?pub_number=42

Apart from that it occurs to me you could consider active push from the tall part and null passive resistance from a degraded downward's slope of the embankment. So, just the total active push of the upper part on all the piles if the piles are together enough, or of 3 times the diameter the width of each on the particular pile if sparsely populated. This was the approach taken by former spanish code for loads on buildings NBE AE-88.

 

[DRC1]

As the embakment settles, any long batter pile will assume a sweep due to the settlement. The mooment in the pile is calculated based on the sweep of the pile. I would have two concerns with augecast piles in this situation : Augercast plies are often not reinforced to the full depth. (Sometimes they are) If they are not, tis could be a problem if the piles are deflected by soil setllement. The other problem is that auger cast piles can have sudden changes in profile which may cause stress concentrations during the bending. Hpiles are often used for batter piles. Pipe pile can also be battered fairly easily. Prestress can be battered, but the weight of the pile makes it a more complicated operation.

 

[Ron]

Draw a free body diagram of the soil movement vs. the pile geometry. As DRC1 noted Augercast piles are not always reinforced to their full depth. If reinforcement does not extend beyond the point of fixity for moment, then the pile can fail in bending.

 

[ishvaaag]

My post was focusing more on vertical piles embedded in embankments than inclined ones spporting the embankments. Quite a miss, this time. Before finding your research items the best one can do is to model the thing in FEM, layers, contact and nonlinearity for the mid to longterm to a non-deformable layer, so typically better a task for someone dealing with soil's FEM frequently.