Shallow drilled Pier
Shallow drilled Pier
(OP)
Looking for some direction on how detailed to get on evaluating shallow drilled piers (about 4' deep) subject to Gravity, uplift, shear and moment forces.
All loads are relatively light P=2.75k+- V=1k+- M=6K+- U=5k+_
I'm wondering if the following procedure seems applicable. I would use the concrete weight to resist uplift. Check bearing as P/A possibly add M/S. However I'm not sure if I would need to add M/S if I can argue that M and V can be taken out by passive pressure (similar to pole embedment). If so checks would be:
Wconc>U
P/A less than allowable bearing capacity
V+M/d < less than allowable passive (pole embedment calc)
This may be a problem because I'm not sure how to accurately handle the moment, not sure if M/d is correct or if I should use some equivalent lateral force above the pier.
See attached sketch as well.
Thanks
All loads are relatively light P=2.75k+- V=1k+- M=6K+- U=5k+_
I'm wondering if the following procedure seems applicable. I would use the concrete weight to resist uplift. Check bearing as P/A possibly add M/S. However I'm not sure if I would need to add M/S if I can argue that M and V can be taken out by passive pressure (similar to pole embedment). If so checks would be:
Wconc>U
P/A less than allowable bearing capacity
V+M/d < less than allowable passive (pole embedment calc)
This may be a problem because I'm not sure how to accurately handle the moment, not sure if M/d is correct or if I should use some equivalent lateral force above the pier.
See attached sketch as well.
Thanks
EIT






RE: Shallow drilled Pier
I would not count on it to resist moment and would expect it to move laterally if the horizontal load was significant. I would not rely on skin friction, but the end bearing would carry some gravity load if you clean the bottom of the excavation before pouring concrete.
BA
RE: Shallow drilled Pier
I would handle the moment by applying V at a height to get M at grade.
RE: Shallow drilled Pier
Very small rotations create a "pin" effect, so moment stiffness and effective moment resistance is near zero (unless embedded in rock).
RE: Shallow drilled Pier
ATSE-that is a good point.
So I take it the flagpole embedment equations (IBC 1805.7.? - I think) may not be applicable to this situation. I admit I don't know much behind the equations.
EIT
RE: Shallow drilled Pier
RE: Shallow drilled Pier
The building enclosed, it is a greenhouse.
EIT
RE: Shallow drilled Pier
Based on the allowable soil values, there are equations to increase the allowable as the pier is drilled deeper, plus the uplift will drive the depth, and size too.
If you drill the piers, do not use spread footings for bearing, only the diameter of the pier.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Shallow drilled Pier
The best advice I can offer is to get a soil report from a competent geotechnical engineer, then review the many options for a foundation for this building.
BA
RE: Shallow drilled Pier
Frost line is at 42" below grade. Soils are gravely clay or Clayey gravel (not sure which is correct). However we have not received the official soils report.
I believe they want to use drilled piers because they are thinking it is most economical/cheaper but I will present the option of an isolated square footing to the boss as well.
EIT