Design of Deep Foundations, Caissons and Piles

[alandjen]

I am a structural engineer in the Philadelphia region. Within the past year or two, there has been a trend where the design of the CIP piles, caissons, and concrete-filled pipe piles has not been provided by the geotechnical engineer for the project. My questions are: 1) Have other people seen this trend, whether in Phila region or other?, 2) Who has the responsibility of the design of these elements - structural engineer or geotechnical engineer, or some combination of both?, 3) How can a structural engineer design a deep foundation element, other than the code-required minimum seismic steel acting as dowels, etc, without the knowledge and tools required that a geotechnical engineer has, and knows how to use/analyze results?

Thanks

 

[JAE]

alandjen,

My experience in Texas (where drilled/belled piers made their first appearance) was based on this concept:

1. Geotechnical Engineer develops the geotech report outlining all findings and recommends drilled piers.
2. Geotechnical Engineer provides in the report various design parameters - max. allowed end bearing pressure, skin friction (for non-belled piers) and requirements for uplift forces that may develop from expansive clays.
3. Structural Engineer designs the structure, determines the loads on each pier, and then determines shaft size, bell size, approximate depth, and required pier reinforcing based on the Geotech report.
4. Structural plans indicate that bids be based on an assumed pier length and the contract documents include a unit cost for additional, or reduced, length of piers in the ground.
5. Structural drawings indicate all pier information except that the pier depth is dependent upon verification in the field. This might be that the structural engineer requires that the contractor notify and allow the geotech on site to verify if the proper strata is reached and if there is any reason to lengthen the piling.

 

[msucog]

we (geotech) provide soil parameters and approximate size of pile since they are inter-related to supporting the structures. we'll provide an estiamte of required depths for support based on boring data and analysis. the structural will design the caisson itself (reinforcement, concrete, etc). the geotech must be involved during the field work due to the liability associated with their recommendations as well as the ibc special inspection requirements.

the structural engineer and geotech do their seperate parts to form the whole. now if the particular subject was a geotechnical structure such as an mse/srw wall, then since the mse designer is designing a geotechnical structure, they are responsible for determining the design parameters and everything related to the walls (again since they are designing geotechnical structures). the geotechnical engineer provides input related to the test results of the onsite soils and passes along information about the boring information, geology, etc (in other words, observed conditions). likewise, the mse designer must be involved with the construction of the walls since they are responsible for the design and confirmation that everything was constructed properly. as mentioned for the caisson scenario, the geotech does their part and the structural engineer does their part. it's two different scenarios but i thought the analogy might help.

 

[fattdad]

This is not an unfavorable reaction to MSUCOG, I'm just quoting him (her?):

the structural engineer and geotech do their seperate parts to form the whole.

I think here's where the body is buried. The OP is referencing a problem where the structural engineer and the geotechnical truely are doing their separate parts, but not resulting in the "whole". This is what I hate about our profession, there is often not enough communication between the structural engineer and the geotechnical engineer when the scope of work is developed (i.e., before the field program and the report is issued). Many HUGE problems could be avoided if this weren't true.

Off my stump. . . .

f-d

¡papá gordo ain’t no madre flaca!

 

[msucog]

very true. i figured out a long time ago that lack of communication makes any situation harder than it has to be. with caisson work, i haven't run across too many problems with SE(but we happen to talk with the SE's we deal with).

 

[Riggly]

I normally get the loads from the structural engineers, and perform the analyses-axial capacity, lateral capacity, settlement etc. The structural engineer will use the results of the analyses - bending moments, area, etc to reinforce the caisson/drill shaft. There has to be close collaboration between the structural engineer and the geotech. I believe the soil part of the design is more critical in the stability of the pile, and therefore the geotech should even have a greater role in the design of the pile.