Min Pile Embed for building over water 1

[TonyES]

I have a client that drove about 50 10" diameter piles along their water front property and now want to build a two story boathouse on it. They were driven 6-8' into the soil with a 4500lb drop hammer. They stick above the soil about 15 feet, than there is a dock and above the dock is a two story structure. The contractor hired a PE that is telling them the piles are fine and we can put this building on them. How can he know that if he doesn't know what type of soil or anything about the installation readings (there were none). I've recommended doing exploratory work to determine our soils. I'm being treated like I'm crazy and an overly conservative engineer. This structure will cost $400,000 and have large doors that must remain operable, excessive deflection will make them inoperable. I'm a structural guy and haven't done piles since college. We have 3kip horizontal loads and 34 kips axial loads on some piles. Am I crazy?

 

[Ron]

Absolutely NOT! You need soils information. Six feet of embedment with 15 feet of exposure with a 3k lateral load is a bit "iffy", considering you don't know the soils info and the point of lateral fixity (if any) of the pile.

At the least, require a load test on the piles.

 

[SlideRuleEra]

I agree with Ron, for 34 kip loads and a $400,000 structure, soil information is essential. A common driven pile requirement is a minimum 10 feet embedment (even when soil properties are known and are satisfactory).

It is possible the that the Contractor's PE has experience on other similar projects in the area... but an educated guess is not worth the risk on this project.

http://www.SlideRuleEra.net

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[PEinc]

Also, has anyone checked if scour will be an issue? If so, the 6' - 8' of embedment could be significantly reduced.

http://www.PeirceEngineering.com

 

[oldestguy]

All of the above sounds very suitable for what is known.

However, I can imagine the difficulty of running a load test. It might be cheaper to bring in another rig and tap a few and calculate from that the probable capacities.

As with many posts on this web site there could be more information provided so the complete picture is presented. For instance how high a drop for the weight and about what penetration per blow so the ENR formula (or other) could be applied. Also what is the history of work along the area? Are there other jobs of similar nature and what has been their history of problems if any? The contractor may have a good bunch of successful experience. Don't knock his methods until you know more about them. While he may not be an engineer, I am many times impressed about the practical know-how of some contractors.
Also for the structure, can the piles be secured by some moment resisting connections? Give enough overall upper end rigidity, embedment may not be of concern.

Finally, describe the PE's statement or report that all is OK. Maybe he went through all this already.

 

[jgailla]

I haven't done geotechnical piling calculations in a while, but isn't 34 kips a bit high for a 10" pile with 6 feet of embedment, to say nothing of the lateral loads.

 

[TonyES]

Thanks everyone. I have expressed these concerns to the client and hope he'll reconsider hiring this guy. I've requested hard data to confirm. He has not submitted any reports yet but I'll make sure to review them.

 

[HouseBoy]

34 kips on one pier out of 50 seems like something can/should be done to spread that load out over more piles.
It def seems like too much load for one pier.

Surprised you say "he doesn't know what type of soil". Seems like somebody would know something if they have driven 50 piles into it. They might not be scientific (no installation readings) but you aught to have some idea of what is commonly found on that body of water.

Lateral load transfer into the soil seems like a real challenge too.

 

[Lomarandil]

As OG asked, are there moment connections at the top (although might be tough with only a 10" pile)? Or any battered piles?

It sounds fishy, yes. Worth looking into for sure, but it might be alright.