Timber piles hitting bedrock at 5ft below grade 1

[Ben29]

I am designing a boardwalk and commercial building in coastal flood zone AE. We are using timber piles for the majority of the site. I have one area where I am concerned that the piles will hit bedrock at 5ft below grade (see image below). What do you suggest we do if this happens?

 

[1503-44]

Stop driving.

You should think about alternate foundation types now.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[HTURKAK]

If this happens ? In this case you are not sure if this will happen..

Stripping the 5 ft soil and construction of spread footings or a mat supported on bedrock could be an option..

 

[dik]

Or even end bearing 'caissons/piles' or whatever you would call them... 16" or 24" dia sonotubes...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[1503-44]

I thought the sonotubes would be too weak in lateral stability, something that this application suggests to me could be necessary. But heck, the potential to lose sufficient lateral soil support from erosion scares me just as much as relying on it in the first place. Personally, I'd be thinking sheet pile box and backfill, or tall concrete piers on footings, or a mat foundation.

A black swan to a turkey is a white swan to the butcher ... and to Boeing.

 

[dik]

...make them bigger, reinforce them and provide lateral ties... it's easy to do. If auguring, then make them 30" so you can go down inside them to clean out the bottom... If the rock is sound, you don't need footings.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[Ben29]

Construction has not started yet. We haven't submitted permit drawings yet. But based on the geotech report, I suspect that this condition might occur. Elevation of bedrock changes drastically throughout the site.

 

[dik]

as long as you are not on a rock 'hillside'... bearing should be flat... you can have different length piers/piles/caissons...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[BridgeSmith]

If you need lateral resistance from the piles, you could have them auger a hole in the bedrock the same size as the pile to get the required lateral stability. We do it for steel H-piles for bridge foundations sometimes. If may not be economical compared to using a different foundation type, though.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[SlideRuleEra]

Ben29 - You have to meet FEMA requirements for coastal construction in AE zone.

Follow FEMA recommendations or risk having a design that will not be insurable:

Link to: Home Builder's Guide to Coastal Construction, FEMA P-499

Reinforced Masonry Pier Construction, Technical Fact Sheet No. 3.4 is attached.

 

[Ben29]

Sliderule - thank you much!