How close is too close when driving piles

[jrl802]

Hello all.

I am working as the geotech engineer on a project where we will need to drive some sheet piles and some timber piles in a heavily urbanized area. We will be very close to existing piles for bridges, etc..

Is there any information out there be it papers, guidance, etc... That could help me and the structural engineers determine if the distances we are keeping from the existing foundations are ok?

In essence we want to now if there is a way to calculate how far we need to be in order to minimize any negative effects on teh exisitng foundations.

Any direction will be appreciated? Thanks!

 

[JedClampett]

My experience is limited, but the distances can be closer than you think. We drove piles within about 50 ft. of an existing structure and the Geotechnical Engineer assured us that damage would be minimal. And he was right.
Saying that, perception of damage is a lot more important than technical concerns. You need to go into every nearby house, doghouse and cathouse, survey the structures and identify existing cracks in plaster, drywall and mortar joints. Because if you don't, there's going to be a lot more damage paid for than can be attributed to any construction operations.

 

[InDepth]

I think you can use your basic pile stress distributions based on assumed friction
1) During driving
and 2) Permanently under load

You can imagine the driving process as a "downdrag." So what you need to answer is what is the width of the sheet pile and pile influence zone. usually a cutoff of 10% additional stress is appropriate to determine how close you can be. If you want to make it really close, you could potentially try decreasing the sheet pile friction by sand blasting. You could also use CSF piling or micropiling as alternatives. Geometric layout relative to the adjacent piles should also be reviewed.

You probably should perform a cross section and understand if you are going below the existing bridge piles. If you are you may need to add tie backs to increase the soil confining pressure to maintain the bridge pile skin friction. Alternativeley you can limit the amount of traffic on the bridge so that you can calculate a temporary case where the required pile length is below the bottom of excavation (capacity is greater than demand, thus not requriing full pile length.

Plenty of other issues, but this should get you started.

 

[Ron]

Pile-to-pile distances are usually set at 3x pile diameter.
As for pile to existing foundation, just monitor the existing foundation for movement and vibration and you should be fine. I've been involved with projects where piles were driven within 5 feet of existing foundations without issue.

 

[PEinc]

In my experience, you can't tell how close to a building you can drive piles without "damaging" the adjacent structure. Even if you do not damage the building, you may be sued for some claimed damages whether real or bogus. My advice is to talk to the adjacent property owners before you start work and let them know what you want to do and what they should expect. Then, do what Jed said. Also do vibration monitoring as you approach the building. If the vibrations get too bad, if you notice damage, or if the owner claims damage, you better stop driving, check out the situation, and have a Plan B for installing the piles (such as pre-drilling before driving drilling or setting the piles into drilled holes. What your Plan A and Plan B should be really depends on what type of piles you are installing (soldier beams, bearing piles, sheet piling).

http://www.PeirceEngineering.com

 

[BigHarvey]

A very good paper about estimation of peak particle velocity expected in terms of hammer energy and distance was published in Ground Engineering in nthe may 1992 issue ( "Ground borne vibration from piling" by PJ Whyley and Prof RW Sarsby ). If you know the PPV admitted ( will vary accordingly with local code, building condition, etc ).

 

[Ron]

I didn't finish my answer before....I've also been involved in projects where damage was done from driving piles too close to a structure. As others have noted as well, monitor the vibrations.

I would also suggest a detailed pre- and post- pile driving condition assessment and crack survey of the existing structures nearby.

As BigHarvey noted, determining and limiting the peak particle velocities will help tremendously. Vibration monitors can be set to "trigger" an alarm when certain vibration levels are reached. There are numerous sources of PPV limiting values, whether the structures are new, old or historic.

Charles Dowding's book on construction vibrations is good. Another good source, but harder to find is Richart, Hall and Woods' book on vibrations. Also check CALTRANS....they have a good vibration manual.