Sheet Piles

[SteelPE]

Fell free to boo me out of this forum if you would like.

I am looking for some very rough guidance in driving sheet piles on granular soils. I seem to remember reading somewhere that it's a good idea to make sure existing foundations are far/deep enough such that the bottom of existing foundations are below a 30-45 degree angle from bottom of sheet pile. This recommendation what to help prevent settlement of the existing foundations during driving. Is this correct?

 

[Ron]

SteelPE....smart of you to be concerned about this!

No, it is not likely that you'll find existing foundations to be that deep; however, when driving or vibrating sheet piles near existing structures you have to take some precautions. Here are a few things to consider:

1. First, do a complete and thorough inspection of the existing structure. You need to mark and plot every crack you can find. Videotape the entire process and take still photographs as well. Particularly important is to mark the ends of existing cracks to see if they increase in length.

2. Make the building owner fully aware of all activities that will take place, whether you are driving or vibrating the piles in place.

3. If you don't already have geotechnical info on the adjacent property, get a few borings done, particularly between the sheet piling and the existing foundations. This is important in granular soils to see where vibrations might be transmitted to the existing structure and to see how dense the soils are presumably below the existing foundations to see if they are likely to densify under the pile installation vibrations.

4. Monitor vibrations during the placement of the sheet piles. Most vibration monitoring devices used now have the capability to set trigger alarms. This will tell you with a loud alarm if you are exceeding vibration limits that might damage the existing structure or cause additional settlement of the foundations.

5. Control the contractor's activities and place on them a lot of responsibility for violating any provisions of the protocol you establish. You'll have to be careful in your specification of these items.

Attached is a nice article that was written by my business partner on the subject. We have both been doing vibration monitoring and testing for many years and he has written an online course in what to look for that is contained in the attached.

 

[SteelPE]

Ron, thanks for the information.

I was recently asked to visit a building that was severely damaged by driving 30' sheet piles 3 feet away from the existing building. The building was load bearing block that developed cracks up to 1-1/2 wide when the foundation sank and may need to be torn down. I was dissapointed to see there was no mention of the existing building in the design documents prepared by the EOR. Seems like an ounce of prevention could have prevented a pound of cure.

 

[Ron]

SteelPE...that probably constitutes negligence on the part of EOR. Consideration of existing structures is something that has to be made in any pile driving project. The potential for damage is just too high.

 

[BigHarvey]

You have several ways to install sheet piles. Main two are :
- vibration with a top vibrator
- driving with a hammer
In granular soils,vibrations will compact the soil which will settle and hence induce settlement of the adjacent buildings. Prefer driving with a hammer which will generate transient vibrations instead of continuous ones, this will not compact the soil but still you will have vibrations. You can find littérature about predicting levels of vibrations caused by pile driving. The disadvantage of driving is noise.

 

[SteelPE]

Ron,

I agree..... but looking at a set of drawing prepared by an EOR while onsite for 10 min doesn't give me enough time to figure out if it was addressed or not. I also don't know enough about the project, just the fact that the building next door was severely damaged. I also know that the EOR placed a footing 15' below grade only a few feet away from the property line (hence the sheet piles). I believe he left it up to the GC to figure out how to construct the footing at this depth (probably citing means and methods). The GC hired a shoring contractor who hired another engineer to design the soil stabilization (which was reviewed by the EOR).

I don't know enough about this, but I have a very similar project on the books coming up with similar issues. The only difference in this instance is that the client owns both buildings. I like to learn from others mistakes hence trying to figure out what went wrong and how to avoid the problems in the future.

 

[SteelPE]

BigHarvey

I believe they installed the piles using a vibrator. Is there any way to use that method and avoid settlement of the adjacent structure say buy installing mini piles to support the building? Or will the mini piles tend to settle as well?

One other problem they were dealing with wile onsite is that they are very near an airport (<1/4 mile). I know the FAA had restrictions on crane heights during construction. So maybe this pushed them in one direction vs another.

 

[Okiryu]

I just remembered saw this link:

http://www.giken.com/en/press-in/principle/practical_use_of_principle

Looks interesting if you want to avoid vibration and noise. Have not used them, though.