Vibration Assessment of a Structure 1

[HSIII]

Hey all,

A client of mine is going to have sheet piles placed close to (200' to 300' away from) his commercial structure. He wants a vibration assessment done on the structure. I have a fairly recent (3 years old) geotechnical report of the site soil conditions. In your opinion, should anything else go into consideration besides age of structure, type of structure, and overall general condition. Also, how would those weigh into "factoring" the typical peak particle velocity in this area (typical peak particle velocities in this area are usually assumed to be 0.04 in/sec for blasting/short impact and 0.2 in/sec for vibratory/hydraulic hammer type operations)?

Thanks in advance.

 

[msquared48]

Did the Geotech address the susceptibility of the underlying soils to any liquefaction in the report?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[HSIII]

It's maily bedrock approximately 2' below bottom of footing elevation. No real chance of liquefaction, but I think because of the existence of bedrock that I should knock down the PPV's a touch ("factor", if you will)

 

[Ron]

It doesn't matter what the "standards" for the area are. Set up a monitoring scheme and pre-construction survey/post-construction survey of you client's bldg.

Set triggers for the monitoring conservatively so that the structure does not feel critical vibrations. If the triggers are reached, stop the activities immediately.

Monitoring during the installation of sheet piling or other vibration inducement is necessary and should not be ignored. If your client elects to forego monitoring, either you back out of the job or you get a clear disclaimer of responsibility and a clear indemnification of damage.

 

[HSIII]

Ron,

So would you say a continuous run over, say, a week during operations with the trigger set at 0.1 in/sec would be sufficient, or overkill?

 

[Ron]

Depends on the soil conditions and type of construction you are trying to protect. Might want to trigger at 0.05, particularly if older structure.

Make sure that when you monitor, you are at the closest point to the structure with the operations. Monitor both the ground and the structure.

If there are any existing cracks in the structure, be sure to set crack monitoring devices as well.

Do a very details pre-construction survey of the structure and record with video and still photos. Highlight existing cracks with a lumber pencil before photographing and clearly find the end of the crack and mark it so that progression can be measured.

Good luck.

 

[vaquers]

The soil properties will influence the wave propagation. On the other hand the peak particle velocity helps you to evaluate possible non-building damage. I'm agree with Ron, but before setting up a survey I would estimate the peak particle velocity with the elastic media theory (see Lamb and/or Pekeris). In my opinion before setting up a survey you should know what values you are expecting to measure. Regards,

Sebastian