Vibrations in concrete structure while concreting

[BECT]

hi ,

I am curious to know if there is any literature available on the acceptance criteria for the vibration in the existing structure if one has to plan to pour new concrete to do some rehab.
We are planning to pour new concrete at one of the Dam site in Ontario and crew is experiencing some vibrations and we are concerned that the we might get cracks during the curing phase and on the top my concrete may take more time to set. I am also more concerned about the bond between new and old concrete because of theses vibrations.

I am thinking of putting seismometer on top of the dam and get some frequency data but don't know what to compare with once I have that. Still doing research but will appreciate your help if somebody in this forum and has experienced something similar and how they handle this problem.

Thanks

 

[r13]

Is there a vault/tunnel in the existing dam? Hard to image a solid/undamaged dam will vibrate under construction load.

 

[WARose]

There isn't (to the best of my knowledge) complete agreement on a acceptable level of vibration during the first day or two of concrete placement. One reference I have (i.e. 'Vibrations of Concrete Structures' SP-60, by: ACI (1979), p.229) gives a acceptable peak particle velocity [PPV] as 0.2 in/sec for the first 12 hours. (I've seen other references stretch that out to the first day.) This reference also gives a acceptable criteria from day 1 to day 7 as 2 in/sec.

0.2 in/sec may seem tight.....but it is not too far off from what you would expect from a lot of construction activity (as long as it didn't get too close to the point of measurement, say about 20-30 feet) with no blasting or pile driving.

Of course, opinions vary. I've seen people say 0.3 or 0.4 in/sec is ok early on.

 

[STrctPono]

I'm curious as to what the source of vibration is?

I've dealt with this issue so many times on bridge widening jobs where traffic needs to be maintained throughout all concrete pouring operations of new to old concrete. I've tried to approach this with a technical theoretical mindset but due to the lack of good literature out there or the lack of funds in our budget to perform any monitoring work... we always end up employing good sound Engineering Judgement.... (i.e. slow traffic down to a minimal speed, pour during off-peak hours, use rapid setting mixes with short initial and final set times, etc.)

 

[r13]

I support the above view, you need to pin down the cause to see if the problem can be eliminated/minimized by "good sound" engineering practices.

 

[BECT]

Hi WARose,

Can I have this paper please?

Hi STrctPono,

The Power house is almost at the toe of the dam and the 5 penstocks are feeding 5 units. The units are 60ft away from where my crew is experiencing the vibrations or the area where I am planning to do concreting . Also there are two mines at a 70Km distance from the dam site. Iam digging into this to find out the actual source.

 

[cvg]

mines located 70k - blasting should not have any significant impact from that very far distance

turbines in good working order have very little vibration

i dont understand why vibration would affect the concrete setting time

 

[r13]

Sounds like a pumped storage powerhouse. vibration could be noticeable but shouldn't be to the extent of detrimental to concrete placing, which for its self requires vibration. I would suggest use a low slump concrete mix to prevent segregation of aggregates, due to the extra source of vibration..

 

[STrctPono]

I'm not sure if this is the paper that WARose is referring to but it seems to corroborate some of what he said.

 

[Retrograde]

ISO4866 has information/guidance on this issue.

 

[WARose]

Hi WARose,

Can I have this paper please?

It's a book....and sorry, I don't have a pdf of it.

 

[Ron]

There have been numerous threads on this over the years. Additionally, many of the studies that are published have to do with pile driving adjacent to piles that have not yet set. Florida Atlantic University did a study about 20 years ago on this....you might check that.