Blasting near Fresh Concrete 5

[CivilEQuinn]

Hi,

I am a site engineer for a local public utility. We are installing a new 14'x14' reinforced cast-in-place box sewer. Our contractor has previously blasted rock encountered but has recently requested shortening the distance of the blasting operations to freshly placed concrete.

My question is: what are the distance and vibration (peak particle velocity) limits that we should adhere to when the new box slab is placed in relation to the blasting operations. The slab will be 50-100 feet away from the blasting, while the highest PPV we're been getting from monitoring is <1 (.4 -.8 ppv)

I found a study from the early 80's by Ralph Spears (

http://www.concreteconstruction.net...ibrations on Fresh Concrete_tcm45-340996.pdf)

and another (

http://www.concreteconstruction.net...ons Affect Fresh Concrete__tcm45-348668.pdf).

Does anyone know of a more recent study/paper that might be relevant?

Thanks ahead for any assistance.

 

[HSIII]

I would suggest maybe deleting your post here and reposting this in the Structural engineering forum. There you'll have a better chance of structural engineers responding to your quesry.

 

[cvg]

2 ips or less is generally recommended as a safe limit for residential structures and a significantly higher limit is generally safe for concrete structures, however, it depends on the tensile strength. Limits would be highly dependant on the strength of your "freshly placed" concrete.

0.2 ips or less is recommended to avoid disturbing the public


Good resource, not more recent, but that makes no difference - see chapter 7:

Publication Number: EM 1110-2-3800
Title: Engineering and Design - Systematic Drilling and Blasting for Surface Excavations

http://140.194.76.129/publications/eng-manuals/em1110-2-3800/toc.htm

 

[BigH]

Please do not double post - frowned upon heavily - leads to disjointed responses. I've asked that the other post - in Soil Mechanics be removed.

 

[CivilEQuinn]

Oops, At HSIII's suggestion I reposted in the Structural -soil mechanics forum and requested that this post be deleted. I guess the moderation never got to this yet.
Thanks!

 

[Qshake]

I've posted in the soil mechanics forum several links that should be of use.

Regards,


Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Qshake]

just in case that one is deleted:

Here is another source I've found that I'm familiar with:

http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_SMO/FDOT_BDB11rpt.pdf

http://www.dot.state.fl.us/research-center/Completed_Proj/Summary_CN/FDOT_BC352_14_rpta.pdf

I believe that the second link is more applicable.

other links

http://www.allbusiness.com/manufacturing/nonmetallic-mineral-product-manufacturing/1102141-1.html

Another of the Spears article:

http://www.concreteconstruction.net...-blasting-jarring-and-other-transitory-v.aspx

And a TRB report

http://rip.trb.org/browse/dproject.asp?n=11461

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[HSIII]

Yea...looks like your soil mechanics placed one got deleted instead of this one.

BigH...guess that was my bad. Thought this one would be taken care of before anything happened to the soil mechanics one.

 

[BigH]

A proj specs of which I am aware says something like:
1. no blasting to take place within 8 m of concrete less than 3 days old
2. blasting near permanent works within 30 m shall be such that the peak particle velocites
a. do not exceed 300 mm/s for mass concrete greater than 450 mm thick; or new mass concrete that has developed 20MPa strength
b. 50 mm/s existing and new timber frame structures
c. 150 mm/s at transmission line structures.
for 2011

 

[miningman]

Personally I would have no problem blasting 50 -100 feet away from a concrete structure but be aware that your theoretical peak particle velocities only tell half the story. A lot will depend on the abilities of the blaster himself... not the contractor.

The old rule of thumb used to be that anything less than 50mm /sec would not produce new cracks in residential plaster and that something greater than 300 mm /sec is necesary to produce fresh cracks in igneous rock. So all the previously quoted values are in the ball park but if you need to get sophisticated , you need to ask what degree of confinement exists within the blast pattern ?? What type of detonation system is proposed ?? What is the influence of the local geology that will be transmitting the shock wave??

 

[BigH]

There are expansive chemicals that can be used to split the rock without blasting - might be more costly but if you are nervous about potential collateral damage, then it might be worth it.

 

[InDepth]

Why not try a high early strength admixture in the concrete.

 

[DWHA]

What I would do is look in your DOT spec book. There should be a section about max energy that is allowed for jackhammering adjactent to a portion of a structure to remain. And I would specify that that energy at the location of the concrete at a minimum be less that the energy allowed for the jackhammer. Also, not allow the blasting until you have test results back saying that the concrete has reached design strenght. In my experience, most concete meets the design strength in 7 days. This leaves it up to the contractor to take the extra cylinders and if they want to use high-early it is on their dime.