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How to estimate peak acceleration in rock blasting work

How to estimate peak acceleration in rock blasting work

How to estimate peak acceleration in rock blasting work

(OP)
Anyone can provide some info on how to estimate the peak of acceleration (a) of a rock blasting activity ?  
Most blasting work generally deal with load, delays, velocity and scaled distance; but discuss very little about "a" value. I saw some papers indicated that  observed "a" can be as high as 0.7g.  Does this value depend on distance, type of soil/rock, etc? Is "a" data always collected from the seismograph during blasting ?

Any input of comments ?
Regards

RE: How to estimate peak acceleration in rock blasting work

Unless your suppliers for the explosives can give you a table/graph with rocktype, charge, fudge factor on geological features, distance and stress, you will have to measure it yourself.
I think there might be a paper somewhere that has these values estimated into a table/graph of some sort.

However, it depends where you want to measure the acceleration;  right in the blast volume or some distance away at a critical slope.

My suggestion is that you get yourself a decent stand alone seismic system that can record the data and then you can analyse it.  Something with two or three accelorometers so that any anomalies within the area will stand out.  Meaning, in a fractuired rock mass the energy waves traveling through it goes through a number of processes: convolution, refraction, attenuation, dispersion etc
These 'processes' can be the cause that for some or other reason the measured amplitude at one area might be larger than that of a neighbouring area at the same distance.
Having a mobile system you should be able to get a picture of what the "seismic properties" of your rockmass are and how it changes as the blasting progresses.

Recommended company regarding the seismic system and geophysics involved in such a ask is ISS International.

Website:  http://www.issi.co.za/

Pretty sure they'll be able to give you much more detailed info.

Regards






Anyone can provide some info on how to estimate the peak of acceleration (a) of a rock blasting activity ?  
Most blasting work generally deal with load, delays, velocity and scaled distance; but discuss very little about "a" value. I saw some papers indicated that  observed "a" can be as high as 0.7g.  Does this value depend on distance, type of soil/rock, etc? Is "a" data always collected from the seismograph during blasting ?

RE: How to estimate peak acceleration in rock blasting work

It is important WHY you wish acceleration instead of particle velocity (the usual way to represent vibration for blasting).  Is it for some criterion of damage, or to relate to rock stability?  Be very careful if you try to relate blast vibration to earthquake acceleration criteria, the vibration characteristics are very different, in frequency and duration.  I've seen lots of people get into trouble trying to peel THAT orange with an apple peeler.

A simple (but inaccurate) way is to estimate the particle velocity using one of the textbook equations (e.g., PPV = 160 * SD ^ -1.6), and then convert the velocity to acceleration using a sinusoidal approximation.  Note that we are approximating an estimate!  

If you would like more details, feel free to contact me directly, danderson@schnabel-eng.com

Dr. Doug Anderson

RE: How to estimate peak acceleration in rock blasting work

(OP)
Dr. Anderson
Thanks for the valuable info !
This is the whole point I try to find out. People separate the two subjects apart... is it because they are different ?
1. Liquefaction can happen due to earthquake. There is relationship between the effect of liquefaction and density of existing deposits, particularly fine sand and silt.
2. In blasting, you use this technique to densify silt and fine sand. This means that there is some effects of blasting on particular soil or overburden deposits.
Now what I like to know is How to get the connection between Liquefaction and blasting ? Is there a chart which correlates the effect of blasting and potential liquefaction ?
Are we comparing apple and orange... or apple and crab-apple (or orange and mandarin)? This is what I want to know. How can I ensure that rock blasting work that we plan to do will not liquify all the soil deposits above and nearby of the rock blasting area. How should we limit the blast charge or distance to minimize liquefaction ?
Thanks for the input, anyway
Regards

halim@pangea.ca

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