Shock waves from implosion demolition

[Patgeotech]

My client plans on imploding a nine-storey building on the site we did geotechnical investigations for.

My concern is whether the shock waves generated by the implosion will or will not affect surrounding buildings (historic buildings). The underlying soils comprise of sand up to 8.0 metre thick underlain by competent rock (shale).

My thoughts are that since the water table is high (within 1.0 metre of existing ground surface) and that the imploded rubble will provide a 'cushion' for the shock wave, that the shock waves will not be a problem.

I would appreciate to know what experience has been had by others regarding implosion demolition and ground induced shock waves. I would appreciate your comments.

 

[civilperson]

Buy a big insurance policy and have at it. The premiums will tell you the likelyhood of occurence.

 

[msucog]

keep in mind that water is practically "incompressible". i've never dealt with implosion shock waves, but i do a far bit of seismic refraction which utilizes a compression wave (hammer striking the ground). i picture the building implosion being a big compression wave as it hits the ground-there again, i've never dealt with particular scenario. ground water typically shows up with a much faster velocity than your typical soil. it will usually show up at around 3000 f/s or about the same as partially weathered rock. don't blasters have problems with making shots on overcast/cloudy days because the sound waves are confined in a sense?
a few years back, i had to get a little blasting done next to (1000-1500'+ away on the other side of another small building) a well known disease research facility. after our initial blast to remove rock, we were informed that we had cracked a 5th floor 8-10" thick slab in a highly contagious research lab. they didn't how bad the cracks were because it would take a week to disinfect the lab for someone to go in and evaluate the floor. as you can imagine, it didn't pan out quite like the people had claimed. as i'm sure you are well aware, i suggest that you cover every angle possible when dealing with blasting and people looking to make a claim of "damage". good luck.

 

[dik]

It's out of my league, but without the water, I would suspect that the sand would have a fair amount of internal friction and damping and there would be little problem... is it possible to draw down the water table with well points? with the water, however, if the sand is saturated it could transmit the compression wave quite effectively. There is also a possibility that the water in the voids could attenuate the wave quickly... depends on the degree of saturation. If you drill down below the water table, does the hole immediately fill up? The faster it fills up, the greater likelihood that shock wave will be transmitted.

You might want to take a whole pile of pre-demolition photographs for comparison of damage.

Dik

 

[TDAA]

Did your report cover the demo work, or specifically exclude it? If you did not include it, I would leave all aspects of it up to the demo contractor, and their insurance policy. As mentioned, I would be sure your client does a fair amount of documentation, before and after the demo. Pictures and video, with good notes.