Blasting Near Underground Utilities

[deeman]

Is anyone aware of any regulations or rules of thumb on how close to existing underground pipelines blasting should be allowed. We have an existing 12" sewer force main which is about 8 feet from where a contractor is preparing to blast for a new 18" trunk sewer. The gravity sewer will be about 10 feet deep while the adjacent force main is 3 feet deep.

 

[sam74]

the utility company who maintains that line will have regulations regarding blasting limits from their lines from my experience. I was unaware of this until they shut the job down that day and the contractor was forced to rent a hoe ram. The contractor had previously been blasting within the limits with low charges before the utility company caught them drilling.

 

[deeman]

Actually, we are the utility. We have always used a rule of thumb of 20 feet minimum, but this case is a little different. There is plenty of solid limestone here and the contractor has been beating and pecking the heck out of it for over a month. It has gotten so bad that he was only laying one stick of pipe a day. It was taking the rock trencher almost 8 hours to get to 5 feet. He has hired a special blast contractor to come in and test to see if the method will work. The company is Nonex Systems and they claim they can blast right up to the edge of the force main trench and not disturb it. Even claiming that a seismograph would not pick up the detonation. I am witnessing the test today so I will try to post what I see later.

 

[sam74]

My experience was with an 8 inch waterline being laid beside a 2 inch gas line. The gas utility limited the contractor to 10 feet. They had been using small charges with no problem within 5 feet of the gas line. Had the contractor not busted a miss marked service line the gas company would probably have never known. I would be interested to here about the results of the test. I imagine you will be needing a much larger charge to blast a trench for an 18 inch line 10 feet deep.

 

[cvg]

request a blasting plan and individual shot plans
monitor settlement, peak particle velocity, energy ratio and airblast pressures. Put limits on these such that only small charges can be used.

 

[deeman]

Well I witnessed the test and, true to form for this limestone, it was not successful. The charges were set at 5 feet deep and there was breakage from 3 to 5 feet but nothing above 3 feet. Their plan is to bring in bigger drilling equipment and try the larger Nonoex charges. I'll try to post again after the next test.

 

[exploengineer]

Normally, as long as the pipe is put of the fracture zone, there is usually not a problem. We've blasted as close as 2 feet without damage.

Use a series of test blasts if possible to determine the area of overbreak. If this is not possible, use the smallest charge diameter possiblw with really tight blast patterns.

Frank Lucca M.I.Exp.E.

http://www.terradinamica.com

 

[chicopee]

dont even attempt blasting near the 12" sewer force; however there are chemicals which will expand upon activation and crack rocks but predrilling is a requirement.
Unfortunately I dont remember the name of such chemical and that should not be hard to find out.