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About Robert Cummings, P.E.
Expertise
I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.

Experience
30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Organizations
Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Publications
Mining Engineering, AEG Bulletin.

Education/Credentials
BS and MS Geological Engineering

You are here: Experts > Education > Votech Education > Construction & Contractors > blasting and damaging vibrations

Construction & Contractors - blasting and damaging vibrations

Expert: Robert Cummings, P.E. - 10/28/2009

Question
i have been issued a stop work order because i have exceeded 2" PPV on my monitor which has been placed on the gas main. the gas main is a 2" plastic line inserted in a steel line. we have monitors at the closest buildings and we are under 1" ppv . the gas main is @ 5lf away and @ 6vf away from the top of the rock. the gas main is sniffed prior to our shot and after our shot. we have been blasting for 2 weeks with no problem. now the local gas company has come out and stated we must be under 2 ppv we done some shots that were under 2" but the last day we had shots of 5 and 4 ppv. i am shut down. i read your answer today with some one that has a similar problem.

Answer
A stop work order is pretty serious.

Utilities continue to mis-apply conventional vibration criteria to underground installations, and gas companies get away with it more than other utilities because of the adverse consequences of a rupture. The criteria you mention sound suspiciously like extrapolation of the USBM/OSM criteria which were developed for surface residential structures which are subject to structural amplification factors and single degree-of-freedom response, which is not applicable to buried utilities.

PPV has little to do with the potential for rupture of an underground pipe. What counts is ground displacement, which is directly related to pipeline strains. If the shot is well-relieved, inelastic ground displacement (block movements) at the pipeline location should not be a factor. Close-in shooting without block displacement at the pipeline will not cause a rupture because the elastic strains in the ground, and therefore in the pipeline, are very small. Close-in shooting results in high-frequency movements and it is physically not possible for the ground to move back and forth rapidly and still displace a lot. This is readily shown on a frequency transform which can be developed on tripartite paper.

Your problem is conformance with the specifications. If it is 2 ips, whether it is unreasonable or not, it is the spec, which means you are in the mode of trying to convince the powers that be that you will not damage the pipeline at those levels of vibration so long as the shot is well relieved and you do not have backbreak that shifts the ground in the vicinity of the pipeline -- no amount of monitoring will offer assurance of that. This is why blasters carry insurance (which I hope you do) and blasting skill (which it sounds like you also have).

You can always get out Dowding's or Oriard's books dealing with construction vibrations and pipelines and try to educate the Owner and the gas company. But that is an uphill battle. The other thing you can do is offer to pothole to the pipeline and affix an accelerometer and dynamic strain gages to the pipeline itself and demonstrate what the strains actually are.

Good luck.

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