AboutRobert 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 20+ years as a geotechnical engineer and minerals engineer for mining. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for heavy construction.
Organizations Society of Mining Engineers, Association of Engineering Geologists, and International Society of Explosives Engineers.
Question Could you suggest some references comparing various rock excavation techniques (blasting, mechanical removal, chemical splitting, trenching, etc.) for civil projects (as opposed to mining applications). I'm preparing a geotechnical evaluation of proposed water main trench to be constructed in close proximity to other buried utilities, including a gas main, under a 3-lane highway in very hard granite and diorite. I'm particularly interested in comparing typical cost and production as well as advantages and disadvantages of the methods. Thanks!
Answer A great question. Until you brought it up, it had never occurred to me that I know of no single reference that compares non-blasting methods of rock excavation in the way that you want. Maybe I should write one...
The reason is that non-blasting methods tend to be so expensive that nobody does much comprehensive analysis. And the methods tend to be proprietary, as are the cost data.
You are going to have to put the information together on a site-specific basis. Vermeer might be able to provide you information relevant to production rates and costs for rock trenching. Caterpillar should be able to provide information on hoe-ram production rates, and probably unit labor and equipment consumption (but probably not costs). Daigh Chemical can probably give you information on expansive grouts. For other options, like hydraulic splitters and simply pre-drilling to weaken the rock mass and then free-digging it conventionally, you are just as well using RS Means for cost estimates.
Of course you, being a professional, know that the manufacturers are going to paint the rosiest picture they can ethically get away with. So treat what they say with some judgment.
I do these kinds of assessments for a living and know that this can be a challenge. Obviously this is not the right forum for sucn an analysis. I will can tell you that the major disadvantage of a lot of these methods is that you still have to drill holes, only lots more of them than you would for ordinary production blasting. My view is if you are going to drill a lot of holes, you seriously look at putting some kind of charge in them, even if it is a propellant and not a high explosive. By high explosive I mean use detonating cord, fill the holes with water and just divide the rock into pieces without much displacement. This in my view is better than pre-drilling and then spending hour after hour splitting rock hydraulically, waiting on expansive grout that generally does not displace the rock at all, or hacking away at it with a hoe-ram at $300/hr. Relative to each other, non-blasting methods have some advantages, but they tend to pale when compared with the uncertainties and high unit costs.
