Construction & Contractors/Northern Calif Drill and Blast Costs
Robert....I am a GC on a 50 acre site just east of Sacramento and was wondering what ball park drill and blast costs would be for hard rock with drill depths to 15'. Can you estimate a per CY range? Over 50k CY of rock.
I'm sure you know all the variables that go into drill and blast costs -- access, mobilization distance, whether there are surrounding sensitive areas, need for pre-blast surveys and monitoring, fragmentation requirements, controlled blasting requirements. Without this kind of information it is impossible to provide a definitive answer. It's like someone asking, "how much does a house cost?" without providing any more information than the square footage.
Here are some of the questions that go into this. Is there controlled blasting required? Is there a decent set of cross sections from which to do the blast design? Where are the underground and overhead utilities, if any? Is there special monitoring required? How hard is the rock? How densely fractured? What is the access like? What is the end use of the blasted material -- riprap or embankment fill or just waste? How tightly must fly rock be controlled -- will mats be required? is the GC going to move the material so as to establish a good surface to drill from? Who is going to pioneer the cuts? Are the neighbors cooperative or will there be difficulties? Are pre-blast surveys required?
Not knowing these makes providing a reliable estimate impossible. Controlled blasting in an urbanized area where the adjoining land users are protesting the project is far more expensive than blasting out in the middle of nowhere.
Nonetheless, you asked for a range, so here is the basis for a starting point.
If the drill depth is 15 ft on average I'd assume the pattern would be around 6x7 and the subdrill would be 2 ft, so for an average shot volume of 3,000 cy you'd need around 150 holes for production only (more if controlled blasting is required). Using average daily drill production rates of about 1,000 lf and what I think would be approximate drill costs in that area, and assuming that a crew of 4 would be required to load the shot with an average powder factor of 1.0 lb/cy I get around $5.00/cy. In this I am neglecting mobilization and certain management and startup costs because they would be spread out over the entire 50,000 cy. If fragmentation is not an issue and the rock is not real hard, the pattern could be widened and the cost could drop to maybe $4.00 or even $3.50 if the subcontractor is real hungry. However, I think it is more likely that there would be add-ons or site issues that could double or triple the cost.
Pure and simple, there is no way to be more helpful without more information. A biddable blast cost estimate must have a site visit.