Rock blasting vs. rock excavation
Rock blasting vs. rock excavation
(OP)
I have a road project that is designed in an old creek bed, with large partially exposed rock (18" to 8' in diameter). Based on the geotechnical report, some of this rock is fractured and is "rippable" by a large excavator, other rock is expected to have to be blasted. Since the majority of the rock is not exposed, a lot of the actual size and type of rock to be excavated will have to be determined in the field. In order to try to accommodate this, we will be going with a unit cost bid schedule for the contractors, so that as actual quantities vary from the bid quantities, we can hold the contractor to a set fee per unit.
We have kept most of the road in fill, so I do not anticipate much more than 10% of the overall earthwork volumes to include rock removal/excavation. So, my question is, in a bid schedule is it typical to separate "Rock Blasting" from "Rock Excavation," and if so, do you differentiate the two by size of rock, or some other means?
TIA
We have kept most of the road in fill, so I do not anticipate much more than 10% of the overall earthwork volumes to include rock removal/excavation. So, my question is, in a bid schedule is it typical to separate "Rock Blasting" from "Rock Excavation," and if so, do you differentiate the two by size of rock, or some other means?
TIA





RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
Attending Underground Singapore 2007 conference back a year ago, there was an afternoon devoted to geotechnical baseline reporting. This might be the way to go. The geotechnical engineer will give the "%" of rock that he estimates will require blasting and the "%" of rock that can be ripped - rock being classified as particles greater than 1 m3 or some other volume. The contractor is given this information along with probably locations of each. This forms the baseline of his bid. If the blasting of rock is more, then he would be entitled to more money. If less, it would be a wash. This results in shared risk. Again, though, one is back what is rippable if it can't be 'proven' by a trial. In this case have an engineering geologist or geotech experienced in rock that would be agreed as independent by both contractor and owner/engineer. Then site decisions could be made by the independent expert when the two contracted parties cannot agree - sort of "on site" arbitration.
Just some thoughts.
RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
Similarily, a contractor who has a D10 / D11 sitting idle may be willing to take on the "ripping" risk more confidently than another contractor who feels he might have to sub contract the rock work.
I agree that the more geotechnical information that is provided to the bidders should reduce the contractor's risk...... and therefore his temptation to pad his bid..... but by giving the contractors the choice as to their proposed excavation techniques, you are allowing them to present their owm areas of expertise to both your and their financial benefit.
On a personal note, Im a great believer that explosives are a VERY cheap form of energy, and if in doubt, I will always drill and blast rather than risk excess wear on my heavy equipment.
RE: Rock blasting vs. rock excavation
Hearing that "rock is probably my biggest headache," is actually reassuring, because this was my concern, and I guess I was not overthinking things.
Based on all your advice, I'm going with one line item - "rock excavation and stockpile." Trying to potentially define the means and methods to the contractor also is something I want to avoid.
Since I know my original quantity will vary from actual quantities, I will recommend to the owner that he hire the geotechnical engineer to be on-site during construction to verify the overall quantities of rock excavation vs. standard excavation, and also to define the difference between the two prior to the bidding process.
RE: Rock blasting vs. rock excavation
The biggest advantage to going unclassified is noone has to measure anything, which as mentioned above can be a real pain. However, if you don't have enough information to make the contractors comfortable, or if conditions vary wildly, any contractor worth his salt will want a substantial risk premium.
If you want to include an allowance quantity, make sure it's something the contractors can come reasonably close to verifying or you're begging for unbalanced bids. Finally, is there any reason you can't set the unit prices in your bid documents? Of course you need to make them something reasonable for the conditions and market.
RE: Rock blasting vs. rock excavation
from a contractors point of view...
i would get a geotech to go out and grab some x-ray diffractions on the rock to determine the exact qty of non-rippable. At least this way you will be able to determine yourself how much rock is present and the exact locations - thus you might be able to include a provisional item in the schedule for this (and bulk the $$ up) or leave it out, and keeping in mind that you know how much rock there is, then you might be able to reduce your tender and make up for it (and more) with this variation.
knowing where the rock is, and determining when you will come across it in your works programme will also be important.
from your point of view... id also just get a geotech in to let you know exact qtys and where, and then let all the tenderers know.. you will expose yourself to less risk this way.
RE: Rock blasting vs. rock excavation
This is a very remote site, with very thin roads as access, so mobilizing anything bigger than a D9 will be a major challenge. The entire road construction includes about 15k cu. yds of cut and fill, so paying for x-ray diffraction to determine sizes of rock is probably finanicially infeasible for such a small job. I'm thinking that blasting will be the most likely way the contractors decide to remove the rock.
I still think getting the geotech involved prior to going to bid and during the construction process will be my best route.
RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
You migh want to take miningmans advice and leave it up to the contractor to blast or rip...under most conditions I would definitely blast
RE: Rock blasting vs. rock excavation
Where geographically is this project located?? IMO, some of the posts here may be factual but might also be confusing for someone unfamiliar with the practicalities of blasting.
Yes subdrill and overbreak are facts of life, as is oversize, and issues related to mobilization etc etc.
If I understand previous posts correctly, this is a very small job in a remote area. 15,000 cu yards total, only 10% of which is rock. I would be a lot more concerned with the logistics of mobilizing the equipment, and living arrangements for the crews.
Remote is subjective. Helicopter support?? Dedicated camp??
RE: Rock blasting vs. rock excavation
With regards to the site "remoteness." Using the term "remote" was a little misleading; I should have stated that the access to the site is "limited." Access to site is via a 7-8 mile gravel road, no more than 20' wide, with sharp curves in areas. Even bringing a low-boy to the site will be a challenge.
RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
RE: Rock blasting vs. rock excavation
I think you might be setting yourself up for an unbalanced bid offering two pay items for rock exc. I'd leave it their means and methodology. I suspect that this would in keeping with your DOT's standard practice, it is here.