Cost of trench Rock Excavation
Cost of trench Rock Excavation
(OP)
I'm in search of rock excavation (Bedrock)cost for trench.
My project is a 24-inch gravity sewer approximately 2600-feet long. Any elaborations will be very appreciated. I have to excavate soil prior to the rock.
Thanks
My project is a 24-inch gravity sewer approximately 2600-feet long. Any elaborations will be very appreciated. I have to excavate soil prior to the rock.
Thanks





RE: Cost of trench Rock Excavation
type of rock, hardness
depth / width of rock cut
weathering, fracturing, jointing of the rock
is blasting allowed?
are you in close proximity to other utilities? structures?
RE: Cost of trench Rock Excavation
Access (could you use a ripper or milling machine on a backhoe)?
Groundwater?
Underwater trench?
Noise and dust limits?
RE: Cost of trench Rock Excavation
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve
RE: Cost of trench Rock Excavation
Original Thread:
I'm in search of rock excavation (Bedrock)cost for trench.
My project is a 24-inch gravity sewer approximately 2600-feet long. Any elaborations will be very appreciated. I have to excavate soil prior to the rock.
CVG's response:
you need to provide more information including:
type of rock, hardness
depth / width of rock cut
weathering, fracturing, jointing of the rock
is blasting allowed?
are you in close proximity to other utilities? structures?
My answer to CVG:
Rock description: a mixture of highly weathered shale and hard limestone (compressive strength of limestone goes up to 750 ksf)
Depth: Ranges from 4 feet to 20 feet beneath soil
Trench Width: 48"
Blasting is limited. In areas of suspected trenching into the hard stuff, blasting is allowed. Yes I am in close proximity to another structures, which is being replace by the new and bypass operation will be in place.
RE: Cost of trench Rock Excavation
A hoe ram can be used to break up the rock, again the production rate depends on the amount and hardness of the limestone.
$70/cy sounds reasonable
RE: Cost of trench Rock Excavation
If your excavator has the requires reach, cutting that rock of that strength would be no problem.
What is your excavator make and model? That info would be required for a production estimate.
RE: Cost of trench Rock Excavation
8' cut = $22/linear foot.
20' cut = $40/linear foot.
Frank Lucca M.I.Exp.E.
www.terradinamica.com
RE: Cost of trench Rock Excavation
I have worked as an estimator and project manager for a pipeline construction company for a lot of years, and we ran into a similar situation on a project in the middle of a city street about 15 years ago. There were commercial buildings on each side of that street, which did not help. The hard rock is only the beginning of your problem -- the shale is possibly the most treacherous thing to excavate, as it may be difficult to cut, but then, once you get about 10-15 feet down, the shale may fracture and huge blocks break off and fall into the ditch, without any warning. This is especially dangerous because you have to excavate that hard rock down below--and that cannot be readily done without creating a whole bunch of vibration that will make those top layers want to cave into the ditch. Adjacent (and not so adjacent) structures can be affected. I'd have to say that this situation was the most dangerous place to dig that I have ever seen.
Our solution was expensive, but may be necessary in your case: pre-drill soldier piles (H-piles) about 5-10 feet deeper than your trench goes into that hard rock, then drop in lagging (either trench plates, or wood) to brace the walls of the excavation. You probably will need an excavator-mounted hoe-ram to break the rock.
Good luck!
PS I make my living as an estimator, and I am not green enough to offer an off-the-top-of-my-head price on this one.
RE: Cost of trench Rock Excavation
If you are using a hoe ram, you must employ a "shelf" technique to be able to successfully get down to the required subgrade. Consider a hammer on a 100,000 excavator is approximately 24" wide (from center of tip of bit to outside edge of hammer housing). In order to get 20' down stepping in 1' at a time, the trench would need to be 40' at the top, stairstepping down and in.
My point is this - rock is expensive to remove no matter which way it is removed. It is extremely risky for all the parties involved especially contractors. To accomodate the overexcavation required at this depth or the cost of a massive trencher, do yourself a favor and figure a removal budget about 2-4x's what it theoretically costs to remove a CY! Good Luck!