I am designing a product that needs to be installed in a trench that is ideally at least 15' deep and approximately 20' long. The trench does not need to have vertical end walls. I would prefer a narrow trench, but it can be whatever width fits the excavator's needs. I would like the excavator to be able to access the rear yard of a typical suburban yard. Which excavator would you recommend that could do the job efficiently but have a small footprint both to minimize transportation costs and to permit access to the greatest number of job sites? Thanks for your professional guidance!
15' deep is a big machine, it is also an immense pile of spoils. a 10~12 ton machine can dig 15' deep, barely. Shoring is another big question. Trenches like that don't stay open in all conditions. If you are thinking you can make this thing and get it into a city lot backyard without tearing up the whole place, you need to re-think it from the standpoint of what the trench really looks like, the spoils pile, the shoring, setbacks.
I appreciate your cautions. I am targeting suburban/rural, not urban. Two-thirds of the spoils would be hauled away as created because the item inserted would be grouted in place with only the top third of the trench refilled with spoils. My assumption was that shoring would not be necessary as the trench would be filled quickly after it is dug but correct me if I am wrong. Would something like the Cat 308 CR be able to do the job?
Just curious did you read my post at all? I said 10~12 ton unit and barely at that. There is no sneaking in anywhere and digging a 15' deep trench. 15' deep does not just dig like a slot in wood every time. If it is gravelly soils, picture this: for every foot down, add 6" to the width of the trench at a minimum. So if you are digging with a 2' bucket, then the top of the trench will be about 10' wide, give or take. And it will be falling in the whole time you are digging it and will continue to seek equilibrium. That is also going away from you, so now a 12 ton machine may not be able to keep the trench open as it backs up. Do the triangle thing on that trench. 10' wide at the top = 5.5 foot average width. The spoils piles are tremendous.
That is amazing. I am used to the clay soils of my area. I never imagined you would need to create such a wide triangulation to reach a 15' depth. I agree that would not work.
We can and have reached 8 ft down here with a 12in wide bucket with no taper. It's doable in clay sometimes. As skyking mentioned, that's gonna take a large machine. Just that means your looking at a wider trench so the boom fits in it. A Cat308 is an 8 ton machine. Gonna need a Cat 312 or larger to effectively dig that deep.
OP what are you installing? Does anyone have to get into this excavation to fine grade the bottom before setting what you are installing? If anyone is getting in a 15' deep excavation it needs to be shored, shielded or properly benched.
There is a way to maybe do the job with the machine listed above. To do the job, lay out the 20' long trench. Then start about 12' away from the start of the trench and dig a ramp 8' wide by 12' long going down 3-4' deep about 2-3 foot into the start of the trench depending on if the stick is long or short for the reach to the end of the trench. This drops the whole excavator down 4' or so, making the depth to dig not as bad. You will need to excavate out for this process an extra 12 yds or so of dirt just to make the access ramp. Amount of additional dirt for the trench based on 30" wide or so is up to 36 yards or so, or 3 qty full size dump truck loads. As everyone has said, you can't go into the trench unless you install aluminum shoring. The amount of dirt/spoils this would take up might be the entire backyard of a subdivision house, and the machine, and dirt would likely ruin the lawn unless for every bucket of dirt you excavate, it goes right into either the dump truck or a loader machine bucket and hauled off.
No one needs to enter the trench.
How wide a trench?
Exactly^^^ We do a lot of deep trenching for testing purposes, not uncommon for a 15’-18’ deep trench dug with a 21 ton machine to be 10-15’ wide at surface. A tremendous amount of spoils is the result... Loose or semi consolidated gravels: side wall ’spalling’, undermining…quickly end up with a huge unstable excavation. Clay: not uncommon to be subject to hydraulic pressure, damp swelling clays can result in large sections of sidewall suddenly releasing…
Thanks everyone for your insights. You have made clear that deep trenching is far more challenging than I had realized. I am going to go back to my design and see if I can figure out a way to avoid it. Thanks again!