excavating basement foundation, and rotating laser technique
I am getting set to have my basement foundation excavated (new home) and will likely have to guide the excavator myself using a rotating laser level.
I’ve done total station surveying, digital level loops, grade stakes, sewer layout stakes etc before but would appreciate some input on how best to do the (residential) task at hand.
One possible option would be to set the rod a foot short (excavation too shallow) and when that elevation was met, tell the excavator to go another foot deeper. What I am trying to avoid is blindly digging and then checking, only to discover its too deep. (My geotech will require compacted granular fill to make up over-excavation.)
Is this a reasonable approach?
I’d really like to hear your techniques and experiences.
A good digger can maintain damn close to level with a hoe. You get one spot right on carefully, giving them "Down" ---"2 inches" and they'll peel it down right on and go from there.
Is this operator new to this?
Remember, a bit too deep only requires a bit more footer thickness-you shouldn't have to add stone and compact.
Is this operator new to this?
No but I am.
I have lots of experience in heavy civil work and survey (for example we had a 200 ton crane on site today) but this crew-of-two and the finer points specific to basement excavation are new to me. My geotech is anal and will require compacted granular fill to make up over-excavation. Could even require proctor testing, who knows.
The key for me is to have good info and avoid over-excavation while using the excavator efficiently.
What does your geotech consider "over-excavation"? A quarter inch? An inch? Three inches? A foot?
Most guys who do this for a living simply set the laser at exactly what you need....if you're shallow the laser detector pole is leaned to the side to get a signal - guys who dig for a living understand this and you probably don't have to say anything other than show him from time to time. If you're really anal and on a tight budget try to have your footers slightly shallow (1" to 2" max) and finish the final grade with a shovel - this gets old very quick.
On the other hand if you are anal and have a little more money and not so much time make sure the footers are at least as deep as needed...the slight over digging is simply made up with deeper footers - relatively cheap if your time is worth anything.
When working around any equipment, make sure the operator sees you before you get into range of the bucket.
hand digging glacial till not really an option
Buddy of mine tried that on his house and ended up "digging" with a small jack hammer. Admitedly his till was very hard.
Thanks for the "tip" about leaning the detector rod. That makes perfect sense and is a lot less fussy than constantly adjusting the detector up and down to figure out where you are.
The visibility tip is also very good. Some of these guys get the bucket swinging around at 20 or 30 mph! I've got full PPE and a visi-vest is highly recommended. Some pre-work discussion about what is going to take place and where I will stand etc is also highly recommended.
excavating with laser
It really depends on how good the operator is.
We have used almost exclusively DC10 Caterpillars. 6' wide bucket with 2" rip teeth made the excavation nearly pooltable level.
Works also very fast