Was talking to someone a while back and they said "it's close enough". My questions are: 1. When you are digging a basement or crawlspace what do you keep your tolerance depth, width and length wise? +/- 1/2" of target? 2. When grading with a skid steer how flat do you keep your tolerance? If there are dips in dry hard clay do you keep them within +/- 1/2"? Where I am there is no top soil at all its just all clay. I find it very hard to get a smooth grade because you can't just "skim" a little bit off because it rips out chunks or "pizza's" of clay an inch thick. Also using a Cat 279D where the whole undercarriage and track pivots (not to be confused with the multiple roller suspension undercarriage type). I find that the rocking motion you get from the torsion piece makes it hard to grade as well. As soon as it bites the machine rolls forward or back separate from the tracks and makes it hard to cut a level grade. Just curious if anyone else has experienced this? Thanks!
Cant speak to solid clay but for footings I dig to bottom of tone on the laser and call it a win if doing pad work I stipulated plus minus a 10th of a foot tolerance Doing finish grading for concrete I am looking for a quarter inch but that's specialized work
+/- .10th' is common spec and expectation here as well for most commercial jobs we do. If the pad has to be dead on we'll use our laser box blade on a 279D to get it darn near level. We have 2 279D's and I think they are great finish grading machines. Now both have the rear factor counterweights that really make a difference. In my experience there is only 2 ways to grade a heavy, sticky clay. Either overfill the area and carefully shave it to grade or cut it out a couple of inches from finish grade, break the clay up and spread to grade. If you have the luxury of importing suitable grading fill then leave the finish grade a few inches low and cover. Just finished up a Starbucks where the entire site was awful fat, heavy clay. We backfilled behind curb with onsite material (heavy clay spoils) and held the grade down 2-3" for topsoil. First landscaper walked away because he couldn't do anything with the sub-grade. Second landscaper comes in, top dresses everything with screen topsoil and rocked on.
Final grade makes a difference. Normally final/finish grade wants about 4" of topsoil. If you're below that with rough grade you can usually just add the topsoil as long as you're reasonably close and have proper drainage. If the ground is really uneven and hard packed clay, you need to break up the material so it can be leveled. Sometimes adding water makes it easier to work with. I think that's why a lot of work alongside of hwy's. and such is done with excavators using clean up buckets. Graders can also shave material easier than a skid steer or CTL. Worst case is you over dig the material so you can break it up. Then you can more easily spread it as required. I'd sometimes just turn sharp and swing my tooth bucket side to side to shave small mounds off. The sides of the teeth worked pretty good and gives you a little bit of fine material for filling low spots. The teeth on my bucket are bottom mount but the flush mount should also work.
You guys rock! This is exactly what I was looking for! I started this because I've got "chiefs" on both sides of the fence of what is "good" and I started a business a couple months ago with a skid steer and mini excavator so I am defiantly green. My father is a residential new construction contractor of 25 years or so and I just dug a crawlspace for him (which I didn't design my business for as I don't have a large excavator). I was probably within 2" in hard clay using a standard laser transit on a stick getting out and checking every so often. I'd really like to get a arm mounted receiver but one step at a time. He wanted to see the entire hole within 1/4" so he wasn't the happiest camper but he knew what to expect before we started. We dug majority of the hole with the mini and pushed away the material into a pile with the skid steer. He says I should have dug it entirely with the skid steer and left the mini at home and it would have been faster to project completion. (Due to build we made a ramp which the skid steer could get down inside.) I just don't see how this would be possible when the skid steer ran non stop trying to keep the excavator piles moved.
Loaders are a very efficient way to mass ex a skid steer is just a loader and if your hitting trucks with your dirt skid steer is definitely loading faster than a mini That said I have done jobs similar to that with one backhoe or 2 backhoes working together or an excavator and backhoe to move the dirt or with a loader I have also done them with minis and a skid but keep this in mind run what you have rentals wat the bottom line especially when you park a machine with payments to run a rental and learn how to make your machines do anything you want anything will leave a perfect surface if the operator is good enough
I've dealt with numerous customers/gc on jobs who baulk at the mini ex and say "why didn't you bring a skidsteer it's way faster" it's because they don't know what they are talking about. My 6 ton mini will out dig my 75hp CTL like nothing. The CTL is only faster if the mini ex is moving dirt 2 or 3 times. It's closer if it's moving loose dirt, but virgin dirt the mini is way faster. Here it's generally +-1" on a dig, excluding really minor areas that might vary a bit more. There is a reason why footings are formed with 2x6, because they only technically need to be 5.5" minimum and to allow for variation in the digging. Problem is so many have gotten lazy, if there is 20 minutes on a shovel on a 2000 sq/ft basement to make it nearly perfect cribbers here will complain.
On the speed subject (especially in loose vs undisturbed soil) that was my take but I don't want to be the new guy who acts like I know everything because I'm a long way from that. Just trying to get a feel if I do more crawlspaces what I should bring in. I suspect my accuracy will improve in time too as I just dug my first crawlspace with under 12 hours experience operating mini's and CTL's in my entire life. Thank you guys for your replies this is really helping me out tons!!!
Around here we almost always have to bring in some sort of crushed/screened material to get a decent tolerance. Otherwise it's based on the average size of the rocks in the native soil (usually 6-24"). Rarely is the native material good enough to get a decent finish grade with.
I'm in the undercut and use a workable material to top up to grade school of thought Not a lot of clay around here, but if it is there, it must be undercut 2 feet, covered with a geotextile cloth, and the back filled with a clean sandstone to within 4 inches of grade, then brought up the last 4 inches with sand. We get a lot of frost here, so anything over 900 square feet has to have a footing, and an 8 foot frost wall, or an engineered pad with a 2 foot thickening. If it is an attached garage, it has to have the 8 foot walls. One thing about under cutting, there comes a point that buying a bit of fine material to top up, is cheaper than the time taken trying to fine grade difficult material.
Very good point on the last statement "One thing about under cutting, there comes a point that buying a bit of fine material to top up, is cheaper than the time taken trying to fine grade difficult material." I appreciate your response! Thank you!
If I had to choose a 279D CTL or a mini-ex (12,000 lb or less) to dig a crawlspace I would pick the 279D every time FWIW.
Today's job illustrates my point
Oh wow yeah that would make it challenging!