We run a Cat 305e2 that we use for site work for custom homes. Recently we got a request to drill pier holes for some CMU retaining walls. This would be a new scope for us and am looking for any advice. The pier holes will be 18'' diameter by 12 feet deep. We have a Cat 19b auger motor that we have used to drill post holes. So I guess the main question is, will the 305 handle this job. Oh yeah the soil is a silt clay down to about 5 feet then weathered serpentine shale. and how do you get the holes cleaned out that far down. Any advice appreciated. Thanks
How many holes? It's gonna be a biotch. By clean out I assume you mean get all your spoils out of the hole as you go down? That's gonna be your biggest task next to the auger you use to drill that shale. It's surprisingly hard. Anytime we drill shale we're using an auger with carbide tipped bits. It's abrasive stuff and takes a fair amount of crowd pressure and drive torque to drill. Back to the clean out, keeping that style setup plumb all the way down 12' is gonna be tough. Beyond that task you're gonna have to be able to bring the auger up each time it's full and spin it off. At least with a little hoe you can just swing and spin backwards to clean off. The only feasible way I see is to make yourself a 12' continuous flight auger, assuming you can lift it high enough to get in the hole. That way most of your spoils come out to the surface. The other way would be to make an extension for the auger you get so you can achieve a depth of 12'. It will create a challenge to bring the tool out of the hole and spin off after each bite. Research and see if they give a spec for the torque your auger motor produces. That will tell you how effective it will be turning an 18" auger in shale. I can go on and on but a little more info will help me give better guidance.
Junkyard, The Cat 19b drive motor puts out 3040 ft. lbs. of torque. We have 14 holes to bore. I was planning to use the auger that the Cat dealer sells which is about 4 feet long then use extensions to get the length. The motor itself is about 3 feet long and will fit down the hole.
While not impossible with 3,040 torque....it's gonna take awhile. What does the auger have for teeth or bits on it? We have some shale around here that drills fairly easy and some that's more like rock. Biggest thing if you attempt them is to go easy the first several feet and make sure you start dead plumb side to side as well as fore and aft. Side to side will mean a level pad or blocking to level the machine. It's like anything else, start off a smidge and 12' down you're off a LOT. For your purpose that's probably not a huge deal. Tell an inspector a 72" 45' shaft for a bridge pier is off......not good. If/when you get the hole to depth, throw about a gallon of water down the hole and spin in out fast with the auger barely touching the bottom of the hole. That'll help clean it out nice. Are they setting rebar cages in them or some sort of structure? We generally don't get very far ahead of the rebar and concrete to prevent losing a hole. Something to think about. At 12' I doubt you'll see water unless you're near a creek or something so no worries there. I'll help ya figure it out anyway I can. If you can send some pics of the auger and the teeth/bits it's got that helps. The button or SMO style bits won't take as much torque to run in the shale as a dirt tooth would. Kind of the difference in a rock bar and a shovel in hard dry ground. We drilled some shallow shafts in a building with a skid steer mounted auger drive one time when we were in a jam. About 18" if memory serves. After a few holes we pretty well used that little sucker up. I don't know how it compares to yours. To be continued
Junkyard, Thanks for the valuable advice. I am looking at getting a 18'' carbide button type auger from either Pengo or Cat.
I was thinking today driving along. Drilling in the dirt isn't much different than steel. If you have to, drill your first hole smaller then you can step up until you get to 18". It'll make things easier on that hydraulic drive.
We’ve dug a lot of 18’’ holes 8’ deep with an auger drive on a 100hp farm tractor. The auger only has 2’ of flighting with another 4’ of shaft, so we end up with the drive down the hole as well to get to 8’. As you say Junkyard, the operation is much quicker if we run a 12’’ pilot down first. The 18’’ follows the pilot hole surprisingly true.
I recently dug a couple 18" holes 8' deep with a 4' auger and extension using my skid steer. It worked well but you have to be careful to keep the hole straight. A little tilt is a long way off at 8'. We stopped the auger every once in a while and put a level on it to check alignment. Be careful once you get the top of the auger flighting below surface. It is very easy to bend the top of the flighting when coming out of the hole with dirt on top of it. By that I mean once you have the extension in the ground only go a little bit at a time and then lit it out to clean it.