A question of caissons

[mstovall]

First off, sorry for the long post. That said.........

I have a project overlooking the lake coming up and I am currently working out the budget. The house is going to be on 8x8 posts (44 of them) , with CB88's on 16" diameter sonotubes with the caissons (same dia.) extending 2' into solid rock with a 3' deep probe hole to insure no voids. The site has between 2' and 4' of Colluvium over weathered limestone. Geologic survey for the area shows the weathered limestone may only be 1 foot thick with a colluvium layer before hitting solid rock (probably the reason that a $2 million house close by has moved 1').

I am having a tough time finding anyone local who has a rig that can or wants to operate on the slope (20%). There are few here that have a track drill and those that I've talked to really don't want to do it (the site is 6 miles back on a fairly narrow ridge road).

Okay...now the question (bet you wondered if I'd ever get to it). Has anyone here ever used rock drills and jack hammers to drill caisson holes on tough access sites? I can get a backhoe down the slope without too much trouble, so I can dig a series of trenches to expose the rock. I do know that there will be the danger of busting off the "edge" of your bore which may then necessitate epoxying dowels.

Any Ideas (I'm trying to keep the budget somewhat reasonable).

Thanks
Michael

[mstovall]

Re: A question of caissons

Well....... no comments, but I'll pass along the latest for those interested.

I found a track driller who can punch a series of 4" hole around each 16" hole. I'll jack hammer out the center. I am also going to increase the diameter of the probe hole (drop a #6 dowel and vibrate it in) and have the driller punch that one too. He can have one caisson hole complete in about 10 minutes. He'll be on the hill between 16-20 hours, so this will be a cost effective solution. If anyone is interested I'll take photos of the project.

Michael

[BigLou80]

Re: A question of caissons

Mike,
sounds like a neat project. I would be interested in seeing some pictures


Lou

[Lavrans]

Re: A question of caissons

Any Ideas (I'm trying to keep the budget somewhat reasonable).

Michael- Sorry, no advice to give- only a comment: is it possible to have a reasonable budget for a foundation like that :-)

I'd love to see pictures too.

[mstovall]

Re: A question of caissons

Lavrans,
I had one sub look at it, wanted the slope terraced before he started, and wanted $100,000 for 44 holes (i.e. he did not want the job).

I think I have found a $8000 solution.

Michael

[Thor]

Re: A question of caissons

No alternatives but here is what I experienced on a much smaller scale and not near a lake.
Caissons were to be drilled to "refusal". That could be the limestone (my guy did not use a truck mounted rig) depending on the downward pressure when drilling.
The guy I used had rebar cages about 20 feet long prewired. He also had concrete trucks lined up to be on site within an hour of drilling the last caisson. Told me he didn't want to take any chances of ground water seeping into the holes.
It was drilled, rebarred and poured within one work day.
The drilling rig was constructed by the sub I hired. He explained it was perfect in underground parking garages when the slab needed support so he would penetrate the concrete, move in his unit (fit on a tandem axle trailer), drill to refusal, rebar the hole and use a concrete pumper. I haven't seen anything of this guy for years (Denver area). He may have moved elsewhere. SUMMARY:
1) track or truck mount not the only way. 2) Prep for water filling hole 3) Prepare rebar cages (this guy was fast) 4)Pour concrete immediately. Thor

[mstovall]

Re: A question of caissons

Thanks Thor,

I have to go into the rock to make sockets. Probably won't hit ground water as the site is 120 ft above the lake elevation. My biggest problem is liable to be karst formations.

Michael

[always-learning]

Re: A question of caissons

Wow!

Sounds like one of those jobs that no one will touch with a 100' pole, never mind the 10 footer.

Kudos to you for getting involved. Hope to see pix of that one....


Any engineer friends? How about contacting the state licensing bureau for engineers, or maybe the Army Corp. I'm sure someone can help.


Good luck

[mstovall]

Re: A question of caissons

Hi Chuck,
Yeah I've tapped into all the Geotechs, Structural Engineers, and Civil guys that I know. I finally found the track drill guy through a track drill equipment dealer. It can be rough put together a reasonable budget when you have to deal with such specialized trades. I was fortunate. He's a driller and blaster. He wanted to blast them and I had to remind him that I need caisson holes and not craters!

Michael