Big rock---I give up----I'll just move my new house instead

[gordon21]

I have been excavating into the side of the mountaintop in my part time for the last several months for the house I am building. My little JD 790 was doing a great job excavating the first 100 or so cubic yards of material. Mostly 6"-12" of topsoil, stumps, rocks the size of a 35" TV and smaller. I had to clear a flat level spot about 55' long into the side of the hill to accomodate the house footprint. All went well for the first 45' or so. Then I hit solid rock. If you look close, you will see that it was hidden just under 12" of topsoil. No one around here knows what type of rock it is, but it is the hardest stuff to break up.

We broke a huge rental skidsteer one weekend. Then we got it back the following weekend and broke the 2.5" thick bit on the hydraulic breaker!!! Then we hired a 12,000# excavator with another hydraulic bit. He worked 2.5 days and finally gave up. He charged me essentially for mileage and diesel only. We then tried to take it out by hand with a 90# electic jackhammer. That worked for 4 weekends until we broke the jackhammer. I then threw in the towel and decided to move the house 5' to one side and 5' farther out from the hill. That necessitated using step down footers and another set of delays.

The rock is bright white, extremely fine grained, has few seams and when you do find a seam, it will curve erratically. It tends to powder, not split when pounded hard even with a pointy hydraulic bit. Granite is common around here and this stuff is several times harder to work than granite.

The attached pix show what a 790 will do in removing the side of a mountain. The walls in the pix are only half done. You can see the massive rock we encountered on the back wall of the house. The rear footers had to be dug down into solid rock. The rear wall had to be 12" thick because it will have over 7' of fill up against it when done. The top of the 10' basement walls will stick up about 2' higher than the top of the rock. The rock wall is about 9' high from the bottom of the footers to the top of the rock.

 

[wushaw]

I bet a hammer drill and TNT would have worked.

Looks cool though

 

[gordon21]

My new 208' deep well was already installed about 30' from the house. I did not dare to blast. I put the well in about halfway through the excavation. Building a house before the well is a HUGE risk.

The HGTV home they built a couple years ago and featured on TV in Lake Lure was a multi million $ home built as the first residence in what was to be a very exclusive community on the top of a large solid rock mountain. Did I mention solid rock??? They drilled a 1200' well AFTER building the TV home. No water. They then drilled over 100 WELLS many of which were 1000' or deeper. Not a drop of water in any of them. At one point, they had a dozen different well drillers working at one time at various places in the development.

Needless to say, the owners of those lots were upset. Some of the lots being sold were for upwards of a million dollars just for the lot. The winner of the HGTV home sold it back to the developer. You can't get a certificate of occupancy without water. You can't move in without the CO.

Never build a house without your plan for water in place.

 

[swampvol]

I have a few acres just west of you in Brevard.
Hopefully will be building in a few years, and hopefully don't encounter that rock.

Wushaw has a point..drill a few holes and pack it with tnt.



oops..you must have made that post while I was typing.

 

[Slacker]

That looks alot like what I call sandrock. It's a pain in the butt. I sunk 24x36 footers into it for my hunting cabin. I dug two footers in a week then hired a 3 man crew for the others. Try this method:
Buy a bucket of rapid expanding cement. It's used to secure bolts into concrete. When its mixed with water it gets HOT. Drill a hole and fill it. The expanding action may crack the rock for you. I'd give it a shot if the alternative was moving a house. Small rock blasting isn't a risk to your well if done correctly.

 

[Z-Michigan]

Similar suggestion: look up "Dexpan non-explosive demolition agent." Basically super-expanding cement. Only works if you can drill holes in the rock though.

 

[gordon21]

I tried Dexpan. All it did was break off little pieces. Dexpan works best if the rock has seams or a grain or will split along a string of Dexpan filled holes. It didn't work. This rock is so hard it powders before it will split.

On other rock that can be drilled, Dexpan works great.

 

[Z-Michigan]

Sounds like you've tried a lot of things. Out of curiousity - if the rock powders, did the 12,000 lb excavator try just digging through it with a small bucket?

 

[zzvyb6]

Too bad house is now so close. I've dealt with similar rock problem using charcoal, railroad ties, and diesel fuel. Build a moat and a fire blanket to keep the heat in. Fire it up all around the rock to be removed. Add some air if you have a fan to add a blast furnace effect. Let it burn all night. You'll soon hear some cracking, then toss on 55 gallons of cold water. Usually wind up with baseball size pieces. Reduced in size to a manageable pile. Now bring in the backhoe.

 

[jt7157]

This is the first time I've tried to post an image, but I don't know if I'm doing it correctly. If I am, see the picture of a hydraulic rock splitter attached to a trackhoe. The whole thing weighs 100,000 pounds, and it split limestone as if it were ripe watermelon. I don't know if it would work on the hard rock you've been fighting, but I thought I'd show how I had some rock taken care of in case others might need to do the same thing.