# Fracturing Large Rocks



## roughster (Dec 18, 2017)

Hey Guys! Sorry haven't posted in this forum in a long time. I got tired of posting everything twice here and in NorCal. Anyways! I am currently facing a challenge that I am sure some of you have come across so figured I'd tap the collective power of the internet!

In the pic below, the rock in the blue circle is the offender in question. Obviously ruining the nice smooth berm flow we are going for  Here's the rub. That is the literal tip of the iceberg. That rock is a like the capstone of one of the Pyramids of Giza.










The other issue is this is as dense and solid columnar basalt as possible. Normally, this is not a bad thing, as attacking the "joints" usually yields immediate fractures and attack points. However, as fate would have it, there really aren't any joints in this section of rock we need to "chip" off AND the banding orientation of the rock is horizontal aka a vertical hit is perfectly perpendicular to the existing joints of which the first one is about 3 feet down and probably 500 lbs of rock between what you see and it. I also have no other options but to do this by hand, no heavy machinery is allowed here.

I have done some preliminary hard swings with a 7 lbs pick axe to ear shattering clanging and potentially tragic deflection with no progress. This is where you guys come in!

My general plan is to bring my cordless hammer battery 36V driver up there and drill in multiple holes around where I am "hoping" to fracture it, then using a chisel and sledge to just got to town. I don't have a breaker bar but if someone has a technique they think will work from a vertical attack point, I'll buy one.

I'm all ears to any suggestion! Thanks in advance for the wisdom I know is coming


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## 127.0.0.1 (Nov 19, 2013)

time
striking hammer
carbide tracer
wedges shims

and did I say time....time


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## roughster (Dec 18, 2017)

127.0.0.1 said:


> time
> striking hammer
> carbide tracer
> wedges shims
> ...


That's what I was hoping to not hear, but rather a magic solution!  I bought a wedge/feather set so will be going that approach unless that magical solution ... magically appears hehe


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## leaguerider (Sep 6, 2010)

Have you looked at Rock Splitting Mortar?
pour it in the holes you drill 

RockFrac seems to be one brand.

Home Despot has "Expansive Demolition Grout for Concrete Rock Breaking and Removal" $100 for 44 lbs


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## 127.0.0.1 (Nov 19, 2013)

you can use a bike trailer and lug a 2500 watt generator and makita or bosch electric breaker in 70lb range or higher, that will make the job faster at expense of more effort draggin out the tools.

https://www.boschtools.com/us/en/boschtools-ocs/breaker-hammers-bh2760vc-34552-p/

even with this it will take some time, but less


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## roughster (Dec 18, 2017)

leaguerider said:


> Have you looked at Rock Splitting Mortar?
> pour it in the holes you drill
> 
> RockFrac seems to be one brand.
> ...


Cool haven't seen that before. Have to give this some consideration! I like the idea of drilling some holes, filling in the stuff then letting sit and do the work for me! Trying to minimize the physical / force based-demo models if at all possible.


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## Fajita Dave (Mar 22, 2012)

I've never had to do that before but I imagine drilling a 2ft deep hole and dropping in some TNT would be fun!


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## roughster (Dec 18, 2017)

Fajita Dave said:


> I've never had to do that before but I imagine drilling a 2ft deep hole and dropping in some TNT would be fun!


Does TNT fall under a general expectation of "no heavy machinery"? lol


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## Fajita Dave (Mar 22, 2012)

roughster said:


> Does TNT fall under a general expectation of "no heavy machinery"? lol


Well it's definitely not machinery!


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## JustMtnB44 (Nov 8, 2004)

I just split a piece of rock yesterday with a cordless rotary hammer and set of feathers and wedges. I'm pretty sure the rock was sandstone and also not partially buried in the ground so definitely easier to work with than what the OP is asking about. It only took about 10 minutes to do this. It's hard to get a sense of scale here but the part I split off weighs at least 120 lbs, too much for one person to lift.


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## roughster (Dec 18, 2017)

JustMtnB44 said:


> I just split a piece of rock yesterday with a cordless rotary hammer and set of feathers and wedges. I'm pretty sure the rock was sandstone and also not partially buried in the ground so definitely easier to work with than what the OP is asking about. It only took about 10 minutes to do this. It's hard to get a sense of scale here but the part I split off weighs at least 120 lbs, too much for one person to lift.
> 
> View attachment 1341787
> 
> ...


NICE! What size drill bit did you use for that? Looks beefy!


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## Torgy (Mar 8, 2016)

Would digging out below the surface and using a cordless grinder with a diamond blade be something you could do? Then use some of the wedges to pound into the cut. Just throwing out an idea.


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## TylerVernon (Nov 10, 2019)

I'm pretty much the expert at cracking rock, and the good news for you is that all you need is a 16 lb sledge hammer and give it a couple of swings. You don't need any fancy gear, or big jack hammers, or special technique. You need maximum impulse on target. And unless you're bringing in a skid loader attached hydraulic hammer, a strong man with a sledge is the best way to get that.


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## Cotharyus (Jun 21, 2012)

The hammer drill and a set of wedges and feathers is all you need. It’s a 45 minute job, tops. Dig out around it some and lay into it. The wedges and feathers will dictate what size drill bit you need to use. I bought a Bosch Bulldog hammer drill years ago for just this purpose.


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## roughster (Dec 18, 2017)

Okay guys, the wedge and feathers arrive in the next few days hopefully. I'll try to get some pictures and post for those interested! If that doesn't do it, I have some of that expanding mortar on the way as well.


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## JustMtnB44 (Nov 8, 2004)

roughster said:


> NICE! What size drill bit did you use for that? Looks beefy!


For this set of feathers and wedges a 1/2" drill bit is needed. I drilled full depth of the bit, about 4-5", but could have gotten away with less.


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## TylerVernon (Nov 10, 2019)

JustMtnB44 said:


> I just split a piece of rock yesterday with a cordless rotary hammer and set of feathers and wedges. I'm pretty sure the rock was sandstone and also not partially buried in the ground so definitely easier to work with than what the OP is asking about. It only took about 10 minutes to do this. It's hard to get a sense of scale here but the part I split off weighs at least 120 lbs, too much for one person to lift.


I think you made that harder than it needed to be. Couple swings of a sledge and you would have cracked that rock in under 60 seconds.


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## JustMtnB44 (Nov 8, 2004)

TylerVernon said:


> I think you made that harder than it needed to be. Couple swings of a sledge and you would have cracked that rock in under 60 seconds.


Maybe, I've honestly never tried using a sledge for this, but I kinda doubt it since the vertical dimension at the split is about 15 inches. To me it's easier and less weight to carry the tools required for this method in a backpack than it is to carry a 10 lb sledge, all while also carrying other trail tools.


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## roughster (Dec 18, 2017)

Well since the wedges don't get in till tomorrow, and I was up there anyways, figured I try just WAILING on it with the biggest pick I have. Surprise surprise, I got most of it.









There are two sections that are just 100% pure compact basalt with no apparent weakness that despite full arc wind ups and bone shattering force just wouldn't break. If I bring the drill up and just drill in a few holes, I am sure I can probably get the rest without the wedges, but I'll save them for next time. Swinging a pick axe that hard is really sketchy. I had a few deflections that could've cost me a limb if I wasn't a ninja.


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## TylerVernon (Nov 10, 2019)

JustMtnB44 said:


> Maybe, I've honestly never tried using a sledge for this, but I kinda doubt it since the vertical dimension at the split is about 15 inches. To me it's easier and less weight to carry the tools required for this method in a backpack than it is to carry a 10 lb sledge, all while also carrying other trail tools.


I've spit many, many rocks larger than that with my sledge. When I was 20 my parents bought a house in a boulder field and wanted to improve the landscaping later. I started with a pick and bars, went to a jack hammer, then a bigger jack, then a sledge, then a 100hp skid loader. Went through a few subcontractors who just didn't want to do it anymore, lost a few friends too. 6 months later we hauled it all away - 18 18-wheeler loads worth of rocks. Yard looks great now. I'll f-up a rock. Impulse on target, only thing that matters.


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## Cotharyus (Jun 21, 2012)

TylerVernon said:


> Impulse on target, only thing that matters.


True, but there's a reason tools like wedges and feathers exist. If you swing tools as hard as you need to to bust this stuff up all day, day after day, it's hard on your body, especially past middle age. The right tools net the same results with little additional time necessary, and a lot less wear on the body. It's the "smarter not harder" thing.


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## OzarkFathom (Jul 2, 2019)

Right tool for the job.
Y'all are doing it wrong......

Ozark Gravel Sticks and a lighter, fit in your pocket....
View attachment 1343449


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## Harryman (Jun 14, 2011)

Boo for flow trails! Yay for rocks! That was a lost opportunity right there! 😁

I would have used that for something funky, but it’s your party.


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## Walt Dizzy (Aug 18, 2003)

*Feather and wedge*

This is the third and final split I made in a ~2'x2'x3' rock that was, much like the OP's example, right in the middle of an otherwise nice insloped turn.

The first split halved the rock evenly, but the halves were still too big for me to move. The overlying half didn't split cleanly a second time, but the chunk that came off removed enough weight for me to flip the remainder out of the hole.

The second half, shown in the picture here, split pretty evenly. I had little difficulty rolling the pieces out of the way.

I don't know what tools the OP has available, but a ~4ft steel bar is my essential tool for prying rocks up out of the ground.

I use the largest Makita rotary hammer that will run from a small Honda generator. I was able to move everything to my worksite in a single wheelbarrow load, just barely.

Having multiple drill bits is most helpful because they will fail from the heat generated from drilling unless they are changed frequently and allowed to cool.

Hard rock, such as granite, actually splits better than softer rock. But drilling into hard rock is not easy.


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## OzarkFathom (Jul 2, 2019)

Lotsa Sisyphuses around here.....


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## PierreR (May 17, 2012)

I've got some experience in breaking up hard rock. The big hammer idea is a good one. You need the right size boy a six pack and the right size hammer. I have seen the time when you could hit a rock all day with a 10 lb sledge and get nothing but use a 18 lb hammer and a few swings does it. 
Nothing harder to bust than spinels. I had a 30 lb sledge and a boy of 7'1" tall and 485 lbs. No problem swinging a few licks and breaking off pieces. You could sit there with a 90 lb jack hammer and just mushroom chisels on that stuff. It takes high energy shock to break rock. The big hammer idea works best with hard rocks and not as much with soft rocks. 

1 1/4" rock drills and number 4 ditching works great too but disturbs wildlife and bureaucrats.


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## mbmtb (Nov 28, 2013)

Isn't this exactly what a Sierra Blaster is for?

Never used one but know others who have... surprisingly only a few posts on this forum about them?


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## 127.0.0.1 (Nov 19, 2013)

^round my parts the last thing anyone wants to do is bust rock. we purposely include as much chunk as possible...


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## Fleas (Jan 19, 2006)

Torgy said:


> Would digging out below the surface and using a cordless grinder with a diamond blade be something you could do? Then use some of the wedges to pound into the cut. Just throwing out an idea.


When we've had to just nip the end off of an exposed rock, rock face, or edge, our "rock guy" (he has the grinder) would put a series of closely-spaced slots into the rock to the correct depth, then just chip off the pieces. In most of our cases, the resulting surface is a rideable surface with super traction, and the desired contour. I would think the same technique would work here - only that the resulting surface would ultimately be buried.

I think this was also used to fit rocks together, or create a notch for setting a wood feature. The slots result in a much more predictable fracture or notch.

-F


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## Walt Dizzy (Aug 18, 2003)

127.0.0.1 said:


> ^round my parts the last thing anyone wants to do is bust rock. we purposely include as much chunk as possible...


Got that covered. We have more f-ing rocks than anywhere within a hundred miles. We have rock gardens that make people cry, and bike store owners dance for joy. I like that stuff, but I also like to let off the brakes and let 'er rip on the downhills. It's not an either-or choice, we've got both.


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## Moe Ped (Aug 24, 2009)

Splitting rock is an unusually satisfying task, seems like it should be more difficult than it is.

This video is of our volunteer team removing a multi-ton boulder (a small bulldozer couldn't budge it) that was blocking a park road.






For reasons I don't totally understand it works best to split a rock in half and then halve it again and again. Trying to take a small piece off of a large rock never works well unless there's obvious cleavage planes.

Another thing we learned on this project as we went along is that wet drilling easily doubles the life of the drill bits, makes drilling faster and keeps down the drilling dust.

For the OP example I think I would have left it there and built up the berm with more rock (think pavers/cobblestones); this would make for a rather unique corner that would last "forever".


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## tbmaddux (May 22, 2012)

That rock was a beast!

When he started I was thinking “I wonder what happens if he bottoms out all those pins flush with the rock surface?” and the video pleased me with an answer!


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## Walt Dizzy (Aug 18, 2003)

Moe Ped;1483806This video is of our volunteer team removing a multi-ton boulder (a small bulldozer couldn't budge it) that was blocking a park road.
For reasons I don't totally understand it works best to split a rock in half and then halve it again and again. Trying to take a small piece off of a large rock never works well unless there's obvious cleavage planes.
Another thing we learned on this Splitting rock is an unusually satisfying task said:


> My guess about the superior outcome of splitting rocks in half vs taking a smaller piece is that the crack will always take a shorter path if available. With anything less than half, that is usually out the side.
> 
> Using water as coolent/lube does extend the life of the bit, however, the drilling dust can form a natural cement and lock the bit into the hole. Having 3 or more bits and switching frequently between them prevents bits from overheating or getting locked into the bore hole.
> 
> ...


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## TwoWheelMan (Jan 5, 2009)

For the rock in the OP's post, I think I'd try a sledge (or leave it - depends on the trail).

I often split granite and ironstone for fabricating building stones for tread, walls, and bridge footings, or to simply move a giant boulder out of the way. We also hand-smash granite with sledges to make aggregate. In general, we have lots of rock and not a lot of dirt...

Wedges and feathers work great. It's not difficult to start (though you do get better with experience) and is very satisfying. This is some of what I've learned:

- avoid undersized wedges. My rule of thumb is a rock depth no more than 5X the wedge depth. My most used wedges are 3/4" diameter, which requires a 7/8" hole. Drilling large holes takes longer, but that is still better than the inefficiency of not having the rock split at all!

- a good rotary hammer makes all the difference, if you are going to do much splitting. I'm currently using a 36V cordless Hilti SDS-Max, and it is a dream.... A corded tool and 100lb generator would no doubt be better but is not usually an option where I am working. I have tried a few high-end SDS-plus tools, and they work fine in concrete and sedimentary rocks like sandstone, but are too slow in granite.

- Never lean hard on a rotary hammer, or you will kill an expensive bit very quickly. Only use enough pressure to keep the bit hammering. I think most people familiar with tools already know this, but it can be an expensive and common problem if new crew or volunteers are involved. For this reason, and because splitting requires some intuitition that develops with experience, I tend to do all the splitting myself. Besides, it is fun 

- bits vary. The consumer-brand bits I get from Home Depot give half or less of the service life of a good industrial bit (like Hilti) and the prices are similar.

- for small rocks, you need to split in half. For really big rocks, you can get away with non-symmetric splits but not -usually- if the edge is nearer than the depth. The crack 'wants' to go to the nearest free surface once it has propagated much beyond the wedge depth. Using more wedges and drilling deeper holes sometimes can be used to circumvent this behavior.

- following from the above: drill your holes ~perpendicular to the surface. If you don't, you may find the rock 'unpeeling' instead of splitting.

- plan and complete your splitting in advance of when you need the finished materials, especially if you are using a cordless drill (which gives a finite number of holes/day). For some projects, I've split rocks for an hour/day (a couple of batteries) for a week, so all the material is on hand when the rest of the crew starts the build. Drilling granite is also noisy, dusty work -- no fun for others to be around.

I've used expansive morter too. Given a choice I'd use wedges and feathers every time instead, even if it is just to bust the rock into something movable.

Bearing surface on bridge abutment:
















A rock 'bridge' made of split slabs, bridging a gap between two bedrock outcrops. Each slab is about 3ft wide








Building a transition at the bottom of a granite roll-down. This started as one 2m x 1m granite boulder, which was split and partially smashed to form the transition.








splitting process








bridge footings (we needed two, and this boulder intact was too awkward to winch/rock bar anyway)

















Example of tread being built mostly with split granite building stones. In this case a curved ramp climbing up to a bedrock slab (eventually topped with dirt).


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## roughster (Dec 18, 2017)

Dude awesome post thank you!


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## Walt Dizzy (Aug 18, 2003)

Wow, thanks for a great post!


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